<!-- doc/src/sgml/monitoring.sgml -->

<chapter id="monitoring">
 <title>Monitoring Database Activity</title>

 <indexterm zone="monitoring">
  <primary>monitoring</primary>
  <secondary>database activity</secondary>
 </indexterm>

 <indexterm zone="monitoring">
  <primary>database activity</primary>
  <secondary>monitoring</secondary>
 </indexterm>

 <para>
  A database administrator frequently wonders, <quote>What is the system
  doing right now?</quote>
  This chapter discusses how to find that out.
 </para>

  <para>
   Several tools are available for monitoring database activity and
   analyzing performance.  Most of this chapter is devoted to describing
   <productname>PostgreSQL</productname>'s statistics collector,
   but one should not neglect regular Unix monitoring programs such as
   <command>ps</command>, <command>top</command>, <command>iostat</command>, and <command>vmstat</command>.
   Also, once one has identified a
   poorly-performing query, further investigation might be needed using
   <productname>PostgreSQL</productname>'s <link linkend="sql-explain"><command>EXPLAIN</command></link> command.
   <xref linkend="using-explain"/> discusses <command>EXPLAIN</command>
   and other methods for understanding the behavior of an individual
   query.
  </para>

 <sect1 id="monitoring-ps">
  <title>Standard Unix Tools</title>

  <indexterm zone="monitoring-ps">
   <primary>ps</primary>
   <secondary>to monitor activity</secondary>
  </indexterm>

  <para>
   On most Unix platforms, <productname>PostgreSQL</productname> modifies its
   command title as reported by <command>ps</command>, so that individual server
   processes can readily be identified.  A sample display is

<screen>
$ ps auxww | grep ^postgres
postgres  15551  0.0  0.1  57536  7132 pts/0    S    18:02   0:00 postgres -i
postgres  15554  0.0  0.0  57536  1184 ?        Ss   18:02   0:00 postgres: background writer
postgres  15555  0.0  0.0  57536   916 ?        Ss   18:02   0:00 postgres: checkpointer
postgres  15556  0.0  0.0  57536   916 ?        Ss   18:02   0:00 postgres: walwriter
postgres  15557  0.0  0.0  58504  2244 ?        Ss   18:02   0:00 postgres: autovacuum launcher
postgres  15558  0.0  0.0  17512  1068 ?        Ss   18:02   0:00 postgres: stats collector
postgres  15582  0.0  0.0  58772  3080 ?        Ss   18:04   0:00 postgres: joe runbug 127.0.0.1 idle
postgres  15606  0.0  0.0  58772  3052 ?        Ss   18:07   0:00 postgres: tgl regression [local] SELECT waiting
postgres  15610  0.0  0.0  58772  3056 ?        Ss   18:07   0:00 postgres: tgl regression [local] idle in transaction
</screen>

   (The appropriate invocation of <command>ps</command> varies across different
   platforms, as do the details of what is shown.  This example is from a
   recent Linux system.)  The first process listed here is the
   primary server process.  The command arguments
   shown for it are the same ones used when it was launched.  The next five
   processes are background worker processes automatically launched by the
   primary process.  (The <quote>stats collector</quote> process will not be present
   if you have set the system not to start the statistics collector; likewise
   the <quote>autovacuum launcher</quote> process can be disabled.)
   Each of the remaining
   processes is a server process handling one client connection.  Each such
   process sets its command line display in the form

<screen>
postgres: <replaceable>user</replaceable> <replaceable>database</replaceable> <replaceable>host</replaceable> <replaceable>activity</replaceable>
</screen>

  The user, database, and (client) host items remain the same for
  the life of the client connection, but the activity indicator changes.
  The activity can be <literal>idle</literal> (i.e., waiting for a client command),
  <literal>idle in transaction</literal> (waiting for client inside a <command>BEGIN</command> block),
  or a command type name such as <literal>SELECT</literal>.  Also,
  <literal>waiting</literal> is appended if the server process is presently waiting
  on a lock held by another session.  In the above example we can infer
  that process 15606 is waiting for process 15610 to complete its transaction
  and thereby release some lock.  (Process 15610 must be the blocker, because
  there is no other active session.  In more complicated cases it would be
  necessary to look into the
  <link linkend="view-pg-locks"><structname>pg_locks</structname></link>
  system view to determine who is blocking whom.)
  </para>

  <para>
   If <xref linkend="guc-cluster-name"/> has been configured the
   cluster name will also be shown in <command>ps</command> output:
<screen>
$ psql -c 'SHOW cluster_name'
 cluster_name
--------------
 server1
(1 row)

$ ps aux|grep server1
postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: server1: background writer
...
</screen>
  </para>

  <para>
   If you have turned off <xref linkend="guc-update-process-title"/> then the
   activity indicator is not updated; the process title is set only once
   when a new process is launched.  On some platforms this saves a measurable
   amount of per-command overhead;  on others it's insignificant.
  </para>

  <tip>
  <para>
  <productname>Solaris</productname> requires special handling. You must
  use <command>/usr/ucb/ps</command>, rather than
  <command>/bin/ps</command>. You also must use two <option>w</option>
  flags, not just one. In addition, your original invocation of the
  <command>postgres</command> command must have a shorter
  <command>ps</command> status display than that provided by each
  server process.  If you fail to do all three things, the <command>ps</command>
  output for each server process will be the original <command>postgres</command>
  command line.
  </para>
  </tip>
 </sect1>

 <sect1 id="monitoring-stats">
  <title>The Statistics Collector</title>

  <indexterm zone="monitoring-stats">
   <primary>statistics</primary>
  </indexterm>

  <para>
   <productname>PostgreSQL</productname>'s <firstterm>statistics collector</firstterm>
   is a subsystem that supports collection and reporting of information about
   server activity.  Presently, the collector can count accesses to tables
   and indexes in both disk-block and individual-row terms.  It also tracks
   the total number of rows in each table, and information about vacuum and
   analyze actions for each table.  It can also count calls to user-defined
   functions and the total time spent in each one.
  </para>

  <para>
   <productname>PostgreSQL</productname> also supports reporting dynamic
   information about exactly what is going on in the system right now, such as
   the exact command currently being executed by other server processes, and
   which other connections exist in the system.  This facility is independent
   of the collector process.
  </para>

 <sect2 id="monitoring-stats-setup">
  <title>Statistics Collection Configuration</title>

  <para>
   Since collection of statistics adds some overhead to query execution,
   the system can be configured to collect or not collect information.
   This is controlled by configuration parameters that are normally set in
   <filename>postgresql.conf</filename>.  (See <xref linkend="runtime-config"/> for
   details about setting configuration parameters.)
  </para>

  <para>
   The parameter <xref linkend="guc-track-activities"/> enables monitoring
   of the current command being executed by any server process.
  </para>

  <para>
   The parameter <xref linkend="guc-track-counts"/> controls whether
   statistics are collected about table and index accesses.
  </para>

  <para>
   The parameter <xref linkend="guc-track-functions"/> enables tracking of
   usage of user-defined functions.
  </para>

  <para>
   The parameter <xref linkend="guc-track-io-timing"/> enables monitoring
   of block read and write times.
  </para>

  <para>
   Normally these parameters are set in <filename>postgresql.conf</filename> so
   that they apply to all server processes, but it is possible to turn
   them on or off in individual sessions using the <xref
   linkend="sql-set"/> command. (To prevent
   ordinary users from hiding their activity from the administrator,
   only superusers are allowed to change these parameters with
   <command>SET</command>.)
  </para>

  <para>
   The statistics collector transmits the collected information to other
   <productname>PostgreSQL</productname> processes through temporary files.
   These files are stored in the directory named by the
   <xref linkend="guc-stats-temp-directory"/> parameter,
   <filename>pg_stat_tmp</filename> by default.
   For better performance, <varname>stats_temp_directory</varname> can be
   pointed at a RAM-based file system, decreasing physical I/O requirements.
   When the server shuts down cleanly, a permanent copy of the statistics
   data is stored in the <filename>pg_stat</filename> subdirectory, so that
   statistics can be retained across server restarts.  When recovery is
   performed at server start (e.g., after immediate shutdown, server crash,
   and point-in-time recovery), all statistics counters are reset.
  </para>

 </sect2>

 <sect2 id="monitoring-stats-views">
  <title>Viewing Statistics</title>

  <para>
   Several predefined views, listed in <xref
   linkend="monitoring-stats-dynamic-views-table"/>, are available to show
   the current state of the system. There are also several other
   views, listed in <xref
   linkend="monitoring-stats-views-table"/>, available to show the results
   of statistics collection.  Alternatively, one can
   build custom views using the underlying statistics functions, as discussed
   in <xref linkend="monitoring-stats-functions"/>.
  </para>

  <para>
   When using the statistics to monitor collected data, it is important
   to realize that the information does not update instantaneously.
   Each individual server process transmits new statistical counts to
   the collector just before going idle; so a query or transaction still in
   progress does not affect the displayed totals.  Also, the collector itself
   emits a new report at most once per <varname>PGSTAT_STAT_INTERVAL</varname>
   milliseconds (500 ms unless altered while building the server).  So the
   displayed information lags behind actual activity.  However, current-query
   information collected by <varname>track_activities</varname> is
   always up-to-date.
  </para>

  <para>
   Another important point is that when a server process is asked to display
   any of these statistics, it first fetches the most recent report emitted by
   the collector process and then continues to use this snapshot for all
   statistical views and functions until the end of its current transaction.
   So the statistics will show static information as long as you continue the
   current transaction.  Similarly, information about the current queries of
   all sessions is collected when any such information is first requested
   within a transaction, and the same information will be displayed throughout
   the transaction.
   This is a feature, not a bug, because it allows you to perform several
   queries on the statistics and correlate the results without worrying that
   the numbers are changing underneath you.  But if you want to see new
   results with each query, be sure to do the queries outside any transaction
   block.  Alternatively, you can invoke
   <function>pg_stat_clear_snapshot</function>(), which will discard the
   current transaction's statistics snapshot (if any).  The next use of
   statistical information will cause a new snapshot to be fetched.
  </para>

  <para>
   A transaction can also see its own statistics (as yet untransmitted to the
   collector) in the views <structname>pg_stat_xact_all_tables</structname>,
   <structname>pg_stat_xact_sys_tables</structname>,
   <structname>pg_stat_xact_user_tables</structname>, and
   <structname>pg_stat_xact_user_functions</structname>.  These numbers do not act as
   stated above; instead they update continuously throughout the transaction.
  </para>

  <para>
   Some of the information in the dynamic statistics views shown in <xref
   linkend="monitoring-stats-dynamic-views-table"/> is security restricted.
   Ordinary users can only see all the information about their own sessions
   (sessions belonging to a role that they are a member of).  In rows about
   other sessions, many columns will be null.  Note, however, that the
   existence of a session and its general properties such as its sessions user
   and database are visible to all users.  Superusers and members of the
   built-in role <literal>pg_read_all_stats</literal> (see also <xref
   linkend="default-roles"/>) can see all the information about all sessions.
  </para>

  <table id="monitoring-stats-dynamic-views-table">
   <title>Dynamic Statistics Views</title>

   <tgroup cols="2">
    <thead>
     <row>
      <entry>View Name</entry>
      <entry>Description</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry>
       <structname>pg_stat_activity</structname>
       <indexterm><primary>pg_stat_activity</primary></indexterm>
      </entry>
      <entry>
       One row per server process, showing information related to
       the current activity of that process, such as state and current query.
       See <link linkend="monitoring-pg-stat-activity-view">
       <structname>pg_stat_activity</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_replication</structname><indexterm><primary>pg_stat_replication</primary></indexterm></entry>
      <entry>One row per WAL sender process, showing statistics about
       replication to that sender's connected standby server.
       See <link linkend="monitoring-pg-stat-replication-view">
       <structname>pg_stat_replication</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_replication_slots</structname><indexterm><primary>pg_stat_replication_slots</primary></indexterm></entry>
      <entry>One row per replication slot, showing statistics about
       replication slot usage.
       See <link linkend="monitoring-pg-stat-replication-slots-view">
       <structname>pg_stat_replication_slots</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_wal_receiver</structname><indexterm><primary>pg_stat_wal_receiver</primary></indexterm></entry>
      <entry>Only one row, showing statistics about the WAL receiver from
       that receiver's connected server.
       See <link linkend="monitoring-pg-stat-wal-receiver-view">
       <structname>pg_stat_wal_receiver</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_subscription</structname><indexterm><primary>pg_stat_subscription</primary></indexterm></entry>
      <entry>At least one row per subscription, showing information about
       the subscription workers.
       See <link linkend="monitoring-pg-stat-subscription">
       <structname>pg_stat_subscription</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_ssl</structname><indexterm><primary>pg_stat_ssl</primary></indexterm></entry>
      <entry>One row per connection (regular and replication), showing information about
       SSL used on this connection.
       See <link linkend="monitoring-pg-stat-ssl-view">
       <structname>pg_stat_ssl</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_gssapi</structname><indexterm><primary>pg_stat_gssapi</primary></indexterm></entry>
      <entry>One row per connection (regular and replication), showing information about
       GSSAPI authentication and encryption used on this connection.
       See <link linkend="monitoring-pg-stat-gssapi-view">
       <structname>pg_stat_gssapi</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_progress_analyze</structname><indexterm><primary>pg_stat_progress_analyze</primary></indexterm></entry>
      <entry>One row for each backend (including autovacuum worker processes) running
       <command>ANALYZE</command>, showing current progress.
       See <xref linkend='analyze-progress-reporting'/>.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_progress_create_index</structname><indexterm><primary>pg_stat_progress_create_index</primary></indexterm></entry>
      <entry>One row for each backend running <command>CREATE INDEX</command> or <command>REINDEX</command>, showing
      current progress.
      See <xref linkend='create-index-progress-reporting'/>.
     </entry>
     </row>

     <row>
      <entry><structname>pg_stat_progress_vacuum</structname><indexterm><primary>pg_stat_progress_vacuum</primary></indexterm></entry>
      <entry>One row for each backend (including autovacuum worker processes) running
       <command>VACUUM</command>, showing current progress.
       See <xref linkend='vacuum-progress-reporting'/>.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_progress_cluster</structname><indexterm><primary>pg_stat_progress_cluster</primary></indexterm></entry>
      <entry>One row for each backend running
       <command>CLUSTER</command> or <command>VACUUM FULL</command>, showing current progress.
       See <xref linkend='cluster-progress-reporting'/>.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_progress_basebackup</structname><indexterm><primary>pg_stat_progress_basebackup</primary></indexterm></entry>
      <entry>One row for each WAL sender process streaming a base backup,
       showing current progress.
       See <xref linkend='basebackup-progress-reporting'/>.
      </entry>
     </row>

    </tbody>
   </tgroup>
  </table>

  <table id="monitoring-stats-views-table">
   <title>Collected Statistics Views</title>

   <tgroup cols="2">
    <thead>
     <row>
      <entry>View Name</entry>
      <entry>Description</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><structname>pg_stat_archiver</structname><indexterm><primary>pg_stat_archiver</primary></indexterm></entry>
      <entry>One row only, showing statistics about the
       WAL archiver process's activity. See
       <link linkend="monitoring-pg-stat-archiver-view">
       <structname>pg_stat_archiver</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_bgwriter</structname><indexterm><primary>pg_stat_bgwriter</primary></indexterm></entry>
      <entry>One row only, showing statistics about the
       background writer process's activity. See
       <link linkend="monitoring-pg-stat-bgwriter-view">
       <structname>pg_stat_bgwriter</structname></link> for details.
     </entry>
     </row>

     <row>
      <entry><structname>pg_stat_wal</structname><indexterm><primary>pg_stat_wal</primary></indexterm></entry>
      <entry>One row only, showing statistics about WAL activity. See
       <link linkend="monitoring-pg-stat-wal-view">
       <structname>pg_stat_wal</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_database</structname><indexterm><primary>pg_stat_database</primary></indexterm></entry>
      <entry>One row per database, showing database-wide statistics. See
       <link linkend="monitoring-pg-stat-database-view">
       <structname>pg_stat_database</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_database_conflicts</structname><indexterm><primary>pg_stat_database_conflicts</primary></indexterm></entry>
      <entry>
       One row per database, showing database-wide statistics about
       query cancels due to conflict with recovery on standby servers.
       See <link linkend="monitoring-pg-stat-database-conflicts-view">
       <structname>pg_stat_database_conflicts</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_all_tables</structname><indexterm><primary>pg_stat_all_tables</primary></indexterm></entry>
      <entry>
       One row for each table in the current database, showing statistics
       about accesses to that specific table.
       See <link linkend="monitoring-pg-stat-all-tables-view">
       <structname>pg_stat_all_tables</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_sys_tables</structname><indexterm><primary>pg_stat_sys_tables</primary></indexterm></entry>
      <entry>Same as <structname>pg_stat_all_tables</structname>, except that only
      system tables are shown.</entry>
     </row>

     <row>
      <entry><structname>pg_stat_user_tables</structname><indexterm><primary>pg_stat_user_tables</primary></indexterm></entry>
      <entry>Same as <structname>pg_stat_all_tables</structname>, except that only user
      tables are shown.</entry>
     </row>

     <row>
      <entry><structname>pg_stat_xact_all_tables</structname><indexterm><primary>pg_stat_xact_all_tables</primary></indexterm></entry>
      <entry>Similar to <structname>pg_stat_all_tables</structname>, but counts actions
      taken so far within the current transaction (which are <emphasis>not</emphasis>
      yet included in <structname>pg_stat_all_tables</structname> and related views).
      The columns for numbers of live and dead rows and vacuum and
      analyze actions are not present in this view.</entry>
     </row>

     <row>
      <entry><structname>pg_stat_xact_sys_tables</structname><indexterm><primary>pg_stat_xact_sys_tables</primary></indexterm></entry>
      <entry>Same as <structname>pg_stat_xact_all_tables</structname>, except that only
      system tables are shown.</entry>
     </row>

     <row>
      <entry><structname>pg_stat_xact_user_tables</structname><indexterm><primary>pg_stat_xact_user_tables</primary></indexterm></entry>
      <entry>Same as <structname>pg_stat_xact_all_tables</structname>, except that only
      user tables are shown.</entry>
     </row>

     <row>
      <entry><structname>pg_stat_all_indexes</structname><indexterm><primary>pg_stat_all_indexes</primary></indexterm></entry>
      <entry>
       One row for each index in the current database, showing statistics
       about accesses to that specific index.
       See <link linkend="monitoring-pg-stat-all-indexes-view">
       <structname>pg_stat_all_indexes</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_sys_indexes</structname><indexterm><primary>pg_stat_sys_indexes</primary></indexterm></entry>
      <entry>Same as <structname>pg_stat_all_indexes</structname>, except that only
      indexes on system tables are shown.</entry>
     </row>

     <row>
      <entry><structname>pg_stat_user_indexes</structname><indexterm><primary>pg_stat_user_indexes</primary></indexterm></entry>
      <entry>Same as <structname>pg_stat_all_indexes</structname>, except that only
      indexes on user tables are shown.</entry>
     </row>

     <row>
      <entry><structname>pg_statio_all_tables</structname><indexterm><primary>pg_statio_all_tables</primary></indexterm></entry>
      <entry>
       One row for each table in the current database, showing statistics
       about I/O on that specific table.
       See <link linkend="monitoring-pg-statio-all-tables-view">
       <structname>pg_statio_all_tables</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_statio_sys_tables</structname><indexterm><primary>pg_statio_sys_tables</primary></indexterm></entry>
      <entry>Same as <structname>pg_statio_all_tables</structname>, except that only
      system tables are shown.</entry>
     </row>

     <row>
      <entry><structname>pg_statio_user_tables</structname><indexterm><primary>pg_statio_user_tables</primary></indexterm></entry>
      <entry>Same as <structname>pg_statio_all_tables</structname>, except that only
      user tables are shown.</entry>
     </row>

     <row>
      <entry><structname>pg_statio_all_indexes</structname><indexterm><primary>pg_statio_all_indexes</primary></indexterm></entry>
      <entry>
       One row for each index in the current database,
       showing statistics about I/O on that specific index.
       See <link linkend="monitoring-pg-statio-all-indexes-view">
       <structname>pg_statio_all_indexes</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_statio_sys_indexes</structname><indexterm><primary>pg_statio_sys_indexes</primary></indexterm></entry>
      <entry>Same as <structname>pg_statio_all_indexes</structname>, except that only
      indexes on system tables are shown.</entry>
     </row>

     <row>
      <entry><structname>pg_statio_user_indexes</structname><indexterm><primary>pg_statio_user_indexes</primary></indexterm></entry>
      <entry>Same as <structname>pg_statio_all_indexes</structname>, except that only
      indexes on user tables are shown.</entry>
     </row>

     <row>
      <entry><structname>pg_statio_all_sequences</structname><indexterm><primary>pg_statio_all_sequences</primary></indexterm></entry>
     <entry>
       One row for each sequence in the current database,
       showing statistics about I/O on that specific sequence.
       See <link linkend="monitoring-pg-statio-all-sequences-view">
       <structname>pg_statio_all_sequences</structname></link> for details.
     </entry>
     </row>

     <row>
      <entry><structname>pg_statio_sys_sequences</structname><indexterm><primary>pg_statio_sys_sequences</primary></indexterm></entry>
      <entry>Same as <structname>pg_statio_all_sequences</structname>, except that only
      system sequences are shown.  (Presently, no system sequences are defined,
      so this view is always empty.)</entry>
     </row>

     <row>
      <entry><structname>pg_statio_user_sequences</structname><indexterm><primary>pg_statio_user_sequences</primary></indexterm></entry>
      <entry>Same as <structname>pg_statio_all_sequences</structname>, except that only
      user sequences are shown.</entry>
     </row>

     <row>
      <entry><structname>pg_stat_user_functions</structname><indexterm><primary>pg_stat_user_functions</primary></indexterm></entry>
      <entry>
       One row for each tracked function, showing statistics
       about executions of that function. See
       <link linkend="monitoring-pg-stat-user-functions-view">
       <structname>pg_stat_user_functions</structname></link> for details.
      </entry>
     </row>

     <row>
      <entry><structname>pg_stat_xact_user_functions</structname><indexterm><primary>pg_stat_xact_user_functions</primary></indexterm></entry>
      <entry>Similar to <structname>pg_stat_user_functions</structname>, but counts only
      calls during the current transaction (which are <emphasis>not</emphasis>
      yet included in <structname>pg_stat_user_functions</structname>).</entry>
     </row>

     <row>
      <entry><structname>pg_stat_slru</structname><indexterm><primary>pg_stat_slru</primary></indexterm></entry>
      <entry>One row per SLRU, showing statistics of operations. See
       <link linkend="monitoring-pg-stat-slru-view">
       <structname>pg_stat_slru</structname></link> for details.
      </entry>
     </row>

    </tbody>
   </tgroup>
  </table>

  <para>
   The per-index statistics are particularly useful to determine which
   indexes are being used and how effective they are.
  </para>

  <para>
   The <structname>pg_statio_</structname> views are primarily useful to
   determine the effectiveness of the buffer cache.  When the number
   of actual disk reads is much smaller than the number of buffer
   hits, then the cache is satisfying most read requests without
   invoking a kernel call. However, these statistics do not give the
   entire story: due to the way in which <productname>PostgreSQL</productname>
   handles disk I/O, data that is not in the
   <productname>PostgreSQL</productname> buffer cache might still reside in the
   kernel's I/O cache, and might therefore still be fetched without
   requiring a physical read. Users interested in obtaining more
   detailed information on <productname>PostgreSQL</productname> I/O behavior are
   advised to use the <productname>PostgreSQL</productname> statistics collector
   in combination with operating system utilities that allow insight
   into the kernel's handling of I/O.
  </para>

 </sect2>

 <sect2 id="monitoring-pg-stat-activity-view">
  <title><structname>pg_stat_activity</structname></title>

  <indexterm>
   <primary>pg_stat_activity</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_activity</structname> view will have one row
   per server process, showing information related to
   the current activity of that process.
  </para>

  <table id="pg-stat-activity-view" xreflabel="pg_stat_activity">
   <title><structname>pg_stat_activity</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the database this backend is connected to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datname</structfield> <type>name</type>
      </para>
      <para>
       Name of the database this backend is connected to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of this backend
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>leader_pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of the parallel group leader, if this process is a
       parallel query worker.  <literal>NULL</literal> if this process is a
       parallel group leader or does not participate in parallel query.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usesysid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the user logged into this backend
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usename</structfield> <type>name</type>
      </para>
      <para>
       Name of the user logged into this backend
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>application_name</structfield> <type>text</type>
      </para>
      <para>
       Name of the application that is connected
       to this backend
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>client_addr</structfield> <type>inet</type>
      </para>
      <para>
       IP address of the client connected to this backend.
       If this field is null, it indicates either that the client is
       connected via a Unix socket on the server machine or that this is an
       internal process such as autovacuum.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>client_hostname</structfield> <type>text</type>
      </para>
      <para>
       Host name of the connected client, as reported by a
       reverse DNS lookup of <structfield>client_addr</structfield>. This field will
       only be non-null for IP connections, and only when <xref linkend="guc-log-hostname"/> is enabled.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>client_port</structfield> <type>integer</type>
      </para>
      <para>
       TCP port number that the client is using for communication
       with this backend, or <literal>-1</literal> if a Unix socket is used.
       If this field is null, it indicates that this is an internal server process.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>backend_start</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time when this process was started.  For client backends,
       this is the time the client connected to the server.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>xact_start</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time when this process' current transaction was started, or null
       if no transaction is active. If the current
       query is the first of its transaction, this column is equal to the
       <structfield>query_start</structfield> column.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>query_start</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time when the currently active query was started, or if
       <structfield>state</structfield> is not <literal>active</literal>, when the last query
       was started
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>state_change</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time when the <structfield>state</structfield> was last changed
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>wait_event_type</structfield> <type>text</type>
      </para>
      <para>
       The type of event for which the backend is waiting, if any;
       otherwise NULL.  See <xref linkend="wait-event-table"/>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>wait_event</structfield> <type>text</type>
      </para>
      <para>
       Wait event name if backend is currently waiting, otherwise NULL.
       See <xref linkend="wait-event-activity-table"/> through
       <xref linkend="wait-event-timeout-table"/>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>state</structfield> <type>text</type>
      </para>
      <para>
       Current overall state of this backend.
       Possible values are:
       <itemizedlist>
        <listitem>
        <para>
          <literal>active</literal>: The backend is executing a query.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>idle</literal>: The backend is waiting for a new client command.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>idle in transaction</literal>: The backend is in a transaction,
          but is not currently executing a query.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>idle in transaction (aborted)</literal>: This state is similar to
          <literal>idle in transaction</literal>, except one of the statements in
          the transaction caused an error.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>fastpath function call</literal>: The backend is executing a
          fast-path function.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>disabled</literal>: This state is reported if <xref linkend="guc-track-activities"/> is disabled in this backend.
         </para>
       </listitem>
       </itemizedlist>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>backend_xid</structfield> <type>xid</type>
      </para>
      <para>
       Top-level transaction identifier of this backend, if any.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>backend_xmin</structfield> <type>xid</type>
      </para>
      <para>
       The current backend's <literal>xmin</literal> horizon.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>query</structfield> <type>text</type>
      </para>
      <para>
       Text of this backend's most recent query. If
       <structfield>state</structfield> is <literal>active</literal> this field shows the
       currently executing query. In all other states, it shows the last query
       that was executed. By default the query text is truncated at 1024
       bytes; this value can be changed via the parameter
       <xref linkend="guc-track-activity-query-size"/>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>backend_type</structfield> <type>text</type>
      </para>
      <para>
       Type of current backend. Possible types are
       <literal>autovacuum launcher</literal>, <literal>autovacuum worker</literal>,
       <literal>logical replication launcher</literal>,
       <literal>logical replication worker</literal>,
       <literal>parallel worker</literal>, <literal>background writer</literal>,
       <literal>client backend</literal>, <literal>checkpointer</literal>,
       <literal>startup</literal>, <literal>walreceiver</literal>,
       <literal>walsender</literal> and <literal>walwriter</literal>.
       In addition, background workers registered by extensions may have
       additional types.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <note>
   <para>
    The <structfield>wait_event</structfield> and <structfield>state</structfield> columns are
    independent.  If a backend is in the <literal>active</literal> state,
    it may or may not be <literal>waiting</literal> on some event.  If the state
    is <literal>active</literal> and <structfield>wait_event</structfield> is non-null, it
    means that a query is being executed, but is being blocked somewhere
    in the system.
   </para>
  </note>

  <table id="wait-event-table">
   <title>Wait Event Types</title>
   <tgroup cols="2">
    <thead>
     <row>
      <entry>Wait Event Type</entry>
      <entry>Description</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><literal>Activity</literal></entry>
      <entry>The server process is idle.  This event type indicates a process
       waiting for activity in its main processing loop.
       <literal>wait_event</literal> will identify the specific wait point;
       see <xref linkend="wait-event-activity-table"/>.
      </entry>
     </row>
     <row>
      <entry><literal>BufferPin</literal></entry>
      <entry>The server process is waiting for exclusive access to
       a data buffer.  Buffer pin waits can be protracted if
       another process holds an open cursor that last read data from the
       buffer in question. See <xref linkend="wait-event-bufferpin-table"/>.
      </entry>
     </row>
     <row>
      <entry><literal>Client</literal></entry>
      <entry>The server process is waiting for activity on a socket
       connected to a user application.  Thus, the server expects something
       to happen that is independent of its internal processes.
       <literal>wait_event</literal> will identify the specific wait point;
       see <xref linkend="wait-event-client-table"/>.
      </entry>
     </row>
     <row>
      <entry><literal>Extension</literal></entry>
      <entry>The server process is waiting for some condition defined by an
       extension module.
       See <xref linkend="wait-event-extension-table"/>.
      </entry>
     </row>
     <row>
      <entry><literal>IO</literal></entry>
      <entry>The server process is waiting for an I/O operation to complete.
       <literal>wait_event</literal> will identify the specific wait point;
       see <xref linkend="wait-event-io-table"/>.
      </entry>
     </row>
     <row>
      <entry><literal>IPC</literal></entry>
      <entry>The server process is waiting for some interaction with
       another server process.  <literal>wait_event</literal> will
       identify the specific wait point;
       see <xref linkend="wait-event-ipc-table"/>.
      </entry>
     </row>
     <row>
      <entry><literal>Lock</literal></entry>
      <entry>The server process is waiting for a heavyweight lock.
       Heavyweight locks, also known as lock manager locks or simply locks,
       primarily protect SQL-visible objects such as tables.  However,
       they are also used to ensure mutual exclusion for certain internal
       operations such as relation extension.  <literal>wait_event</literal>
       will identify the type of lock awaited;
       see <xref linkend="wait-event-lock-table"/>.
      </entry>
     </row>
     <row>
      <entry><literal>LWLock</literal></entry>
      <entry> The server process is waiting for a lightweight lock.
       Most such locks protect a particular data structure in shared memory.
       <literal>wait_event</literal> will contain a name identifying the purpose
       of the lightweight lock.  (Some locks have specific names; others
       are part of a group of locks each with a similar purpose.)
       See <xref linkend="wait-event-lwlock-table"/>.
      </entry>
     </row>
     <row>
      <entry><literal>Timeout</literal></entry>
      <entry>The server process is waiting for a timeout
       to expire.  <literal>wait_event</literal> will identify the specific wait
       point; see <xref linkend="wait-event-timeout-table"/>.
      </entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="wait-event-activity-table">
   <title>Wait Events of Type <literal>Activity</literal></title>
   <tgroup cols="2">
    <thead>
     <row>
      <entry><literal>Activity</literal> Wait Event</entry>
      <entry>Description</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><literal>ArchiverMain</literal></entry>
      <entry>Waiting in main loop of archiver process.</entry>
     </row>
     <row>
      <entry><literal>AutoVacuumMain</literal></entry>
      <entry>Waiting in main loop of autovacuum launcher process.</entry>
     </row>
     <row>
      <entry><literal>BgWriterHibernate</literal></entry>
      <entry>Waiting in background writer process, hibernating.</entry>
     </row>
     <row>
      <entry><literal>BgWriterMain</literal></entry>
      <entry>Waiting in main loop of background writer process.</entry>
     </row>
     <row>
      <entry><literal>CheckpointerMain</literal></entry>
      <entry>Waiting in main loop of checkpointer process.</entry>
     </row>
     <row>
      <entry><literal>LogicalApplyMain</literal></entry>
      <entry>Waiting in main loop of logical replication apply process.</entry>
     </row>
     <row>
      <entry><literal>LogicalLauncherMain</literal></entry>
      <entry>Waiting in main loop of logical replication launcher process.</entry>
     </row>
     <row>
      <entry><literal>PgStatMain</literal></entry>
      <entry>Waiting in main loop of statistics collector process.</entry>
     </row>
     <row>
      <entry><literal>RecoveryWalStream</literal></entry>
      <entry>Waiting in main loop of startup process for WAL to arrive, during
       streaming recovery.</entry>
     </row>
     <row>
      <entry><literal>SysLoggerMain</literal></entry>
      <entry>Waiting in main loop of syslogger process.</entry>
     </row>
     <row>
      <entry><literal>WalReceiverMain</literal></entry>
      <entry>Waiting in main loop of WAL receiver process.</entry>
     </row>
     <row>
      <entry><literal>WalSenderMain</literal></entry>
      <entry>Waiting in main loop of WAL sender process.</entry>
     </row>
     <row>
      <entry><literal>WalWriterMain</literal></entry>
      <entry>Waiting in main loop of WAL writer process.</entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="wait-event-bufferpin-table">
   <title>Wait Events of Type <literal>BufferPin</literal></title>
   <tgroup cols="2">
    <thead>
     <row>
      <entry><literal>BufferPin</literal> Wait Event</entry>
      <entry>Description</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><literal>BufferPin</literal></entry>
      <entry>Waiting to acquire an exclusive pin on a buffer.</entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="wait-event-client-table">
   <title>Wait Events of Type <literal>Client</literal></title>
   <tgroup cols="2">
    <thead>
     <row>
      <entry><literal>Client</literal> Wait Event</entry>
      <entry>Description</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><literal>ClientRead</literal></entry>
      <entry>Waiting to read data from the client.</entry>
     </row>
     <row>
      <entry><literal>ClientWrite</literal></entry>
      <entry>Waiting to write data to the client.</entry>
     </row>
     <row>
      <entry><literal>GSSOpenServer</literal></entry>
      <entry>Waiting to read data from the client while establishing a GSSAPI
       session.</entry>
     </row>
     <row>
      <entry><literal>LibPQWalReceiverConnect</literal></entry>
      <entry>Waiting in WAL receiver to establish connection to remote
       server.</entry>
     </row>
     <row>
      <entry><literal>LibPQWalReceiverReceive</literal></entry>
      <entry>Waiting in WAL receiver to receive data from remote server.</entry>
     </row>
     <row>
      <entry><literal>SSLOpenServer</literal></entry>
      <entry>Waiting for SSL while attempting connection.</entry>
     </row>
     <row>
      <entry><literal>WalReceiverWaitStart</literal></entry>
      <entry>Waiting for startup process to send initial data for streaming
       replication.</entry>
     </row>
     <row>
      <entry><literal>WalSenderWaitForWAL</literal></entry>
      <entry>Waiting for WAL to be flushed in WAL sender process.</entry>
     </row>
     <row>
      <entry><literal>WalSenderWriteData</literal></entry>
      <entry>Waiting for any activity when processing replies from WAL
       receiver in WAL sender process.</entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="wait-event-extension-table">
   <title>Wait Events of Type <literal>Extension</literal></title>
   <tgroup cols="2">
    <thead>
     <row>
      <entry><literal>Extension</literal> Wait Event</entry>
      <entry>Description</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><literal>Extension</literal></entry>
      <entry>Waiting in an extension.</entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="wait-event-io-table">
   <title>Wait Events of Type <literal>IO</literal></title>
   <tgroup cols="2">
    <thead>
     <row>
      <entry><literal>IO</literal> Wait Event</entry>
      <entry>Description</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><literal>BaseBackupRead</literal></entry>
      <entry>Waiting for base backup to read from a file.</entry>
     </row>
     <row>
      <entry><literal>BufFileRead</literal></entry>
      <entry>Waiting for a read from a buffered file.</entry>
     </row>
     <row>
      <entry><literal>BufFileWrite</literal></entry>
      <entry>Waiting for a write to a buffered file.</entry>
     </row>
     <row>
      <entry><literal>BufFileTruncate</literal></entry>
      <entry>Waiting for a buffered file to be truncated.</entry>
     </row>
     <row>
      <entry><literal>ControlFileRead</literal></entry>
      <entry>Waiting for a read from the <filename>pg_control</filename>
       file.</entry>
     </row>
     <row>
      <entry><literal>ControlFileSync</literal></entry>
      <entry>Waiting for the <filename>pg_control</filename> file to reach
       durable storage.</entry>
     </row>
     <row>
      <entry><literal>ControlFileSyncUpdate</literal></entry>
      <entry>Waiting for an update to the <filename>pg_control</filename> file
       to reach durable storage.</entry>
     </row>
     <row>
      <entry><literal>ControlFileWrite</literal></entry>
      <entry>Waiting for a write to the <filename>pg_control</filename>
       file.</entry>
     </row>
     <row>
      <entry><literal>ControlFileWriteUpdate</literal></entry>
      <entry>Waiting for a write to update the <filename>pg_control</filename>
       file.</entry>
     </row>
     <row>
      <entry><literal>CopyFileRead</literal></entry>
      <entry>Waiting for a read during a file copy operation.</entry>
     </row>
     <row>
      <entry><literal>CopyFileWrite</literal></entry>
      <entry>Waiting for a write during a file copy operation.</entry>
     </row>
     <row>
      <entry><literal>DSMFillZeroWrite</literal></entry>
      <entry>Waiting to fill a dynamic shared memory backing file with
       zeroes.</entry>
     </row>
     <row>
      <entry><literal>DataFileExtend</literal></entry>
      <entry>Waiting for a relation data file to be extended.</entry>
     </row>
     <row>
      <entry><literal>DataFileFlush</literal></entry>
      <entry>Waiting for a relation data file to reach durable storage.</entry>
     </row>
     <row>
      <entry><literal>DataFileImmediateSync</literal></entry>
      <entry>Waiting for an immediate synchronization of a relation data file to
       durable storage.</entry>
     </row>
     <row>
      <entry><literal>DataFilePrefetch</literal></entry>
      <entry>Waiting for an asynchronous prefetch from a relation data
       file.</entry>
     </row>
     <row>
      <entry><literal>DataFileRead</literal></entry>
      <entry>Waiting for a read from a relation data file.</entry>
     </row>
     <row>
      <entry><literal>DataFileSync</literal></entry>
      <entry>Waiting for changes to a relation data file to reach durable storage.</entry>
     </row>
     <row>
      <entry><literal>DataFileTruncate</literal></entry>
      <entry>Waiting for a relation data file to be truncated.</entry>
     </row>
     <row>
      <entry><literal>DataFileWrite</literal></entry>
      <entry>Waiting for a write to a relation data file.</entry>
     </row>
     <row>
      <entry><literal>LockFileAddToDataDirRead</literal></entry>
      <entry>Waiting for a read while adding a line to the data directory lock
       file.</entry>
     </row>
     <row>
      <entry><literal>LockFileAddToDataDirSync</literal></entry>
      <entry>Waiting for data to reach durable storage while adding a line to the
       data directory lock file.</entry>
     </row>
     <row>
      <entry><literal>LockFileAddToDataDirWrite</literal></entry>
      <entry>Waiting for a write while adding a line to the data directory
       lock file.</entry>
     </row>
     <row>
      <entry><literal>LockFileCreateRead</literal></entry>
      <entry>Waiting to read while creating the data directory lock
       file.</entry>
     </row>
     <row>
      <entry><literal>LockFileCreateSync</literal></entry>
      <entry>Waiting for data to reach durable storage while creating the data
       directory lock file.</entry>
     </row>
     <row>
      <entry><literal>LockFileCreateWrite</literal></entry>
      <entry>Waiting for a write while creating the data directory lock
       file.</entry>
     </row>
     <row>
      <entry><literal>LockFileReCheckDataDirRead</literal></entry>
      <entry>Waiting for a read during recheck of the data directory lock
       file.</entry>
     </row>
     <row>
      <entry><literal>LogicalRewriteCheckpointSync</literal></entry>
      <entry>Waiting for logical rewrite mappings to reach durable storage
       during a checkpoint.</entry>
     </row>
     <row>
      <entry><literal>LogicalRewriteMappingSync</literal></entry>
      <entry>Waiting for mapping data to reach durable storage during a logical
       rewrite.</entry>
     </row>
     <row>
      <entry><literal>LogicalRewriteMappingWrite</literal></entry>
      <entry>Waiting for a write of mapping data during a logical
       rewrite.</entry>
     </row>
     <row>
      <entry><literal>LogicalRewriteSync</literal></entry>
      <entry>Waiting for logical rewrite mappings to reach durable
       storage.</entry>
     </row>
     <row>
      <entry><literal>LogicalRewriteTruncate</literal></entry>
      <entry>Waiting for truncate of mapping data during a logical
       rewrite.</entry>
     </row>
     <row>
      <entry><literal>LogicalRewriteWrite</literal></entry>
      <entry>Waiting for a write of logical rewrite mappings.</entry>
     </row>
     <row>
      <entry><literal>RelationMapRead</literal></entry>
      <entry>Waiting for a read of the relation map file.</entry>
     </row>
     <row>
      <entry><literal>RelationMapSync</literal></entry>
      <entry>Waiting for the relation map file to reach durable storage.</entry>
     </row>
     <row>
      <entry><literal>RelationMapWrite</literal></entry>
      <entry>Waiting for a write to the relation map file.</entry>
     </row>
     <row>
      <entry><literal>ReorderBufferRead</literal></entry>
      <entry>Waiting for a read during reorder buffer management.</entry>
     </row>
     <row>
      <entry><literal>ReorderBufferWrite</literal></entry>
      <entry>Waiting for a write during reorder buffer management.</entry>
     </row>
     <row>
      <entry><literal>ReorderLogicalMappingRead</literal></entry>
      <entry>Waiting for a read of a logical mapping during reorder buffer
       management.</entry>
     </row>
     <row>
      <entry><literal>ReplicationSlotRead</literal></entry>
      <entry>Waiting for a read from a replication slot control file.</entry>
     </row>
     <row>
      <entry><literal>ReplicationSlotRestoreSync</literal></entry>
      <entry>Waiting for a replication slot control file to reach durable storage
       while restoring it to memory.</entry>
     </row>
     <row>
      <entry><literal>ReplicationSlotSync</literal></entry>
      <entry>Waiting for a replication slot control file to reach durable
       storage.</entry>
     </row>
     <row>
      <entry><literal>ReplicationSlotWrite</literal></entry>
      <entry>Waiting for a write to a replication slot control file.</entry>
     </row>
     <row>
      <entry><literal>SLRUFlushSync</literal></entry>
      <entry>Waiting for SLRU data to reach durable storage during a checkpoint
       or database shutdown.</entry>
     </row>
     <row>
      <entry><literal>SLRURead</literal></entry>
      <entry>Waiting for a read of an SLRU page.</entry>
     </row>
     <row>
      <entry><literal>SLRUSync</literal></entry>
      <entry>Waiting for SLRU data to reach durable storage following a page
       write.</entry>
     </row>
     <row>
      <entry><literal>SLRUWrite</literal></entry>
      <entry>Waiting for a write of an SLRU page.</entry>
     </row>
     <row>
      <entry><literal>SnapbuildRead</literal></entry>
      <entry>Waiting for a read of a serialized historical catalog
       snapshot.</entry>
     </row>
     <row>
      <entry><literal>SnapbuildSync</literal></entry>
      <entry>Waiting for a serialized historical catalog snapshot to reach
       durable storage.</entry>
     </row>
     <row>
      <entry><literal>SnapbuildWrite</literal></entry>
      <entry>Waiting for a write of a serialized historical catalog
       snapshot.</entry>
     </row>
     <row>
      <entry><literal>TimelineHistoryFileSync</literal></entry>
      <entry>Waiting for a timeline history file received via streaming
       replication to reach durable storage.</entry>
     </row>
     <row>
      <entry><literal>TimelineHistoryFileWrite</literal></entry>
      <entry>Waiting for a write of a timeline history file received via
       streaming replication.</entry>
     </row>
     <row>
      <entry><literal>TimelineHistoryRead</literal></entry>
      <entry>Waiting for a read of a timeline history file.</entry>
     </row>
     <row>
      <entry><literal>TimelineHistorySync</literal></entry>
      <entry>Waiting for a newly created timeline history file to reach durable
       storage.</entry>
     </row>
     <row>
      <entry><literal>TimelineHistoryWrite</literal></entry>
      <entry>Waiting for a write of a newly created timeline history
       file.</entry>
     </row>
     <row>
      <entry><literal>TwophaseFileRead</literal></entry>
      <entry>Waiting for a read of a two phase state file.</entry>
     </row>
     <row>
      <entry><literal>TwophaseFileSync</literal></entry>
      <entry>Waiting for a two phase state file to reach durable storage.</entry>
     </row>
     <row>
      <entry><literal>TwophaseFileWrite</literal></entry>
      <entry>Waiting for a write of a two phase state file.</entry>
     </row>
     <row>
      <entry><literal>WALBootstrapSync</literal></entry>
      <entry>Waiting for WAL to reach durable storage during
       bootstrapping.</entry>
     </row>
     <row>
      <entry><literal>WALBootstrapWrite</literal></entry>
      <entry>Waiting for a write of a WAL page during bootstrapping.</entry>
     </row>
     <row>
      <entry><literal>WALCopyRead</literal></entry>
      <entry>Waiting for a read when creating a new WAL segment by copying an
       existing one.</entry>
     </row>
     <row>
      <entry><literal>WALCopySync</literal></entry>
      <entry>Waiting for a new WAL segment created by copying an existing one to
       reach durable storage.</entry>
     </row>
     <row>
      <entry><literal>WALCopyWrite</literal></entry>
      <entry>Waiting for a write when creating a new WAL segment by copying an
       existing one.</entry>
     </row>
     <row>
      <entry><literal>WALInitSync</literal></entry>
      <entry>Waiting for a newly initialized WAL file to reach durable
       storage.</entry>
     </row>
     <row>
      <entry><literal>WALInitWrite</literal></entry>
      <entry>Waiting for a write while initializing a new WAL file.</entry>
     </row>
     <row>
      <entry><literal>WALRead</literal></entry>
      <entry>Waiting for a read from a WAL file.</entry>
     </row>
     <row>
      <entry><literal>WALSenderTimelineHistoryRead</literal></entry>
      <entry>Waiting for a read from a timeline history file during a walsender
       timeline command.</entry>
     </row>
     <row>
      <entry><literal>WALSync</literal></entry>
      <entry>Waiting for a WAL file to reach durable storage.</entry>
     </row>
     <row>
      <entry><literal>WALSyncMethodAssign</literal></entry>
      <entry>Waiting for data to reach durable storage while assigning a new
       WAL sync method.</entry>
     </row>
     <row>
      <entry><literal>WALWrite</literal></entry>
      <entry>Waiting for a write to a WAL file.</entry>
     </row>
     <row>
      <entry><literal>LogicalChangesRead</literal></entry>
      <entry>Waiting for a read from a logical changes file.</entry>
     </row>
     <row>
      <entry><literal>LogicalChangesWrite</literal></entry>
      <entry>Waiting for a write to a logical changes file.</entry>
     </row>
     <row>
      <entry><literal>LogicalSubxactRead</literal></entry>
      <entry>Waiting for a read from a logical subxact file.</entry>
     </row>
     <row>
      <entry><literal>LogicalSubxactWrite</literal></entry>
      <entry>Waiting for a write to a logical subxact file.</entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="wait-event-ipc-table">
   <title>Wait Events of Type <literal>IPC</literal></title>
   <tgroup cols="2">
    <thead>
     <row>
      <entry><literal>IPC</literal> Wait Event</entry>
      <entry>Description</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><literal>BackupWaitWalArchive</literal></entry>
      <entry>Waiting for WAL files required for a backup to be successfully
       archived.</entry>
     </row>
     <row>
      <entry><literal>BgWorkerShutdown</literal></entry>
      <entry>Waiting for background worker to shut down.</entry>
     </row>
     <row>
      <entry><literal>BgWorkerStartup</literal></entry>
      <entry>Waiting for background worker to start up.</entry>
     </row>
     <row>
      <entry><literal>BtreePage</literal></entry>
      <entry>Waiting for the page number needed to continue a parallel B-tree
       scan to become available.</entry>
     </row>
     <row>
      <entry><literal>CheckpointDone</literal></entry>
      <entry>Waiting for a checkpoint to complete.</entry>
     </row>
     <row>
      <entry><literal>CheckpointStart</literal></entry>
      <entry>Waiting for a checkpoint to start.</entry>
     </row>
     <row>
      <entry><literal>ExecuteGather</literal></entry>
      <entry>Waiting for activity from a child process while
       executing a <literal>Gather</literal> plan node.</entry>
     </row>
     <row>
      <entry><literal>HashBatchAllocate</literal></entry>
      <entry>Waiting for an elected Parallel Hash participant to allocate a hash
       table.</entry>
     </row>
     <row>
      <entry><literal>HashBatchElect</literal></entry>
      <entry>Waiting to elect a Parallel Hash participant to allocate a hash
       table.</entry>
     </row>
     <row>
      <entry><literal>HashBatchLoad</literal></entry>
      <entry>Waiting for other Parallel Hash participants to finish loading a
       hash table.</entry>
     </row>
     <row>
      <entry><literal>HashBuildAllocate</literal></entry>
      <entry>Waiting for an elected Parallel Hash participant to allocate the
       initial hash table.</entry>
     </row>
     <row>
      <entry><literal>HashBuildElect</literal></entry>
      <entry>Waiting to elect a Parallel Hash participant to allocate the
       initial hash table.</entry>
     </row>
     <row>
      <entry><literal>HashBuildHashInner</literal></entry>
      <entry>Waiting for other Parallel Hash participants to finish hashing the
       inner relation.</entry>
     </row>
     <row>
      <entry><literal>HashBuildHashOuter</literal></entry>
      <entry>Waiting for other Parallel Hash participants to finish partitioning
       the outer relation.</entry>
     </row>
     <row>
      <entry><literal>HashGrowBatchesAllocate</literal></entry>
      <entry>Waiting for an elected Parallel Hash participant to allocate more
       batches.</entry>
     </row>
     <row>
      <entry><literal>HashGrowBatchesDecide</literal></entry>
      <entry>Waiting to elect a Parallel Hash participant to decide on future
       batch growth.</entry>
     </row>
     <row>
      <entry><literal>HashGrowBatchesElect</literal></entry>
      <entry>Waiting to elect a Parallel Hash participant to allocate more
       batches.</entry>
     </row>
     <row>
      <entry><literal>HashGrowBatchesFinish</literal></entry>
      <entry>Waiting for an elected Parallel Hash participant to decide on
       future batch growth.</entry>
     </row>
     <row>
      <entry><literal>HashGrowBatchesRepartition</literal></entry>
      <entry>Waiting for other Parallel Hash participants to finish
       repartitioning.</entry>
     </row>
     <row>
      <entry><literal>HashGrowBucketsAllocate</literal></entry>
      <entry>Waiting for an elected Parallel Hash participant to finish
       allocating more buckets.</entry>
     </row>
     <row>
      <entry><literal>HashGrowBucketsElect</literal></entry>
      <entry>Waiting to elect a Parallel Hash participant to allocate more
       buckets.</entry>
     </row>
     <row>
      <entry><literal>HashGrowBucketsReinsert</literal></entry>
      <entry>Waiting for other Parallel Hash participants to finish inserting
       tuples into new buckets.</entry>
     </row>
     <row>
      <entry><literal>LogicalSyncData</literal></entry>
      <entry>Waiting for a logical replication remote server to send data for
       initial table synchronization.</entry>
     </row>
     <row>
      <entry><literal>LogicalSyncStateChange</literal></entry>
      <entry>Waiting for a logical replication remote server to change
       state.</entry>
     </row>
     <row>
      <entry><literal>MessageQueueInternal</literal></entry>
      <entry>Waiting for another process to be attached to a shared message
       queue.</entry>
     </row>
     <row>
      <entry><literal>MessageQueuePutMessage</literal></entry>
      <entry>Waiting to write a protocol message to a shared message queue.</entry>
     </row>
     <row>
      <entry><literal>MessageQueueReceive</literal></entry>
      <entry>Waiting to receive bytes from a shared message queue.</entry>
     </row>
     <row>
      <entry><literal>MessageQueueSend</literal></entry>
      <entry>Waiting to send bytes to a shared message queue.</entry>
     </row>
     <row>
      <entry><literal>ParallelBitmapScan</literal></entry>
      <entry>Waiting for parallel bitmap scan to become initialized.</entry>
     </row>
     <row>
      <entry><literal>ParallelCreateIndexScan</literal></entry>
      <entry>Waiting for parallel <command>CREATE INDEX</command> workers to
       finish heap scan.</entry>
     </row>
     <row>
      <entry><literal>ParallelFinish</literal></entry>
      <entry>Waiting for parallel workers to finish computing.</entry>
     </row>
     <row>
      <entry><literal>ProcArrayGroupUpdate</literal></entry>
      <entry>Waiting for the group leader to clear the transaction ID at
       end of a parallel operation.</entry>
     </row>
     <row>
      <entry><literal>ProcSignalBarrier</literal></entry>
      <entry>Waiting for a barrier event to be processed by all
       backends.</entry>
     </row>
     <row>
      <entry><literal>Promote</literal></entry>
      <entry>Waiting for standby promotion.</entry>
     </row>
     <row>
      <entry><literal>RecoveryConflictSnapshot</literal></entry>
      <entry>Waiting for recovery conflict resolution for a vacuum
       cleanup.</entry>
     </row>
     <row>
      <entry><literal>RecoveryConflictTablespace</literal></entry>
      <entry>Waiting for recovery conflict resolution for dropping a
       tablespace.</entry>
     </row>
     <row>
      <entry><literal>RecoveryPause</literal></entry>
      <entry>Waiting for recovery to be resumed.</entry>
     </row>
     <row>
      <entry><literal>ReplicationOriginDrop</literal></entry>
      <entry>Waiting for a replication origin to become inactive so it can be
       dropped.</entry>
     </row>
     <row>
      <entry><literal>ReplicationSlotDrop</literal></entry>
      <entry>Waiting for a replication slot to become inactive so it can be
       dropped.</entry>
     </row>
     <row>
      <entry><literal>SafeSnapshot</literal></entry>
      <entry>Waiting to obtain a valid snapshot for a <literal>READ ONLY
       DEFERRABLE</literal> transaction.</entry>
     </row>
     <row>
      <entry><literal>SyncRep</literal></entry>
      <entry>Waiting for confirmation from a remote server during synchronous
       replication.</entry>
     </row>
     <row>
      <entry><literal>XactGroupUpdate</literal></entry>
      <entry>Waiting for the group leader to update transaction status at
       end of a parallel operation.</entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="wait-event-lock-table">
   <title>Wait Events of Type <literal>Lock</literal></title>
   <tgroup cols="2">
    <thead>
     <row>
      <entry><literal>Lock</literal> Wait Event</entry>
      <entry>Description</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><literal>advisory</literal></entry>
      <entry>Waiting to acquire an advisory user lock.</entry>
     </row>
     <row>
      <entry><literal>extend</literal></entry>
      <entry>Waiting to extend a relation.</entry>
     </row>
     <row>
      <entry><literal>frozenid</literal></entry>
      <entry>Waiting to
       update <structname>pg_database</structname>.<structfield>datfrozenxid</structfield>
       and <structname>pg_database</structname>.<structfield>datminmxid</structfield>.</entry>
     </row>
     <row>
      <entry><literal>object</literal></entry>
      <entry>Waiting to acquire a lock on a non-relation database object.</entry>
     </row>
     <row>
      <entry><literal>page</literal></entry>
      <entry>Waiting to acquire a lock on a page of a relation.</entry>
     </row>
     <row>
      <entry><literal>relation</literal></entry>
      <entry>Waiting to acquire a lock on a relation.</entry>
     </row>
     <row>
      <entry><literal>spectoken</literal></entry>
      <entry>Waiting to acquire a speculative insertion lock.</entry>
     </row>
     <row>
      <entry><literal>transactionid</literal></entry>
      <entry>Waiting for a transaction to finish.</entry>
     </row>
     <row>
      <entry><literal>tuple</literal></entry>
      <entry>Waiting to acquire a lock on a tuple.</entry>
     </row>
     <row>
      <entry><literal>userlock</literal></entry>
      <entry>Waiting to acquire a user lock.</entry>
     </row>
     <row>
      <entry><literal>virtualxid</literal></entry>
      <entry>Waiting to acquire a virtual transaction ID lock.</entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="wait-event-lwlock-table">
   <title>Wait Events of Type <literal>LWLock</literal></title>
   <tgroup cols="2">
    <thead>
     <row>
      <entry><literal>LWLock</literal> Wait Event</entry>
      <entry>Description</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><literal>AddinShmemInit</literal></entry>
      <entry>Waiting to manage an extension's space allocation in shared
       memory.</entry>
     </row>
     <row>
      <entry><literal>AutoFile</literal></entry>
      <entry>Waiting to update the <filename>postgresql.auto.conf</filename>
       file.</entry>
     </row>
     <row>
      <entry><literal>Autovacuum</literal></entry>
      <entry>Waiting to read or update the current state of autovacuum
       workers.</entry>
     </row>
     <row>
      <entry><literal>AutovacuumSchedule</literal></entry>
      <entry>Waiting to ensure that a table selected for autovacuum
       still needs vacuuming.</entry>
     </row>
     <row>
      <entry><literal>BackgroundWorker</literal></entry>
      <entry>Waiting to read or update background worker state.</entry>
     </row>
     <row>
      <entry><literal>BtreeVacuum</literal></entry>
      <entry>Waiting to read or update vacuum-related information for a
       B-tree index.</entry>
     </row>
     <row>
      <entry><literal>BufferContent</literal></entry>
      <entry>Waiting to access a data page in memory.</entry>
     </row>
     <row>
      <entry><literal>BufferIO</literal></entry>
      <entry>Waiting for I/O on a data page.</entry>
     </row>
     <row>
      <entry><literal>BufferMapping</literal></entry>
      <entry>Waiting to associate a data block with a buffer in the buffer
       pool.</entry>
     </row>
     <row>
      <entry><literal>Checkpoint</literal></entry>
      <entry>Waiting to begin a checkpoint.</entry>
     </row>
     <row>
      <entry><literal>CheckpointerComm</literal></entry>
      <entry>Waiting to manage fsync requests.</entry>
     </row>
     <row>
      <entry><literal>CommitTs</literal></entry>
      <entry>Waiting to read or update the last value set for a
       transaction commit timestamp.</entry>
     </row>
     <row>
      <entry><literal>CommitTsBuffer</literal></entry>
      <entry>Waiting for I/O on a commit timestamp SLRU buffer.</entry>
     </row>
     <row>
      <entry><literal>CommitTsSLRU</literal></entry>
      <entry>Waiting to access the commit timestamp SLRU cache.</entry>
     </row>
     <row>
      <entry><literal>ControlFile</literal></entry>
      <entry>Waiting to read or update the <filename>pg_control</filename>
       file or create a new WAL file.</entry>
     </row>
     <row>
      <entry><literal>DynamicSharedMemoryControl</literal></entry>
      <entry>Waiting to read or update dynamic shared memory allocation
       information.</entry>
     </row>
     <row>
      <entry><literal>LockFastPath</literal></entry>
      <entry>Waiting to read or update a process' fast-path lock
       information.</entry>
     </row>
     <row>
      <entry><literal>LockManager</literal></entry>
      <entry>Waiting to read or update information
       about <quote>heavyweight</quote> locks.</entry>
     </row>
     <row>
      <entry><literal>LogicalRepWorker</literal></entry>
      <entry>Waiting to read or update the state of logical replication
       workers.</entry>
     </row>
     <row>
      <entry><literal>MultiXactGen</literal></entry>
      <entry>Waiting to read or update shared multixact state.</entry>
     </row>
     <row>
      <entry><literal>MultiXactMemberBuffer</literal></entry>
      <entry>Waiting for I/O on a multixact member SLRU buffer.</entry>
     </row>
     <row>
      <entry><literal>MultiXactMemberSLRU</literal></entry>
      <entry>Waiting to access the multixact member SLRU cache.</entry>
     </row>
     <row>
      <entry><literal>MultiXactOffsetBuffer</literal></entry>
      <entry>Waiting for I/O on a multixact offset SLRU buffer.</entry>
     </row>
     <row>
      <entry><literal>MultiXactOffsetSLRU</literal></entry>
      <entry>Waiting to access the multixact offset SLRU cache.</entry>
     </row>
     <row>
      <entry><literal>MultiXactTruncation</literal></entry>
      <entry>Waiting to read or truncate multixact information.</entry>
     </row>
     <row>
      <entry><literal>NotifyBuffer</literal></entry>
      <entry>Waiting for I/O on a <command>NOTIFY</command> message SLRU
       buffer.</entry>
     </row>
     <row>
      <entry><literal>NotifyQueue</literal></entry>
      <entry>Waiting to read or update <command>NOTIFY</command> messages.</entry>
     </row>
     <row>
      <entry><literal>NotifyQueueTail</literal></entry>
      <entry>Waiting to update limit on <command>NOTIFY</command> message
       storage.</entry>
     </row>
     <row>
      <entry><literal>NotifySLRU</literal></entry>
      <entry>Waiting to access the <command>NOTIFY</command> message SLRU
       cache.</entry>
     </row>
     <row>
      <entry><literal>OidGen</literal></entry>
      <entry>Waiting to allocate a new OID.</entry>
     </row>
     <row>
      <entry><literal>OldSnapshotTimeMap</literal></entry>
      <entry>Waiting to read or update old snapshot control information.</entry>
     </row>
     <row>
      <entry><literal>ParallelAppend</literal></entry>
      <entry>Waiting to choose the next subplan during Parallel Append plan
       execution.</entry>
     </row>
     <row>
      <entry><literal>ParallelHashJoin</literal></entry>
      <entry>Waiting to synchronize workers during Parallel Hash Join plan
       execution.</entry>
     </row>
     <row>
      <entry><literal>ParallelQueryDSA</literal></entry>
      <entry>Waiting for parallel query dynamic shared memory allocation.</entry>
     </row>
     <row>
      <entry><literal>PerSessionDSA</literal></entry>
      <entry>Waiting for parallel query dynamic shared memory allocation.</entry>
     </row>
     <row>
      <entry><literal>PerSessionRecordType</literal></entry>
      <entry>Waiting to access a parallel query's information about composite
       types.</entry>
     </row>
     <row>
      <entry><literal>PerSessionRecordTypmod</literal></entry>
      <entry>Waiting to access a parallel query's information about type
       modifiers that identify anonymous record types.</entry>
     </row>
     <row>
      <entry><literal>PerXactPredicateList</literal></entry>
      <entry>Waiting to access the list of predicate locks held by the current
       serializable transaction during a parallel query.</entry>
     </row>
     <row>
      <entry><literal>PredicateLockManager</literal></entry>
      <entry>Waiting to access predicate lock information used by
       serializable transactions.</entry>
     </row>
     <row>
      <entry><literal>ProcArray</literal></entry>
      <entry>Waiting to access the shared per-process data structures
       (typically, to get a snapshot or report a session's transaction
       ID).</entry>
     </row>
     <row>
      <entry><literal>RelationMapping</literal></entry>
      <entry>Waiting to read or update
       a <filename>pg_filenode.map</filename> file (used to track the
       filenode assignments of certain system catalogs).</entry>
     </row>
     <row>
      <entry><literal>RelCacheInit</literal></entry>
      <entry>Waiting to read or update a <filename>pg_internal.init</filename>
       relation cache initialization file.</entry>
     </row>
     <row>
      <entry><literal>ReplicationOrigin</literal></entry>
      <entry>Waiting to create, drop or use a replication origin.</entry>
     </row>
     <row>
      <entry><literal>ReplicationOriginState</literal></entry>
      <entry>Waiting to read or update the progress of one replication
       origin.</entry>
     </row>
     <row>
      <entry><literal>ReplicationSlotAllocation</literal></entry>
      <entry>Waiting to allocate or free a replication slot.</entry>
     </row>
     <row>
      <entry><literal>ReplicationSlotControl</literal></entry>
      <entry>Waiting to read or update replication slot state.</entry>
     </row>
     <row>
      <entry><literal>ReplicationSlotIO</literal></entry>
      <entry>Waiting for I/O on a replication slot.</entry>
     </row>
     <row>
      <entry><literal>SerialBuffer</literal></entry>
      <entry>Waiting for I/O on a serializable transaction conflict SLRU
       buffer.</entry>
     </row>
     <row>
      <entry><literal>SerializableFinishedList</literal></entry>
      <entry>Waiting to access the list of finished serializable
       transactions.</entry>
     </row>
     <row>
      <entry><literal>SerializablePredicateList</literal></entry>
      <entry>Waiting to access the list of predicate locks held by
       serializable transactions.</entry>
     </row>
     <row>
      <entry><literal>SerializableXactHash</literal></entry>
      <entry>Waiting to read or update information about serializable
       transactions.</entry>
     </row>
     <row>
      <entry><literal>SerialSLRU</literal></entry>
      <entry>Waiting to access the serializable transaction conflict SLRU
       cache.</entry>
     </row>
     <row>
      <entry><literal>SharedTidBitmap</literal></entry>
      <entry>Waiting to access a shared TID bitmap during a parallel bitmap
       index scan.</entry>
     </row>
     <row>
      <entry><literal>SharedTupleStore</literal></entry>
      <entry>Waiting to access a shared tuple store during parallel
       query.</entry>
     </row>
     <row>
      <entry><literal>ShmemIndex</literal></entry>
      <entry>Waiting to find or allocate space in shared memory.</entry>
     </row>
     <row>
      <entry><literal>SInvalRead</literal></entry>
      <entry>Waiting to retrieve messages from the shared catalog invalidation
       queue.</entry>
     </row>
     <row>
      <entry><literal>SInvalWrite</literal></entry>
      <entry>Waiting to add a message to the shared catalog invalidation
      queue.</entry>
     </row>
     <row>
      <entry><literal>SubtransBuffer</literal></entry>
      <entry>Waiting for I/O on a sub-transaction SLRU buffer.</entry>
     </row>
     <row>
      <entry><literal>SubtransSLRU</literal></entry>
      <entry>Waiting to access the sub-transaction SLRU cache.</entry>
     </row>
     <row>
      <entry><literal>SyncRep</literal></entry>
      <entry>Waiting to read or update information about the state of
       synchronous replication.</entry>
     </row>
     <row>
      <entry><literal>SyncScan</literal></entry>
      <entry>Waiting to select the starting location of a synchronized table
       scan.</entry>
     </row>
     <row>
      <entry><literal>TablespaceCreate</literal></entry>
      <entry>Waiting to create or drop a tablespace.</entry>
     </row>
     <row>
      <entry><literal>TwoPhaseState</literal></entry>
      <entry>Waiting to read or update the state of prepared transactions.</entry>
     </row>
     <row>
      <entry><literal>WALBufMapping</literal></entry>
      <entry>Waiting to replace a page in WAL buffers.</entry>
     </row>
     <row>
      <entry><literal>WALInsert</literal></entry>
      <entry>Waiting to insert WAL data into a memory buffer.</entry>
     </row>
     <row>
      <entry><literal>WALWrite</literal></entry>
      <entry>Waiting for WAL buffers to be written to disk.</entry>
     </row>
     <row>
      <entry><literal>WrapLimitsVacuum</literal></entry>
      <entry>Waiting to update limits on transaction id and multixact
       consumption.</entry>
     </row>
     <row>
      <entry><literal>XactBuffer</literal></entry>
      <entry>Waiting for I/O on a transaction status SLRU buffer.</entry>
     </row>
     <row>
      <entry><literal>XactSLRU</literal></entry>
      <entry>Waiting to access the transaction status SLRU cache.</entry>
     </row>
     <row>
      <entry><literal>XactTruncation</literal></entry>
      <entry>Waiting to execute <function>pg_xact_status</function> or update
       the oldest transaction ID available to it.</entry>
     </row>
     <row>
      <entry><literal>XidGen</literal></entry>
      <entry>Waiting to allocate a new transaction ID.</entry>
     </row>
    </tbody>
   </tgroup>
  </table>

   <note>
    <para>
     Extensions can add <literal>LWLock</literal> types to the list shown in
     <xref linkend="wait-event-lwlock-table"/>.  In some cases, the name
     assigned by an extension will not be available in all server processes;
     so an <literal>LWLock</literal> wait event might be reported as
     just <quote><literal>extension</literal></quote> rather than the
     extension-assigned name.
    </para>
   </note>

  <table id="wait-event-timeout-table">
   <title>Wait Events of Type <literal>Timeout</literal></title>
   <tgroup cols="2">
    <thead>
     <row>
      <entry><literal>Timeout</literal> Wait Event</entry>
      <entry>Description</entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry><literal>BaseBackupThrottle</literal></entry>
      <entry>Waiting during base backup when throttling activity.</entry>
     </row>
     <row>
      <entry><literal>PgSleep</literal></entry>
      <entry>Waiting due to a call to <function>pg_sleep</function> or
       a sibling function.</entry>
     </row>
     <row>
      <entry><literal>RecoveryApplyDelay</literal></entry>
      <entry>Waiting to apply WAL during recovery because of a delay
       setting.</entry>
     </row>
     <row>
      <entry><literal>RecoveryRetrieveRetryInterval</literal></entry>
      <entry>Waiting during recovery when WAL data is not available from any
       source (<filename>pg_wal</filename>, archive or stream).</entry>
     </row>
     <row>
      <entry><literal>VacuumDelay</literal></entry>
      <entry>Waiting in a cost-based vacuum delay point.</entry>
     </row>
    </tbody>
   </tgroup>
  </table>

   <para>
     Here is an example of how wait events can be viewed:

<programlisting>
SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event is NOT NULL;
 pid  | wait_event_type | wait_event 
------+-----------------+------------
 2540 | Lock            | relation
 6644 | LWLock          | ProcArray
(2 rows)
</programlisting>
   </para>

 </sect2>

 <sect2 id="monitoring-pg-stat-replication-view">
  <title><structname>pg_stat_replication</structname></title>

  <indexterm>
   <primary>pg_stat_replication</primary>
  </indexterm>

   <para>
   The <structname>pg_stat_replication</structname> view will contain one row
   per WAL sender process, showing statistics about replication to that
   sender's connected standby server.  Only directly connected standbys are
   listed; no information is available about downstream standby servers.
  </para>

  <table id="pg-stat-replication-view" xreflabel="pg_stat_replication">
   <title><structname>pg_stat_replication</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of a WAL sender process
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usesysid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the user logged into this WAL sender process
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>usename</structfield> <type>name</type>
      </para>
      <para>
       Name of the user logged into this WAL sender process
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>application_name</structfield> <type>text</type>
      </para>
      <para>
       Name of the application that is connected
       to this WAL sender
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>client_addr</structfield> <type>inet</type>
      </para>
      <para>
       IP address of the client connected to this WAL sender.
       If this field is null, it indicates that the client is
       connected via a Unix socket on the server machine.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>client_hostname</structfield> <type>text</type>
      </para>
      <para>
       Host name of the connected client, as reported by a
       reverse DNS lookup of <structfield>client_addr</structfield>. This field will
       only be non-null for IP connections, and only when <xref linkend="guc-log-hostname"/> is enabled.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>client_port</structfield> <type>integer</type>
      </para>
      <para>
       TCP port number that the client is using for communication
       with this WAL sender, or <literal>-1</literal> if a Unix socket is used
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>backend_start</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time when this process was started, i.e., when the
       client connected to this WAL sender
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>backend_xmin</structfield> <type>xid</type>
      </para>
      <para>
       This standby's <literal>xmin</literal> horizon reported
       by <xref linkend="guc-hot-standby-feedback"/>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>state</structfield> <type>text</type>
      </para>
      <para>
       Current WAL sender state.
       Possible values are:
       <itemizedlist>
        <listitem>
         <para>
          <literal>startup</literal>: This WAL sender is starting up.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>catchup</literal>: This WAL sender's connected standby is
          catching up with the primary.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>streaming</literal>: This WAL sender is streaming changes
          after its connected standby server has caught up with the primary.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>backup</literal>: This WAL sender is sending a backup.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>stopping</literal>: This WAL sender is stopping.
         </para>
        </listitem>
       </itemizedlist>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sent_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location sent on this connection
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>write_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location written to disk by this standby
       server
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>flush_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location flushed to disk by this standby
       server
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>replay_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location replayed into the database on this
       standby server
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>write_lag</structfield> <type>interval</type>
      </para>
      <para>
       Time elapsed between flushing recent WAL locally and receiving
       notification that this standby server has written it (but not yet
       flushed it or applied it).  This can be used to gauge the delay that
       <literal>synchronous_commit</literal> level
       <literal>remote_write</literal> incurred while committing if this
       server was configured as a synchronous standby.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>flush_lag</structfield> <type>interval</type>
      </para>
      <para>
       Time elapsed between flushing recent WAL locally and receiving
       notification that this standby server has written and flushed it
       (but not yet applied it).  This can be used to gauge the delay that
       <literal>synchronous_commit</literal> level
       <literal>on</literal> incurred while committing if this
       server was configured as a synchronous standby.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>replay_lag</structfield> <type>interval</type>
      </para>
      <para>
       Time elapsed between flushing recent WAL locally and receiving
       notification that this standby server has written, flushed and
       applied it.  This can be used to gauge the delay that
       <literal>synchronous_commit</literal> level
       <literal>remote_apply</literal> incurred while committing if this
       server was configured as a synchronous standby.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sync_priority</structfield> <type>integer</type>
      </para>
      <para>
       Priority of this standby server for being chosen as the
       synchronous standby in a priority-based synchronous replication.
       This has no effect in a quorum-based synchronous replication.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sync_state</structfield> <type>text</type>
      </para>
      <para>
       Synchronous state of this standby server.
       Possible values are:
       <itemizedlist>
        <listitem>
         <para>
          <literal>async</literal>: This standby server is asynchronous.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>potential</literal>: This standby server is now asynchronous,
          but can potentially become synchronous if one of current
          synchronous ones fails.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>sync</literal>: This standby server is synchronous.
         </para>
        </listitem>
        <listitem>
         <para>
          <literal>quorum</literal>: This standby server is considered as a candidate
          for quorum standbys.
         </para>
        </listitem>
       </itemizedlist>
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>reply_time</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Send time of last reply message received from standby server
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   The lag times reported in the <structname>pg_stat_replication</structname>
   view are measurements of the time taken for recent WAL to be written,
   flushed and replayed and for the sender to know about it.  These times
   represent the commit delay that was (or would have been) introduced by each
   synchronous commit level, if the remote server was configured as a
   synchronous standby.  For an asynchronous standby, the
   <structfield>replay_lag</structfield> column approximates the delay
   before recent transactions became visible to queries.  If the standby
   server has entirely caught up with the sending server and there is no more
   WAL activity, the most recently measured lag times will continue to be
   displayed for a short time and then show NULL.
  </para>

  <para>
   Lag times work automatically for physical replication. Logical decoding
   plugins may optionally emit tracking messages; if they do not, the tracking
   mechanism will simply display NULL lag.
  </para>

  <note>
   <para>
    The reported lag times are not predictions of how long it will take for
    the standby to catch up with the sending server assuming the current
    rate of replay.  Such a system would show similar times while new WAL is
    being generated, but would differ when the sender becomes idle.  In
    particular, when the standby has caught up completely,
    <structname>pg_stat_replication</structname> shows the time taken to
    write, flush and replay the most recent reported WAL location rather than
    zero as some users might expect.  This is consistent with the goal of
    measuring synchronous commit and transaction visibility delays for
    recent write transactions.
    To reduce confusion for users expecting a different model of lag, the
    lag columns revert to NULL after a short time on a fully replayed idle
    system. Monitoring systems should choose whether to represent this
    as missing data, zero or continue to display the last known value.
   </para>
  </note>

 </sect2>

 <sect2 id="monitoring-pg-stat-replication-slots-view">
  <title><structname>pg_stat_replication_slots</structname></title>

  <indexterm>
   <primary>pg_stat_replication_slots</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_replication_slots</structname> view will contain
   one row per logical replication slot, showing statistics about its usage.
  </para>

  <table id="pg-stat-replication-slots-view" xreflabel="pg_stat_replication_slots">
   <title><structname>pg_stat_replication_slots</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
        Column Type
       </para>
       <para>
        Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>slot_name</structfield> <type>text</type>
       </para>
       <para>
        A unique, cluster-wide identifier for the replication slot
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>spill_txns</structfield> <type>bigint</type>
       </para>
       <para>
        Number of transactions spilled to disk after the memory used by
        logical decoding of changes from WAL for this slot exceeds
        <literal>logical_decoding_work_mem</literal>. The counter gets
        incremented both for toplevel transactions and subtransactions.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>spill_count</structfield> <type>bigint</type>
       </para>
       <para>
        Number of times transactions were spilled to disk while decoding changes
        from WAL for this slot. Transactions may get spilled repeatedly, and
        this counter gets incremented on every such invocation.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>spill_bytes</structfield> <type>bigint</type>
       </para>
       <para>
        Amount of decoded transaction data spilled to disk while performing
        decoding of changes from WAL for this slot. This and other spill
        counters can be used to gauge the I/O which occurred during logical
        decoding and allow tuning <literal>logical_decoding_work_mem</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stream_txns</structfield> <type>bigint</type>
       </para>
       <para>
        Number of in-progress transactions streamed to the decoding output plugin
        after the memory used by logical decoding of changes from WAL for this
        slot exceeds <literal>logical_decoding_work_mem</literal>. Streaming only
        works with toplevel transactions (subtransactions can't be streamed
        independently), so the counter does not get incremented for subtransactions.
       </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stream_count</structfield><type>bigint</type>
       </para>
       <para>
        Number of times in-progress transactions were streamed to the decoding
        output plugin while decoding changes from WAL for this slot. Transactions
        may get streamed repeatedly, and this counter gets incremented on every
        such invocation.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stream_bytes</structfield><type>bigint</type>
       </para>
       <para>
        Amount of decoded in-progress transaction data streamed to the decoding
        output plugin while decoding changes from WAL for this slot. This and other
        streaming counters for this slot can be used to gauge the network I/O which
        occurred during logical decoding and allow tuning <literal>logical_decoding_work_mem</literal>.
       </para>
      </entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
       </para>
       <para>
        Time at which these statistics were last reset
       </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-stat-wal-receiver-view">
  <title><structname>pg_stat_wal_receiver</structname></title>

  <indexterm>
   <primary>pg_stat_wal_receiver</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_wal_receiver</structname> view will contain only
   one row, showing statistics about the WAL receiver from that receiver's
   connected server.
  </para>

  <table id="pg-stat-wal-receiver-view" xreflabel="pg_stat_wal_receiver">
   <title><structname>pg_stat_wal_receiver</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of the WAL receiver process
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>status</structfield> <type>text</type>
      </para>
      <para>
       Activity status of the WAL receiver process
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>receive_start_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       First write-ahead log location used when WAL receiver is
       started
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>receive_start_tli</structfield> <type>integer</type>
      </para>
      <para>
       First timeline number used when WAL receiver is started
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>written_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location already received and written to disk,
       but not flushed. This should not be used for data integrity checks.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>flushed_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location already received and flushed to
       disk, the initial value of this field being the first log location used
       when WAL receiver is started
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>received_tli</structfield> <type>integer</type>
      </para>
      <para>
       Timeline number of last write-ahead log location received and
       flushed to disk, the initial value of this field being the timeline
       number of the first log location used when WAL receiver is started
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_msg_send_time</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Send time of last message received from origin WAL sender
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_msg_receipt_time</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Receipt time of last message received from origin WAL sender
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>latest_end_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location reported to origin WAL sender
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>latest_end_time</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time of last write-ahead log location reported to origin WAL sender
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>slot_name</structfield> <type>text</type>
      </para>
      <para>
       Replication slot name used by this WAL receiver
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sender_host</structfield> <type>text</type>
      </para>
      <para>
       Host of the <productname>PostgreSQL</productname> instance
       this WAL receiver is connected to. This can be a host name,
       an IP address, or a directory path if the connection is via
       Unix socket.  (The path case can be distinguished because it
       will always be an absolute path, beginning with <literal>/</literal>.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sender_port</structfield> <type>integer</type>
      </para>
      <para>
       Port number of the <productname>PostgreSQL</productname> instance
       this WAL receiver is connected to.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conninfo</structfield> <type>text</type>
      </para>
      <para>
       Connection string used by this WAL receiver,
       with security-sensitive fields obfuscated.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-stat-subscription">
  <title><structname>pg_stat_subscription</structname></title>

  <indexterm>
   <primary>pg_stat_subscription</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_subscription</structname> view will contain one
   row per subscription for main worker (with null PID if the worker is
   not running), and additional rows for workers handling the initial data
   copy of the subscribed tables.
  </para>

  <table id="pg-stat-subscription" xreflabel="pg_stat_subscription">
   <title><structname>pg_stat_subscription</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>subid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the subscription
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>subname</structfield> <type>name</type>
      </para>
      <para>
       Name of the subscription
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of the subscription worker process
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the relation that the worker is synchronizing; null for the
       main apply worker
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>received_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location received, the initial value of
       this field being 0
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_msg_send_time</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Send time of last message received from origin WAL sender
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_msg_receipt_time</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Receipt time of last message received from origin WAL sender
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>latest_end_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location reported to origin WAL sender
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>latest_end_time</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time of last write-ahead log location reported to origin WAL
       sender
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-stat-ssl-view">
  <title><structname>pg_stat_ssl</structname></title>

  <indexterm>
   <primary>pg_stat_ssl</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_ssl</structname> view will contain one row per
   backend or WAL sender process, showing statistics about SSL usage on
   this connection. It can be joined to <structname>pg_stat_activity</structname>
   or <structname>pg_stat_replication</structname> on the
   <structfield>pid</structfield> column to get more details about the
   connection.
  </para>

  <table id="pg-stat-ssl-view" xreflabel="pg_stat_ssl">
   <title><structname>pg_stat_ssl</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of a backend or WAL sender process
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>ssl</structfield> <type>boolean</type>
      </para>
      <para>
       True if SSL is used on this connection
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>version</structfield> <type>text</type>
      </para>
      <para>
       Version of SSL in use, or NULL if SSL is not in use
       on this connection
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>cipher</structfield> <type>text</type>
      </para>
      <para>
       Name of SSL cipher in use, or NULL if SSL is not in use
       on this connection
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>bits</structfield> <type>integer</type>
      </para>
      <para>
       Number of bits in the encryption algorithm used, or NULL
       if SSL is not used on this connection
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>compression</structfield> <type>boolean</type>
      </para>
      <para>
       True if SSL compression is in use, false if not,
       or NULL if SSL is not in use on this connection
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>client_dn</structfield> <type>text</type>
      </para>
      <para>
       Distinguished Name (DN) field from the client certificate
       used, or NULL if no client certificate was supplied or if SSL
       is not in use on this connection. This field is truncated if the
       DN field is longer than <symbol>NAMEDATALEN</symbol> (64 characters
       in a standard build).
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>client_serial</structfield> <type>numeric</type>
      </para>
      <para>
       Serial number of the client certificate, or NULL if no client
       certificate was supplied or if SSL is not in use on this connection.  The
       combination of certificate serial number and certificate issuer uniquely
       identifies a certificate (unless the issuer erroneously reuses serial
       numbers).
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>issuer_dn</structfield> <type>text</type>
      </para>
      <para>
       DN of the issuer of the client certificate, or NULL if no client
       certificate was supplied or if SSL is not in use on this connection.
       This field is truncated like <structfield>client_dn</structfield>.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-stat-gssapi-view">
  <title><structname>pg_stat_gssapi</structname></title>

  <indexterm>
   <primary>pg_stat_gssapi</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_gssapi</structname> view will contain one row per
   backend, showing information about GSSAPI usage on this connection. It can
   be joined to <structname>pg_stat_activity</structname> or
   <structname>pg_stat_replication</structname> on the
   <structfield>pid</structfield> column to get more details about the
   connection.
  </para>

  <table id="pg-stat-gssapi-view" xreflabel="pg_stat_gssapi">
   <title><structname>pg_stat_gssapi</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of a backend
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>gss_authenticated</structfield> <type>boolean</type>
      </para>
      <para>
       True if GSSAPI authentication was used for this connection
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>principal</structfield> <type>text</type>
      </para>
      <para>
       Principal used to authenticate this connection, or NULL
       if GSSAPI was not used to authenticate this connection.  This
       field is truncated if the principal is longer than
       <symbol>NAMEDATALEN</symbol> (64 characters in a standard build).
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>encrypted</structfield> <type>boolean</type>
      </para>
      <para>
       True if GSSAPI encryption is in use on this connection
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-stat-archiver-view">
  <title><structname>pg_stat_archiver</structname></title>

  <indexterm>
   <primary>pg_stat_archiver</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_archiver</structname> view will always have a
   single row, containing data about the archiver process of the cluster.
  </para>

  <table id="pg-stat-archiver-view" xreflabel="pg_stat_archiver">
   <title><structname>pg_stat_archiver</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>archived_count</structfield> <type>bigint</type>
      </para>
      <para>
       Number of WAL files that have been successfully archived
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_archived_wal</structfield> <type>text</type>
      </para>
      <para>
       Name of the last WAL file successfully archived
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_archived_time</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time of the last successful archive operation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>failed_count</structfield> <type>bigint</type>
      </para>
      <para>
       Number of failed attempts for archiving WAL files
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_failed_wal</structfield> <type>text</type>
      </para>
      <para>
       Name of the WAL file of the last failed archival operation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_failed_time</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time of the last failed archival operation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time at which these statistics were last reset
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-stat-bgwriter-view">
  <title><structname>pg_stat_bgwriter</structname></title>

  <indexterm>
   <primary>pg_stat_bgwriter</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_bgwriter</structname> view will always have a
   single row, containing global data for the cluster.
  </para>

  <table id="pg-stat-bgwriter-view" xreflabel="pg_stat_bgwriter">
   <title><structname>pg_stat_bgwriter</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>checkpoints_timed</structfield> <type>bigint</type>
      </para>
      <para>
       Number of scheduled checkpoints that have been performed
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>checkpoints_req</structfield> <type>bigint</type>
      </para>
      <para>
       Number of requested checkpoints that have been performed
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>checkpoint_write_time</structfield> <type>double precision</type>
      </para>
      <para>
       Total amount of time that has been spent in the portion of
       checkpoint processing where files are written to disk, in milliseconds
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>checkpoint_sync_time</structfield> <type>double precision</type>
      </para>
      <para>
       Total amount of time that has been spent in the portion of
       checkpoint processing where files are synchronized to disk, in
       milliseconds
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>buffers_checkpoint</structfield> <type>bigint</type>
      </para>
      <para>
       Number of buffers written during checkpoints
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>buffers_clean</structfield> <type>bigint</type>
      </para>
      <para>
       Number of buffers written by the background writer
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>maxwritten_clean</structfield> <type>bigint</type>
      </para>
      <para>
       Number of times the background writer stopped a cleaning
       scan because it had written too many buffers
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>buffers_backend</structfield> <type>bigint</type>
      </para>
      <para>
       Number of buffers written directly by a backend
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>buffers_backend_fsync</structfield> <type>bigint</type>
      </para>
      <para>
       Number of times a backend had to execute its own
       <function>fsync</function> call (normally the background writer handles those
       even when the backend does its own write)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>buffers_alloc</structfield> <type>bigint</type>
      </para>
      <para>
       Number of buffers allocated
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time at which these statistics were last reset
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-stat-wal-view">
   <title><structname>pg_stat_wal</structname></title>

  <indexterm>
   <primary>pg_stat_wal</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_wal</structname> view will always have a
   single row, containing data about WAL activity of the cluster.
  </para>

  <table id="pg-stat-wal-view" xreflabel="pg_stat_wal">
   <title><structname>pg_stat_wal</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>wal_records</structfield> <type>bigint</type>
      </para>
      <para>
       Total number of WAL records generated
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>wal_fpi</structfield> <type>bigint</type>
      </para>
      <para>
       Total number of WAL full page images generated
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>wal_bytes</structfield> <type>numeric</type>
      </para>
      <para>
       Total amount of WAL generated in bytes
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>wal_buffers_full</structfield> <type>bigint</type>
      </para>
      <para>
       Number of times WAL data was written to disk because WAL buffers became full
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time at which these statistics were last reset
      </para></entry>
     </row>
     </tbody>
   </tgroup>
  </table>

</sect2>

 <sect2 id="monitoring-pg-stat-database-view">
  <title><structname>pg_stat_database</structname></title>

  <indexterm>
   <primary>pg_stat_database</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_database</structname> view will contain one row
   for each database in the cluster, plus one for shared objects, showing
   database-wide statistics.
  </para>

  <table id="pg-stat-database-view" xreflabel="pg_stat_database">
   <title><structname>pg_stat_database</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datid</structfield> <type>oid</type>
      </para>
      <para>
       OID of this database, or 0 for objects belonging to a shared
       relation
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datname</structfield> <type>name</type>
      </para>
      <para>
       Name of this database, or <literal>NULL</literal> for shared
       objects.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>numbackends</structfield> <type>integer</type>
      </para>
      <para>
       Number of backends currently connected to this database, or
       <literal>NULL</literal> for shared objects.  This is the only column
       in this view that returns a value reflecting current state; all other
       columns return the accumulated values since the last reset.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>xact_commit</structfield> <type>bigint</type>
      </para>
      <para>
       Number of transactions in this database that have been
       committed
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>xact_rollback</structfield> <type>bigint</type>
      </para>
      <para>
       Number of transactions in this database that have been
       rolled back
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>blks_read</structfield> <type>bigint</type>
      </para>
      <para>
       Number of disk blocks read in this database
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>blks_hit</structfield> <type>bigint</type>
      </para>
      <para>
       Number of times disk blocks were found already in the buffer
       cache, so that a read was not necessary (this only includes hits in the
       PostgreSQL buffer cache, not the operating system's file system cache)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tup_returned</structfield> <type>bigint</type>
      </para>
      <para>
       Number of rows returned by queries in this database
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tup_fetched</structfield> <type>bigint</type>
      </para>
      <para>
       Number of rows fetched by queries in this database
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tup_inserted</structfield> <type>bigint</type>
      </para>
      <para>
       Number of rows inserted by queries in this database
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tup_updated</structfield> <type>bigint</type>
      </para>
      <para>
       Number of rows updated by queries in this database
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tup_deleted</structfield> <type>bigint</type>
      </para>
      <para>
       Number of rows deleted by queries in this database
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>conflicts</structfield> <type>bigint</type>
      </para>
      <para>
       Number of queries canceled due to conflicts with recovery
       in this database. (Conflicts occur only on standby servers; see
       <link linkend="monitoring-pg-stat-database-conflicts-view">
       <structname>pg_stat_database_conflicts</structname></link> for details.)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>temp_files</structfield> <type>bigint</type>
      </para>
      <para>
       Number of temporary files created by queries in this database.
       All temporary files are counted, regardless of why the temporary file
       was created (e.g., sorting or hashing), and regardless of the
       <xref linkend="guc-log-temp-files"/> setting.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>temp_bytes</structfield> <type>bigint</type>
      </para>
      <para>
       Total amount of data written to temporary files by queries in
       this database. All temporary files are counted, regardless of why
       the temporary file was created, and
       regardless of the <xref linkend="guc-log-temp-files"/> setting.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>deadlocks</structfield> <type>bigint</type>
      </para>
      <para>
       Number of deadlocks detected in this database
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>checksum_failures</structfield> <type>bigint</type>
      </para>
      <para>
       Number of data page checksum failures detected in this
       database (or on a shared object), or NULL if data checksums are not
       enabled.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>checksum_last_failure</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time at which the last data page checksum failure was detected in
       this database (or on a shared object), or NULL if data checksums are not
       enabled.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>blk_read_time</structfield> <type>double precision</type>
      </para>
      <para>
       Time spent reading data file blocks by backends in this database,
       in milliseconds (if <xref linkend="guc-track-io-timing"/> is enabled,
       otherwise zero)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>blk_write_time</structfield> <type>double precision</type>
      </para>
      <para>
       Time spent writing data file blocks by backends in this database,
       in milliseconds (if <xref linkend="guc-track-io-timing"/> is enabled,
       otherwise zero)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time at which these statistics were last reset
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-stat-database-conflicts-view">
  <title><structname>pg_stat_database_conflicts</structname></title>

  <indexterm>
   <primary>pg_stat_database_conflicts</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_database_conflicts</structname> view will contain
   one row per database, showing database-wide statistics about
   query cancels occurring due to conflicts with recovery on standby servers.
   This view will only contain information on standby servers, since
   conflicts do not occur on primary servers.
  </para>

  <table id="pg-stat-database-conflicts-view" xreflabel="pg_stat_database_conflicts">
   <title><structname>pg_stat_database_conflicts</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datid</structfield> <type>oid</type>
      </para>
      <para>
       OID of a database
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datname</structfield> <type>name</type>
      </para>
      <para>
       Name of this database
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>confl_tablespace</structfield> <type>bigint</type>
      </para>
      <para>
       Number of queries in this database that have been canceled due to
       dropped tablespaces
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>confl_lock</structfield> <type>bigint</type>
      </para>
      <para>
       Number of queries in this database that have been canceled due to
       lock timeouts
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>confl_snapshot</structfield> <type>bigint</type>
      </para>
      <para>
       Number of queries in this database that have been canceled due to
       old snapshots
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>confl_bufferpin</structfield> <type>bigint</type>
      </para>
      <para>
       Number of queries in this database that have been canceled due to
       pinned buffers
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>confl_deadlock</structfield> <type>bigint</type>
      </para>
      <para>
       Number of queries in this database that have been canceled due to
       deadlocks
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-stat-all-tables-view">
  <title><structname>pg_stat_all_tables</structname></title>

  <indexterm>
   <primary>pg_stat_all_tables</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_all_tables</structname> view will contain
   one row for each table in the current database (including TOAST
   tables), showing statistics about accesses to that specific table. The
   <structname>pg_stat_user_tables</structname> and
   <structname>pg_stat_sys_tables</structname> views
   contain the same information,
   but filtered to only show user and system tables respectively.
  </para>

  <table id="pg-stat-all-tables-view" xreflabel="pg_stat_all_tables">
   <title><structname>pg_stat_all_tables</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relid</structfield> <type>oid</type>
      </para>
      <para>
       OID of a table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
      </para>
      <para>
       Name of the schema that this table is in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relname</structfield> <type>name</type>
      </para>
      <para>
       Name of this table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>seq_scan</structfield> <type>bigint</type>
      </para>
      <para>
       Number of sequential scans initiated on this table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>seq_tup_read</structfield> <type>bigint</type>
      </para>
      <para>
       Number of live rows fetched by sequential scans
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>idx_scan</structfield> <type>bigint</type>
      </para>
      <para>
       Number of index scans initiated on this table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>idx_tup_fetch</structfield> <type>bigint</type>
      </para>
      <para>
       Number of live rows fetched by index scans
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>n_tup_ins</structfield> <type>bigint</type>
      </para>
      <para>
       Number of rows inserted
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>n_tup_upd</structfield> <type>bigint</type>
      </para>
      <para>
       Number of rows updated (includes HOT updated rows)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>n_tup_del</structfield> <type>bigint</type>
      </para>
      <para>
       Number of rows deleted
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>n_tup_hot_upd</structfield> <type>bigint</type>
      </para>
      <para>
       Number of rows HOT updated (i.e., with no separate index
       update required)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>n_live_tup</structfield> <type>bigint</type>
      </para>
      <para>
       Estimated number of live rows
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>n_dead_tup</structfield> <type>bigint</type>
      </para>
      <para>
       Estimated number of dead rows
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>n_mod_since_analyze</structfield> <type>bigint</type>
      </para>
      <para>
       Estimated number of rows modified since this table was last analyzed
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>n_ins_since_vacuum</structfield> <type>bigint</type>
      </para>
      <para>
       Estimated number of rows inserted since this table was last vacuumed
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_vacuum</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Last time at which this table was manually vacuumed
       (not counting <command>VACUUM FULL</command>)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_autovacuum</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Last time at which this table was vacuumed by the autovacuum
       daemon
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_analyze</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Last time at which this table was manually analyzed
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_autoanalyze</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Last time at which this table was analyzed by the autovacuum
       daemon
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>vacuum_count</structfield> <type>bigint</type>
      </para>
      <para>
       Number of times this table has been manually vacuumed
       (not counting <command>VACUUM FULL</command>)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>autovacuum_count</structfield> <type>bigint</type>
      </para>
      <para>
       Number of times this table has been vacuumed by the autovacuum
       daemon
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>analyze_count</structfield> <type>bigint</type>
      </para>
      <para>
       Number of times this table has been manually analyzed
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>autoanalyze_count</structfield> <type>bigint</type>
      </para>
      <para>
       Number of times this table has been analyzed by the autovacuum
       daemon
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-stat-all-indexes-view">
  <title><structname>pg_stat_all_indexes</structname></title>

  <indexterm>
   <primary>pg_stat_all_indexes</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_all_indexes</structname> view will contain
   one row for each index in the current database,
   showing statistics about accesses to that specific index. The
   <structname>pg_stat_user_indexes</structname> and
   <structname>pg_stat_sys_indexes</structname> views
   contain the same information,
   but filtered to only show user and system indexes respectively.
  </para>

  <table id="pg-stat-all-indexes-view" xreflabel="pg_stat_all_indexes">
   <title><structname>pg_stat_all_indexes</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the table for this index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indexrelid</structfield> <type>oid</type>
      </para>
      <para>
       OID of this index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
      </para>
      <para>
       Name of the schema this index is in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relname</structfield> <type>name</type>
      </para>
      <para>
       Name of the table for this index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indexrelname</structfield> <type>name</type>
      </para>
      <para>
       Name of this index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>idx_scan</structfield> <type>bigint</type>
      </para>
      <para>
       Number of index scans initiated on this index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>idx_tup_read</structfield> <type>bigint</type>
      </para>
      <para>
       Number of index entries returned by scans on this index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>idx_tup_fetch</structfield> <type>bigint</type>
      </para>
      <para>
       Number of live table rows fetched by simple index scans using this
       index
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   Indexes can be used by simple index scans, <quote>bitmap</quote> index scans,
   and the optimizer.  In a bitmap scan
   the output of several indexes can be combined via AND or OR rules,
   so it is difficult to associate individual heap row fetches
   with specific indexes when a bitmap scan is used.  Therefore, a bitmap
   scan increments the
   <structname>pg_stat_all_indexes</structname>.<structfield>idx_tup_read</structfield>
   count(s) for the index(es) it uses, and it increments the
   <structname>pg_stat_all_tables</structname>.<structfield>idx_tup_fetch</structfield>
   count for the table, but it does not affect
   <structname>pg_stat_all_indexes</structname>.<structfield>idx_tup_fetch</structfield>.
   The optimizer also accesses indexes to check for supplied constants
   whose values are outside the recorded range of the optimizer statistics
   because the optimizer statistics might be stale.
  </para>

  <note>
   <para>
    The <structfield>idx_tup_read</structfield> and <structfield>idx_tup_fetch</structfield> counts
    can be different even without any use of bitmap scans,
    because <structfield>idx_tup_read</structfield> counts
    index entries retrieved from the index while <structfield>idx_tup_fetch</structfield>
    counts live rows fetched from the table.  The latter will be less if any
    dead or not-yet-committed rows are fetched using the index, or if any
    heap fetches are avoided by means of an index-only scan.
   </para>
  </note>

 </sect2>

 <sect2 id="monitoring-pg-statio-all-tables-view">
  <title><structname>pg_statio_all_tables</structname></title>

  <indexterm>
   <primary>pg_statio_all_tables</primary>
  </indexterm>

  <para>
   The <structname>pg_statio_all_tables</structname> view will contain
   one row for each table in the current database (including TOAST
   tables), showing statistics about I/O on that specific table. The
   <structname>pg_statio_user_tables</structname> and
   <structname>pg_statio_sys_tables</structname> views
   contain the same information,
   but filtered to only show user and system tables respectively.
  </para>

  <table id="pg-statio-all-tables-view" xreflabel="pg_statio_all_tables">
   <title><structname>pg_statio_all_tables</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relid</structfield> <type>oid</type>
      </para>
      <para>
       OID of a table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
      </para>
      <para>
       Name of the schema that this table is in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relname</structfield> <type>name</type>
      </para>
      <para>
       Name of this table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>heap_blks_read</structfield> <type>bigint</type>
      </para>
      <para>
       Number of disk blocks read from this table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>heap_blks_hit</structfield> <type>bigint</type>
      </para>
      <para>
       Number of buffer hits in this table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>idx_blks_read</structfield> <type>bigint</type>
      </para>
      <para>
       Number of disk blocks read from all indexes on this table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>idx_blks_hit</structfield> <type>bigint</type>
      </para>
      <para>
       Number of buffer hits in all indexes on this table
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>toast_blks_read</structfield> <type>bigint</type>
      </para>
      <para>
       Number of disk blocks read from this table's TOAST table (if any)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>toast_blks_hit</structfield> <type>bigint</type>
      </para>
      <para>
       Number of buffer hits in this table's TOAST table (if any)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tidx_blks_read</structfield> <type>bigint</type>
      </para>
      <para>
       Number of disk blocks read from this table's TOAST table indexes (if any)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tidx_blks_hit</structfield> <type>bigint</type>
      </para>
      <para>
       Number of buffer hits in this table's TOAST table indexes (if any)
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-statio-all-indexes-view">
  <title><structname>pg_statio_all_indexes</structname></title>

  <indexterm>
   <primary>pg_statio_all_indexes</primary>
  </indexterm>

  <para>
   The <structname>pg_statio_all_indexes</structname> view will contain
   one row for each index in the current database,
   showing statistics about I/O on that specific index. The
   <structname>pg_statio_user_indexes</structname> and
   <structname>pg_statio_sys_indexes</structname> views
   contain the same information,
   but filtered to only show user and system indexes respectively.
  </para>

  <table id="pg-statio-all-indexes-view" xreflabel="pg_statio_all_indexes">
   <title><structname>pg_statio_all_indexes</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the table for this index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indexrelid</structfield> <type>oid</type>
      </para>
      <para>
       OID of this index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
      </para>
      <para>
       Name of the schema this index is in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relname</structfield> <type>name</type>
      </para>
      <para>
       Name of the table for this index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>indexrelname</structfield> <type>name</type>
      </para>
      <para>
       Name of this index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>idx_blks_read</structfield> <type>bigint</type>
      </para>
      <para>
       Number of disk blocks read from this index
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>idx_blks_hit</structfield> <type>bigint</type>
      </para>
      <para>
       Number of buffer hits in this index
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-statio-all-sequences-view">
  <title><structname>pg_statio_all_sequences</structname></title>

  <indexterm>
   <primary>pg_statio_all_sequences</primary>
  </indexterm>

  <para>
   The <structname>pg_statio_all_sequences</structname> view will contain
   one row for each sequence in the current database,
   showing statistics about I/O on that specific sequence.
  </para>

  <table id="pg-statio-all-sequences-view" xreflabel="pg_statio_all_sequences">
   <title><structname>pg_statio_all_sequences</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relid</structfield> <type>oid</type>
      </para>
      <para>
       OID of a sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
      </para>
      <para>
       Name of the schema this sequence is in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relname</structfield> <type>name</type>
      </para>
      <para>
       Name of this sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>blks_read</structfield> <type>bigint</type>
      </para>
      <para>
       Number of disk blocks read from this sequence
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>blks_hit</structfield> <type>bigint</type>
      </para>
      <para>
       Number of buffer hits in this sequence
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-stat-user-functions-view">
  <title><structname>pg_stat_user_functions</structname></title>

  <indexterm>
   <primary>pg_stat_user_functions</primary>
  </indexterm>

  <para>
   The <structname>pg_stat_user_functions</structname> view will contain
   one row for each tracked function, showing statistics about executions of
   that function.  The <xref linkend="guc-track-functions"/> parameter
   controls exactly which functions are tracked.
  </para>

  <table id="pg-stat-user-functions-view" xreflabel="pg_stat_user_functions">
   <title><structname>pg_stat_user_functions</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>funcid</structfield> <type>oid</type>
      </para>
      <para>
       OID of a function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>schemaname</structfield> <type>name</type>
      </para>
      <para>
       Name of the schema this function is in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>funcname</structfield> <type>name</type>
      </para>
      <para>
       Name of this function
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>calls</structfield> <type>bigint</type>
      </para>
      <para>
       Number of times this function has been called
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>total_time</structfield> <type>double precision</type>
      </para>
      <para>
       Total time spent in this function and all other functions
       called by it, in milliseconds
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>self_time</structfield> <type>double precision</type>
      </para>
      <para>
       Total time spent in this function itself, not including
       other functions called by it, in milliseconds
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-stat-slru-view">
  <title><structname>pg_stat_slru</structname></title>

  <indexterm>
   <primary>SLRU</primary>
  </indexterm>

  <indexterm>
   <primary>pg_stat_slru</primary>
  </indexterm>

  <para>
   <productname>PostgreSQL</productname> accesses certain on-disk information
   via <firstterm>SLRU</firstterm> (simple least-recently-used) caches.
   The <structname>pg_stat_slru</structname> view will contain
   one row for each tracked SLRU cache, showing statistics about access
   to cached pages.
  </para>

  <table id="pg-stat-slru-view" xreflabel="pg_stat_slru">
   <title><structname>pg_stat_slru</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>name</structfield> <type>text</type>
      </para>
      <para>
       Name of the SLRU
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>blks_zeroed</structfield> <type>bigint</type>
      </para>
      <para>
       Number of blocks zeroed during initializations
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>blks_hit</structfield> <type>bigint</type>
      </para>
      <para>
       Number of times disk blocks were found already in the SLRU,
       so that a read was not necessary (this only includes hits in the
       SLRU, not the operating system's file system cache)
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>blks_read</structfield> <type>bigint</type>
      </para>
      <para>
       Number of disk blocks read for this SLRU
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>blks_written</structfield> <type>bigint</type>
      </para>
      <para>
       Number of disk blocks written for this SLRU
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>blks_exists</structfield> <type>bigint</type>
      </para>
      <para>
       Number of blocks checked for existence for this SLRU
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>flushes</structfield> <type>bigint</type>
      </para>
      <para>
       Number of flushes of dirty data for this SLRU
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>truncates</structfield> <type>bigint</type>
      </para>
      <para>
       Number of truncates for this SLRU
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Time at which these statistics were last reset
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-stats-functions">
  <title>Statistics Functions</title>

  <para>
   Other ways of looking at the statistics can be set up by writing
   queries that use the same underlying statistics access functions used by
   the standard views shown above.  For details such as the functions' names,
   consult the definitions of the standard views.  (For example, in
   <application>psql</application> you could issue <literal>\d+ pg_stat_activity</literal>.)
   The access functions for per-database statistics take a database OID as an
   argument to identify which database to report on.
   The per-table and per-index functions take a table or index OID.
   The functions for per-function statistics take a function OID.
   Note that only tables, indexes, and functions in the current database
   can be seen with these functions.
  </para>

  <para>
   Additional functions related to statistics collection are listed in <xref
   linkend="monitoring-stats-funcs-table"/>.
  </para>

   <table id="monitoring-stats-funcs-table">
    <title>Additional Statistics Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <!-- See also the entry for this in func.sgml -->
       <entry role="func_table_entry"><para role="func_signature">
        <function>pg_backend_pid</function> ()
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns the process ID of the server process attached to the current
        session.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_activity</primary>
        </indexterm>
        <function>pg_stat_get_activity</function> ( <type>integer</type> )
        <returnvalue>setof record</returnvalue>
       </para>
       <para>
        Returns a record of information about the backend with the specified
        process ID, or one record for each active backend in the system
        if <literal>NULL</literal> is specified.  The fields returned are a
        subset of those in the <structname>pg_stat_activity</structname> view.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_snapshot_timestamp</primary>
        </indexterm>
        <function>pg_stat_get_snapshot_timestamp</function> ()
        <returnvalue>timestamp with time zone</returnvalue>
       </para>
       <para>
        Returns the timestamp of the current statistics snapshot.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_clear_snapshot</primary>
        </indexterm>
        <function>pg_stat_clear_snapshot</function> ()
        <returnvalue>void</returnvalue>
       </para>
       <para>
        Discards the current statistics snapshot.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_reset</primary>
        </indexterm>
        <function>pg_stat_reset</function> ()
        <returnvalue>void</returnvalue>
       </para>
       <para>
        Resets all statistics counters for the current database to zero.
       </para>
       <para>
        This function is restricted to superusers by default, but other users
        can be granted EXECUTE to run the function.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_reset_shared</primary>
        </indexterm>
        <function>pg_stat_reset_shared</function> ( <type>text</type> )
        <returnvalue>void</returnvalue>
       </para>
       <para>
        Resets some cluster-wide statistics counters to zero, depending on the
        argument.  The argument can be <literal>bgwriter</literal> to reset
        all the counters shown in
        the <structname>pg_stat_bgwriter</structname>
        view, <literal>archiver</literal> to reset all the counters shown in
        the <structname>pg_stat_archiver</structname> view or <literal>wal</literal>
        to reset all the counters shown in the <structname>pg_stat_wal</structname> view.
       </para>
       <para>
        This function is restricted to superusers by default, but other users
        can be granted EXECUTE to run the function.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_reset_single_table_counters</primary>
        </indexterm>
        <function>pg_stat_reset_single_table_counters</function> ( <type>oid</type> )
        <returnvalue>void</returnvalue>
       </para>
       <para>
        Resets statistics for a single table or index in the current database
        to zero.
       </para>
       <para>
        This function is restricted to superusers by default, but other users
        can be granted EXECUTE to run the function.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_reset_single_function_counters</primary>
        </indexterm>
        <function>pg_stat_reset_single_function_counters</function> ( <type>oid</type> )
        <returnvalue>void</returnvalue>
       </para>
       <para>
        Resets statistics for a single function in the current database to
        zero.
       </para>
       <para>
        This function is restricted to superusers by default, but other users
        can be granted EXECUTE to run the function.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_reset_slru</primary>
        </indexterm>
        <function>pg_stat_reset_slru</function> ( <type>text</type> )
        <returnvalue>void</returnvalue>
       </para>
       <para>
        Resets statistics to zero for a single SLRU cache, or for all SLRUs in
        the cluster.  If the argument is NULL, all counters shown in
        the <structname>pg_stat_slru</structname> view for all SLRU caches are
        reset.  The argument can be one of
        <literal>CommitTs</literal>,
        <literal>MultiXactMember</literal>,
        <literal>MultiXactOffset</literal>,
        <literal>Notify</literal>,
        <literal>Serial</literal>,
        <literal>Subtrans</literal>, or
        <literal>Xact</literal>
        to reset the counters for only that entry.
        If the argument is <literal>other</literal> (or indeed, any
        unrecognized name), then the counters for all other SLRU caches, such
        as extension-defined caches, are reset.
       </para>
       <para>
        This function is restricted to superusers by default, but other users
        can be granted EXECUTE to run the function.
       </para></entry>
      </row>

      <row>
        <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
          <primary>pg_stat_reset_replication_slot</primary>
        </indexterm>
        <function>pg_stat_reset_replication_slot</function> ( <type>text</type> )
        <returnvalue>void</returnvalue>
       </para>
       <para>
         Resets statistics to zero for a single replication slot, or for all
         replication slots in the cluster.  The argument can be either the name
         of the slot to reset the stats or NULL.  If the argument is NULL, all
         counters shown in the <structname>pg_stat_replication_slots</structname>
         view for all replication slots are reset.
       </para>
       <para>
         This function is restricted to superusers by default, but other users
         can be granted EXECUTE to run the function.
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

  <para>
   <function>pg_stat_get_activity</function>, the underlying function of
   the <structname>pg_stat_activity</structname> view, returns a set of records
   containing all the available information about each backend process.
   Sometimes it may be more convenient to obtain just a subset of this
   information.  In such cases, an older set of per-backend statistics
   access functions can be used; these are shown in <xref
   linkend="monitoring-stats-backend-funcs-table"/>.
   These access functions use a backend ID number, which ranges from one
   to the number of currently active backends.
   The function <function>pg_stat_get_backend_idset</function> provides a
   convenient way to generate one row for each active backend for
   invoking these functions.  For example, to show the <acronym>PID</acronym>s and
   current queries of all backends:

<programlisting>
SELECT pg_stat_get_backend_pid(s.backendid) AS pid,
       pg_stat_get_backend_activity(s.backendid) AS query
    FROM (SELECT pg_stat_get_backend_idset() AS backendid) AS s;
</programlisting>
  </para>

   <table id="monitoring-stats-backend-funcs-table">
    <title>Per-Backend Statistics Functions</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_backend_idset</primary>
        </indexterm>
        <function>pg_stat_get_backend_idset</function> ()
        <returnvalue>setof integer</returnvalue>
       </para>
       <para>
        Returns the set of currently active backend ID numbers (from 1 to the
        number of active backends).
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_backend_activity</primary>
        </indexterm>
        <function>pg_stat_get_backend_activity</function> ( <type>integer</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the text of this backend's most recent query.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_backend_activity_start</primary>
        </indexterm>
        <function>pg_stat_get_backend_activity_start</function> ( <type>integer</type> )
        <returnvalue>timestamp with time zone</returnvalue>
       </para>
       <para>
        Returns the time when the backend's most recent query was started.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_backend_client_addr</primary>
        </indexterm>
        <function>pg_stat_get_backend_client_addr</function> ( <type>integer</type> )
        <returnvalue>inet</returnvalue>
       </para>
       <para>
        Returns the IP address of the client connected to this backend.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_backend_client_port</primary>
        </indexterm>
        <function>pg_stat_get_backend_client_port</function> ( <type>integer</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns the TCP port number that the client is using for communication.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_backend_dbid</primary>
        </indexterm>
        <function>pg_stat_get_backend_dbid</function> ( <type>integer</type> )
        <returnvalue>oid</returnvalue>
       </para>
       <para>
        Returns the OID of the database this backend is connected to.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_backend_pid</primary>
        </indexterm>
        <function>pg_stat_get_backend_pid</function> ( <type>integer</type> )
        <returnvalue>integer</returnvalue>
       </para>
       <para>
        Returns the process ID of this backend.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_backend_start</primary>
        </indexterm>
        <function>pg_stat_get_backend_start</function> ( <type>integer</type> )
        <returnvalue>timestamp with time zone</returnvalue>
       </para>
       <para>
        Returns the time when this process was started.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_backend_userid</primary>
        </indexterm>
        <function>pg_stat_get_backend_userid</function> ( <type>integer</type> )
        <returnvalue>oid</returnvalue>
       </para>
       <para>
        Returns the OID of the user logged into this backend.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_backend_wait_event_type</primary>
        </indexterm>
        <function>pg_stat_get_backend_wait_event_type</function> ( <type>integer</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the wait event type name if this backend is currently waiting,
        otherwise NULL.  See <xref linkend="wait-event-table"/> for details.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_backend_wait_event</primary>
        </indexterm>
        <function>pg_stat_get_backend_wait_event</function> ( <type>integer</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Returns the wait event name if this backend is currently waiting,
        otherwise NULL. See <xref linkend="wait-event-activity-table"/> through
        <xref linkend="wait-event-timeout-table"/>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm>
         <primary>pg_stat_get_backend_xact_start</primary>
        </indexterm>
        <function>pg_stat_get_backend_xact_start</function> ( <type>integer</type> )
        <returnvalue>timestamp with time zone</returnvalue>
       </para>
       <para>
        Returns the time when the backend's current transaction was started.
       </para></entry>
      </row>
     </tbody>
    </tgroup>
   </table>

 </sect2>
 </sect1>

 <sect1 id="monitoring-locks">
  <title>Viewing Locks</title>

  <indexterm zone="monitoring-locks">
   <primary>lock</primary>
   <secondary>monitoring</secondary>
  </indexterm>

  <para>
   Another useful tool for monitoring database activity is the
   <structname>pg_locks</structname> system table.  It allows the
   database administrator to view information about the outstanding
   locks in the lock manager. For example, this capability can be used
   to:

   <itemizedlist>
    <listitem>
     <para>
      View all the locks currently outstanding, all the locks on
      relations in a particular database, all the locks on a
      particular relation, or all the locks held by a particular
      <productname>PostgreSQL</productname> session.
     </para>
    </listitem>

    <listitem>
     <para>
      Determine the relation in the current database with the most
      ungranted locks (which might be a source of contention among
      database clients).
     </para>
    </listitem>

    <listitem>
     <para>
      Determine the effect of lock contention on overall database
      performance, as well as the extent to which contention varies
      with overall database traffic.
     </para>
    </listitem>
   </itemizedlist>

   Details of the <structname>pg_locks</structname> view appear in
   <xref linkend="view-pg-locks"/>.
   For more information on locking and managing concurrency with
   <productname>PostgreSQL</productname>, refer to <xref linkend="mvcc"/>.
  </para>
 </sect1>

 <sect1 id="progress-reporting">
  <title>Progress Reporting</title>

  <para>
   <productname>PostgreSQL</productname> has the ability to report the progress of
   certain commands during command execution.  Currently, the only commands
   which support progress reporting are <command>ANALYZE</command>,
   <command>CLUSTER</command>,
   <command>CREATE INDEX</command>, <command>VACUUM</command>,
   and <xref linkend="protocol-replication-base-backup"/> (i.e., replication
   command that <xref linkend="app-pgbasebackup"/> issues to take
   a base backup).
   This may be expanded in the future.
  </para>

 <sect2 id="analyze-progress-reporting">
  <title>ANALYZE Progress Reporting</title>

  <indexterm>
   <primary>pg_stat_progress_analyze</primary>
  </indexterm>

  <para>
   Whenever <command>ANALYZE</command> is running, the
   <structname>pg_stat_progress_analyze</structname> view will contain a
   row for each backend that is currently running that command.  The tables
   below describe the information that will be reported and provide
   information about how to interpret it.
  </para>

  <table id="pg-stat-progress-analyze-view" xreflabel="pg_stat_progress_analyze">
   <title><structname>pg_stat_progress_analyze</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of backend.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the database to which this backend is connected.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datname</structfield> <type>name</type>
      </para>
      <para>
       Name of the database to which this backend is connected.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the table being analyzed.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>phase</structfield> <type>text</type>
      </para>
      <para>
       Current processing phase. See <xref linkend="analyze-phases"/>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sample_blks_total</structfield> <type>bigint</type>
      </para>
      <para>
       Total number of heap blocks that will be sampled.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>sample_blks_scanned</structfield> <type>bigint</type>
      </para>
      <para>
       Number of heap blocks scanned.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>ext_stats_total</structfield> <type>bigint</type>
      </para>
      <para>
       Number of extended statistics.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>ext_stats_computed</structfield> <type>bigint</type>
      </para>
      <para>
       Number of extended statistics computed. This counter only advances
       when the phase is <literal>computing extended statistics</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>child_tables_total</structfield> <type>bigint</type>
      </para>
      <para>
       Number of child tables.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>child_tables_done</structfield> <type>bigint</type>
      </para>
      <para>
       Number of child tables scanned. This counter only advances when the
       phase is <literal>acquiring inherited sample rows</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>current_child_table_relid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the child table currently being scanned. This field is
       only valid when the phase is
       <literal>acquiring inherited sample rows</literal>.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="analyze-phases">
   <title>ANALYZE phases</title>
   <tgroup cols="2">
    <colspec colname="col1" colwidth="1*"/>
    <colspec colname="col2" colwidth="2*"/>
    <thead>
     <row>
      <entry>Phase</entry>
      <entry>Description</entry>
     </row>
    </thead>
    <tbody>
     <row>
      <entry><literal>initializing</literal></entry>
      <entry>
       The command is preparing to begin scanning the heap.  This phase is
       expected to be very brief.
      </entry>
     </row>
     <row>
      <entry><literal>acquiring sample rows</literal></entry>
      <entry>
       The command is currently scanning the table given by
       <structfield>relid</structfield> to obtain sample rows.
      </entry>
     </row>
     <row>
      <entry><literal>acquiring inherited sample rows</literal></entry>
      <entry>
       The command is currently scanning child tables to obtain sample rows.
       Columns <structfield>child_tables_total</structfield>,
       <structfield>child_tables_done</structfield>, and
       <structfield>current_child_table_relid</structfield> contain the
       progress information for this phase.
      </entry>
     </row>
     <row>
      <entry><literal>computing statistics</literal></entry>
      <entry>
       The command is computing statistics from the sample rows obtained
       during the table scan.
      </entry>
     </row>
     <row>
      <entry><literal>computing extended statistics</literal></entry>
      <entry>
       The command is computing extended statistics from the sample rows
       obtained during the table scan.
      </entry>
     </row>
     <row>
      <entry><literal>finalizing analyze</literal></entry>
      <entry>
       The command is updating <structname>pg_class</structname>. When this
       phase is completed, <command>ANALYZE</command> will end.
      </entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <note>
   <para>
    Note that when <command>ANALYZE</command> is run on a partitioned table,
    all of its partitions are also recursively analyzed.
    In that case, <command>ANALYZE</command>
    progress is reported first for the parent table, whereby its inheritance
    statistics are collected, followed by that for each partition.
   </para>
  </note>
 </sect2>

 <sect2 id="create-index-progress-reporting">
  <title>CREATE INDEX Progress Reporting</title>

  <indexterm>
   <primary>pg_stat_progress_create_index</primary>
  </indexterm>

  <para>
   Whenever <command>CREATE INDEX</command> or <command>REINDEX</command> is running, the
   <structname>pg_stat_progress_create_index</structname> view will contain
   one row for each backend that is currently creating indexes.  The tables
   below describe the information that will be reported and provide information
   about how to interpret it.
  </para>

  <table id="pg-stat-progress-create-index-view" xreflabel="pg_stat_progress_create_index">
   <title><structname>pg_stat_progress_create_index</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of backend.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the database to which this backend is connected.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datname</structfield> <type>name</type>
      </para>
      <para>
       Name of the database to which this backend is connected.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the table on which the index is being created.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>index_relid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the index being created or reindexed.  During a
       non-concurrent <command>CREATE INDEX</command>, this is 0.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>command</structfield> <type>text</type>
      </para>
      <para>
       The command that is running: <literal>CREATE INDEX</literal>,
       <literal>CREATE INDEX CONCURRENTLY</literal>,
       <literal>REINDEX</literal>, or <literal>REINDEX CONCURRENTLY</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>phase</structfield> <type>text</type>
      </para>
      <para>
       Current processing phase of index creation.  See <xref linkend="create-index-phases"/>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>lockers_total</structfield> <type>bigint</type>
      </para>
      <para>
       Total number of lockers to wait for, when applicable.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>lockers_done</structfield> <type>bigint</type>
      </para>
      <para>
       Number of lockers already waited for.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>current_locker_pid</structfield> <type>bigint</type>
      </para>
      <para>
       Process ID of the locker currently being waited for.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>blocks_total</structfield> <type>bigint</type>
      </para>
      <para>
       Total number of blocks to be processed in the current phase.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>blocks_done</structfield> <type>bigint</type>
      </para>
      <para>
       Number of blocks already processed in the current phase.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tuples_total</structfield> <type>bigint</type>
      </para>
      <para>
       Total number of tuples to be processed in the current phase.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tuples_done</structfield> <type>bigint</type>
      </para>
      <para>
       Number of tuples already processed in the current phase.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>partitions_total</structfield> <type>bigint</type>
      </para>
      <para>
       When creating an index on a partitioned table, this column is set to
       the total number of partitions on which the index is to be created.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>partitions_done</structfield> <type>bigint</type>
      </para>
      <para>
       When creating an index on a partitioned table, this column is set to
       the number of partitions on which the index has been completed.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="create-index-phases">
   <title>CREATE INDEX Phases</title>
   <tgroup cols="2">
    <colspec colname="col1" colwidth="1*"/>
    <colspec colname="col2" colwidth="2*"/>
    <thead>
     <row>
      <entry>Phase</entry>
      <entry>Description</entry>
     </row>
    </thead>
    <tbody>
     <row>
      <entry><literal>initializing</literal></entry>
      <entry>
       <command>CREATE INDEX</command> or <command>REINDEX</command> is preparing to create the index.  This
       phase is expected to be very brief.
      </entry>
     </row>
     <row>
      <entry><literal>waiting for writers before build</literal></entry>
      <entry>
       <command>CREATE INDEX CONCURRENTLY</command> or <command>REINDEX CONCURRENTLY</command> is waiting for transactions
       with write locks that can potentially see the table to finish.
       This phase is skipped when not in concurrent mode.
       Columns <structname>lockers_total</structname>, <structname>lockers_done</structname>
       and <structname>current_locker_pid</structname> contain the progress
       information for this phase.
      </entry>
     </row>
     <row>
      <entry><literal>building index</literal></entry>
      <entry>
       The index is being built by the access method-specific code.  In this phase,
       access methods that support progress reporting fill in their own progress data,
       and the subphase is indicated in this column.  Typically,
       <structname>blocks_total</structname> and <structname>blocks_done</structname>
       will contain progress data, as well as potentially
       <structname>tuples_total</structname> and <structname>tuples_done</structname>.
      </entry>
     </row>
     <row>
      <entry><literal>waiting for writers before validation</literal></entry>
      <entry>
       <command>CREATE INDEX CONCURRENTLY</command> or <command>REINDEX CONCURRENTLY</command> is waiting for transactions
       with write locks that can potentially write into the table to finish.
       This phase is skipped when not in concurrent mode.
       Columns <structname>lockers_total</structname>, <structname>lockers_done</structname>
       and <structname>current_locker_pid</structname> contain the progress
       information for this phase.
      </entry>
     </row>
     <row>
      <entry><literal>index validation: scanning index</literal></entry>
      <entry>
       <command>CREATE INDEX CONCURRENTLY</command> is scanning the index searching
       for tuples that need to be validated.
       This phase is skipped when not in concurrent mode.
       Columns <structname>blocks_total</structname> (set to the total size of the index)
       and <structname>blocks_done</structname> contain the progress information for this phase.
      </entry>
     </row>
     <row>
      <entry><literal>index validation: sorting tuples</literal></entry>
      <entry>
       <command>CREATE INDEX CONCURRENTLY</command> is sorting the output of the
       index scanning phase.
      </entry>
     </row>
     <row>
      <entry><literal>index validation: scanning table</literal></entry>
      <entry>
       <command>CREATE INDEX CONCURRENTLY</command> is scanning the table
       to validate the index tuples collected in the previous two phases.
       This phase is skipped when not in concurrent mode.
       Columns <structname>blocks_total</structname> (set to the total size of the table)
       and <structname>blocks_done</structname> contain the progress information for this phase.
      </entry>
     </row>
     <row>
      <entry><literal>waiting for old snapshots</literal></entry>
      <entry>
       <command>CREATE INDEX CONCURRENTLY</command> or <command>REINDEX CONCURRENTLY</command> is waiting for transactions
       that can potentially see the table to release their snapshots.  This
       phase is skipped when not in concurrent mode.
       Columns <structname>lockers_total</structname>, <structname>lockers_done</structname>
       and <structname>current_locker_pid</structname> contain the progress
       information for this phase.
      </entry>
     </row>
     <row>
      <entry><literal>waiting for readers before marking dead</literal></entry>
      <entry>
       <command>REINDEX CONCURRENTLY</command> is waiting for transactions
       with read locks on the table to finish, before marking the old index dead.
       This phase is skipped when not in concurrent mode.
       Columns <structname>lockers_total</structname>, <structname>lockers_done</structname>
       and <structname>current_locker_pid</structname> contain the progress
       information for this phase.
      </entry>
     </row>
     <row>
      <entry><literal>waiting for readers before dropping</literal></entry>
      <entry>
       <command>REINDEX CONCURRENTLY</command> is waiting for transactions
       with read locks on the table to finish, before dropping the old index.
       This phase is skipped when not in concurrent mode.
       Columns <structname>lockers_total</structname>, <structname>lockers_done</structname>
       and <structname>current_locker_pid</structname> contain the progress
       information for this phase.
      </entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="vacuum-progress-reporting">
  <title>VACUUM Progress Reporting</title>

  <indexterm>
   <primary>pg_stat_progress_vacuum</primary>
  </indexterm>

  <para>
   Whenever <command>VACUUM</command> is running, the
   <structname>pg_stat_progress_vacuum</structname> view will contain
   one row for each backend (including autovacuum worker processes) that is
   currently vacuuming.  The tables below describe the information
   that will be reported and provide information about how to interpret it.
   Progress for <command>VACUUM FULL</command> commands is reported via
   <structname>pg_stat_progress_cluster</structname>
   because both <command>VACUUM FULL</command> and <command>CLUSTER</command>
   rewrite the table, while regular <command>VACUUM</command> only modifies it
   in place. See <xref linkend='cluster-progress-reporting'/>.
  </para>

  <table id="pg-stat-progress-vacuum-view" xreflabel="pg_stat_progress_vacuum">
   <title><structname>pg_stat_progress_vacuum</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of backend.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the database to which this backend is connected.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datname</structfield> <type>name</type>
      </para>
      <para>
       Name of the database to which this backend is connected.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the table being vacuumed.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>phase</structfield> <type>text</type>
      </para>
      <para>
       Current processing phase of vacuum.  See <xref linkend="vacuum-phases"/>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>heap_blks_total</structfield> <type>bigint</type>
      </para>
      <para>
       Total number of heap blocks in the table.  This number is reported
       as of the beginning of the scan; blocks added later will not be (and
       need not be) visited by this <command>VACUUM</command>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>heap_blks_scanned</structfield> <type>bigint</type>
      </para>
      <para>
       Number of heap blocks scanned.  Because the
       <link linkend="storage-vm">visibility map</link> is used to optimize scans,
       some blocks will be skipped without inspection; skipped blocks are
       included in this total, so that this number will eventually become
       equal to <structfield>heap_blks_total</structfield> when the vacuum is complete.
       This counter only advances when the phase is <literal>scanning heap</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>heap_blks_vacuumed</structfield> <type>bigint</type>
      </para>
      <para>
       Number of heap blocks vacuumed.  Unless the table has no indexes, this
       counter only advances when the phase is <literal>vacuuming heap</literal>.
       Blocks that contain no dead tuples are skipped, so the counter may
       sometimes skip forward in large increments.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>index_vacuum_count</structfield> <type>bigint</type>
      </para>
      <para>
       Number of completed index vacuum cycles.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>max_dead_tuples</structfield> <type>bigint</type>
      </para>
      <para>
       Number of dead tuples that we can store before needing to perform
       an index vacuum cycle, based on
       <xref linkend="guc-maintenance-work-mem"/>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>num_dead_tuples</structfield> <type>bigint</type>
      </para>
      <para>
       Number of dead tuples collected since the last index vacuum cycle.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="vacuum-phases">
   <title>VACUUM Phases</title>
   <tgroup cols="2">
    <colspec colname="col1" colwidth="1*"/>
    <colspec colname="col2" colwidth="2*"/>
    <thead>
    <row>
      <entry>Phase</entry>
      <entry>Description</entry>
     </row>
    </thead>

   <tbody>
    <row>
     <entry><literal>initializing</literal></entry>
     <entry>
       <command>VACUUM</command> is preparing to begin scanning the heap.  This
       phase is expected to be very brief.
     </entry>
    </row>
    <row>
     <entry><literal>scanning heap</literal></entry>
     <entry>
       <command>VACUUM</command> is currently scanning the heap.  It will prune and
       defragment each page if required, and possibly perform freezing
       activity.  The <structfield>heap_blks_scanned</structfield> column can be used
       to monitor the progress of the scan.
     </entry>
    </row>
    <row>
     <entry><literal>vacuuming indexes</literal></entry>
     <entry>
       <command>VACUUM</command> is currently vacuuming the indexes.  If a table has
       any indexes, this will happen at least once per vacuum, after the heap
       has been completely scanned.  It may happen multiple times per vacuum
       if <xref linkend="guc-maintenance-work-mem"/> is insufficient to
       store the number of dead tuples found.
     </entry>
    </row>
    <row>
     <entry><literal>vacuuming heap</literal></entry>
     <entry>
       <command>VACUUM</command> is currently vacuuming the heap.  Vacuuming the heap
       is distinct from scanning the heap, and occurs after each instance of
       vacuuming indexes.  If <structfield>heap_blks_scanned</structfield> is less than
       <structfield>heap_blks_total</structfield>, the system will return to scanning
       the heap after this phase is completed; otherwise, it will begin
       cleaning up indexes after this phase is completed.
     </entry>
    </row>
    <row>
     <entry><literal>cleaning up indexes</literal></entry>
     <entry>
       <command>VACUUM</command> is currently cleaning up indexes.  This occurs after
       the heap has been completely scanned and all vacuuming of the indexes
       and the heap has been completed.
     </entry>
    </row>
    <row>
     <entry><literal>truncating heap</literal></entry>
     <entry>
       <command>VACUUM</command> is currently truncating the heap so as to return
       empty pages at the end of the relation to the operating system.  This
       occurs after cleaning up indexes.
     </entry>
    </row>
    <row>
     <entry><literal>performing final cleanup</literal></entry>
     <entry>
       <command>VACUUM</command> is performing final cleanup.  During this phase,
       <command>VACUUM</command> will vacuum the free space map, update statistics
       in <literal>pg_class</literal>, and report statistics to the statistics
       collector.  When this phase is completed, <command>VACUUM</command> will end.
     </entry>
    </row>
   </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="cluster-progress-reporting">
  <title>CLUSTER Progress Reporting</title>

  <indexterm>
   <primary>pg_stat_progress_cluster</primary>
  </indexterm>

  <para>
   Whenever <command>CLUSTER</command> or <command>VACUUM FULL</command> is
   running, the <structname>pg_stat_progress_cluster</structname> view will
   contain a row for each backend that is currently running either command.
   The tables below describe the information that will be reported and
   provide information about how to interpret it.
  </para>

  <table id="pg-stat-progress-cluster-view" xreflabel="pg_stat_progress_cluster">
   <title><structname>pg_stat_progress_cluster</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of backend.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the database to which this backend is connected.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>datname</structfield> <type>name</type>
      </para>
      <para>
       Name of the database to which this backend is connected.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the table being clustered.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>command</structfield> <type>text</type>
      </para>
      <para>
       The command that is running. Either <literal>CLUSTER</literal> or <literal>VACUUM FULL</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>phase</structfield> <type>text</type>
      </para>
      <para>
       Current processing phase. See <xref linkend="cluster-phases"/>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>cluster_index_relid</structfield> <type>oid</type>
      </para>
      <para>
       If the table is being scanned using an index, this is the OID of the
       index being used; otherwise, it is zero.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>heap_tuples_scanned</structfield> <type>bigint</type>
      </para>
      <para>
       Number of heap tuples scanned.
       This counter only advances when the phase is
       <literal>seq scanning heap</literal>,
       <literal>index scanning heap</literal>
       or <literal>writing new heap</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>heap_tuples_written</structfield> <type>bigint</type>
      </para>
      <para>
       Number of heap tuples written.
       This counter only advances when the phase is
       <literal>seq scanning heap</literal>,
       <literal>index scanning heap</literal>
       or <literal>writing new heap</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>heap_blks_total</structfield> <type>bigint</type>
      </para>
      <para>
       Total number of heap blocks in the table.  This number is reported
       as of the beginning of <literal>seq scanning heap</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>heap_blks_scanned</structfield> <type>bigint</type>
      </para>
      <para>
       Number of heap blocks scanned.  This counter only advances when the
       phase is <literal>seq scanning heap</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>index_rebuild_count</structfield> <type>bigint</type>
      </para>
      <para>
       Number of indexes rebuilt.  This counter only advances when the phase
       is <literal>rebuilding index</literal>.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="cluster-phases">
   <title>CLUSTER and VACUUM FULL Phases</title>
   <tgroup cols="2">
    <colspec colname="col1" colwidth="1*"/>
    <colspec colname="col2" colwidth="2*"/>
    <thead>
    <row>
      <entry>Phase</entry>
      <entry>Description</entry>
     </row>
    </thead>

   <tbody>
    <row>
     <entry><literal>initializing</literal></entry>
     <entry>
       The command is preparing to begin scanning the heap.  This phase is
       expected to be very brief.
     </entry>
    </row>
    <row>
     <entry><literal>seq scanning heap</literal></entry>
     <entry>
       The command is currently scanning the table using a sequential scan.
     </entry>
    </row>
    <row>
     <entry><literal>index scanning heap</literal></entry>
     <entry>
       <command>CLUSTER</command> is currently scanning the table using an index scan.
     </entry>
    </row>
    <row>
     <entry><literal>sorting tuples</literal></entry>
     <entry>
       <command>CLUSTER</command> is currently sorting tuples.
     </entry>
    </row>
    <row>
     <entry><literal>writing new heap</literal></entry>
     <entry>
       <command>CLUSTER</command> is currently writing the new heap.
     </entry>
    </row>
    <row>
     <entry><literal>swapping relation files</literal></entry>
     <entry>
       The command is currently swapping newly-built files into place.
     </entry>
    </row>
    <row>
     <entry><literal>rebuilding index</literal></entry>
     <entry>
       The command is currently rebuilding an index.
     </entry>
    </row>
    <row>
     <entry><literal>performing final cleanup</literal></entry>
     <entry>
       The command is performing final cleanup.  When this phase is
       completed, <command>CLUSTER</command>
       or <command>VACUUM FULL</command> will end.
     </entry>
    </row>
   </tbody>
   </tgroup>
  </table>
 </sect2>

 <sect2 id="basebackup-progress-reporting">
  <title>Base Backup Progress Reporting</title>

  <indexterm>
   <primary>pg_stat_progress_basebackup</primary>
  </indexterm>

  <para>
   Whenever an application like <application>pg_basebackup</application>
   is taking a base backup, the
   <structname>pg_stat_progress_basebackup</structname>
   view will contain a row for each WAL sender process that is currently
   running the <command>BASE_BACKUP</command> replication command
   and streaming the backup. The tables below describe the information
   that will be reported and provide information about how to interpret it.
  </para>

  <table id="pg-stat-progress-basebackup-view" xreflabel="pg_stat_progress_basebackup">
   <title><structname>pg_stat_progress_basebackup</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of a WAL sender process.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>phase</structfield> <type>text</type>
      </para>
      <para>
       Current processing phase. See <xref linkend="basebackup-phases"/>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>backup_total</structfield> <type>bigint</type>
      </para>
      <para>
       Total amount of data that will be streamed. This is estimated and
       reported as of the beginning of
       <literal>streaming database files</literal> phase. Note that
       this is only an approximation since the database
       may change during <literal>streaming database files</literal> phase
       and WAL log may be included in the backup later. This is always
       the same value as <structfield>backup_streamed</structfield>
       once the amount of data streamed exceeds the estimated
       total size. If the estimation is disabled in
       <application>pg_basebackup</application>
       (i.e., <literal>--no-estimate-size</literal> option is specified),
       this is <literal>NULL</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>backup_streamed</structfield> <type>bigint</type>
      </para>
      <para>
       Amount of data streamed. This counter only advances
       when the phase is <literal>streaming database files</literal> or
       <literal>transferring wal files</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tablespaces_total</structfield> <type>bigint</type>
      </para>
      <para>
       Total number of tablespaces that will be streamed.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>tablespaces_streamed</structfield> <type>bigint</type>
      </para>
      <para>
       Number of tablespaces streamed. This counter only
       advances when the phase is <literal>streaming database files</literal>.
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <table id="basebackup-phases">
   <title>Base backup phases</title>
   <tgroup cols="2">
    <colspec colname="col1" colwidth="1*"/>
    <colspec colname="col2" colwidth="2*"/>
    <thead>
     <row>
      <entry>Phase</entry>
      <entry>Description</entry>
     </row>
    </thead>
    <tbody>
     <row>
      <entry><literal>initializing</literal></entry>
      <entry>
       The WAL sender process is preparing to begin the backup.
       This phase is expected to be very brief.
      </entry>
     </row>
     <row>
      <entry><literal>waiting for checkpoint to finish</literal></entry>
      <entry>
       The WAL sender process is currently performing
       <function>pg_start_backup</function> to prepare to
       take a base backup, and waiting for the start-of-backup
       checkpoint to finish.
      </entry>
     </row>
     <row>
      <entry><literal>estimating backup size</literal></entry>
      <entry>
       The WAL sender process is currently estimating the total amount
       of database files that will be streamed as a base backup.
      </entry>
     </row>
     <row>
      <entry><literal>streaming database files</literal></entry>
      <entry>
       The WAL sender process is currently streaming database files
       as a base backup.
      </entry>
     </row>
     <row>
      <entry><literal>waiting for wal archiving to finish</literal></entry>
      <entry>
       The WAL sender process is currently performing
       <function>pg_stop_backup</function> to finish the backup,
       and waiting for all the WAL files required for the base backup
       to be successfully archived.
       If either <literal>--wal-method=none</literal> or
       <literal>--wal-method=stream</literal> is specified in
       <application>pg_basebackup</application>, the backup will end
       when this phase is completed.
      </entry>
     </row>
     <row>
      <entry><literal>transferring wal files</literal></entry>
      <entry>
       The WAL sender process is currently transferring all WAL logs
       generated during the backup. This phase occurs after
       <literal>waiting for wal archiving to finish</literal> phase if
       <literal>--wal-method=fetch</literal> is specified in
       <application>pg_basebackup</application>. The backup will end
       when this phase is completed.
      </entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>
 </sect1>

 <sect1 id="dynamic-trace">
  <title>Dynamic Tracing</title>

 <indexterm zone="dynamic-trace">
  <primary>DTrace</primary>
 </indexterm>

  <para>
   <productname>PostgreSQL</productname> provides facilities to support
   dynamic tracing of the database server. This allows an external
   utility to be called at specific points in the code and thereby trace
   execution.
  </para>

  <para>
   A number of probes or trace points are already inserted into the source
   code. These probes are intended to be used by database developers and
   administrators. By default the probes are not compiled into
   <productname>PostgreSQL</productname>; the user needs to explicitly tell
   the configure script to make the probes available.
  </para>

  <para>
   Currently, the
   <ulink url="https://en.wikipedia.org/wiki/DTrace">DTrace</ulink>
   utility is supported, which, at the time of this writing, is available
   on Solaris, macOS, FreeBSD, NetBSD, and Oracle Linux.  The
   <ulink url="https://sourceware.org/systemtap/">SystemTap</ulink> project
   for Linux provides a DTrace equivalent and can also be used.  Supporting other dynamic
   tracing utilities is theoretically possible by changing the definitions for
   the macros in <filename>src/include/utils/probes.h</filename>.
  </para>

  <sect2 id="compiling-for-trace">
   <title>Compiling for Dynamic Tracing</title>

  <para>
   By default, probes are not available, so you will need to
   explicitly tell the configure script to make the probes available
   in <productname>PostgreSQL</productname>. To include DTrace support
   specify <option>--enable-dtrace</option> to configure.  See <xref
   linkend="install-procedure"/> for further information.
  </para>
  </sect2>

  <sect2 id="trace-points">
   <title>Built-in Probes</title>

  <para>
   A number of standard probes are provided in the source code,
   as shown in <xref linkend="dtrace-probe-point-table"/>;
   <xref linkend="typedefs-table"/>
   shows the types used in the probes.  More probes can certainly be
   added to enhance <productname>PostgreSQL</productname>'s observability.
  </para>

 <table id="dtrace-probe-point-table">
  <title>Built-in DTrace Probes</title>
  <tgroup cols="3">
   <colspec colname="col1" colwidth="2*"/>
   <colspec colname="col2" colwidth="3*"/>
   <colspec colname="col3" colwidth="3*"/>
   <thead>
    <row>
     <entry>Name</entry>
     <entry>Parameters</entry>
     <entry>Description</entry>
    </row>
   </thead>

   <tbody>

    <row>
     <entry><literal>transaction-start</literal></entry>
     <entry><literal>(LocalTransactionId)</literal></entry>
     <entry>Probe that fires at the start of a new transaction.
      arg0 is the transaction ID.</entry>
    </row>
    <row>
     <entry><literal>transaction-commit</literal></entry>
     <entry><literal>(LocalTransactionId)</literal></entry>
     <entry>Probe that fires when a transaction completes successfully.
      arg0 is the transaction ID.</entry>
    </row>
    <row>
     <entry><literal>transaction-abort</literal></entry>
     <entry><literal>(LocalTransactionId)</literal></entry>
     <entry>Probe that fires when a transaction completes unsuccessfully.
      arg0 is the transaction ID.</entry>
    </row>
    <row>
     <entry><literal>query-start</literal></entry>
     <entry><literal>(const char *)</literal></entry>
     <entry>Probe that fires when the processing of a query is started.
      arg0 is the query string.</entry>
    </row>
    <row>
     <entry><literal>query-done</literal></entry>
     <entry><literal>(const char *)</literal></entry>
     <entry>Probe that fires when the processing of a query is complete.
      arg0 is the query string.</entry>
    </row>
    <row>
     <entry><literal>query-parse-start</literal></entry>
     <entry><literal>(const char *)</literal></entry>
     <entry>Probe that fires when the parsing of a query is started.
      arg0 is the query string.</entry>
    </row>
    <row>
     <entry><literal>query-parse-done</literal></entry>
     <entry><literal>(const char *)</literal></entry>
     <entry>Probe that fires when the parsing of a query is complete.
      arg0 is the query string.</entry>
    </row>
    <row>
     <entry><literal>query-rewrite-start</literal></entry>
     <entry><literal>(const char *)</literal></entry>
     <entry>Probe that fires when the rewriting of a query is started.
      arg0 is the query string.</entry>
    </row>
    <row>
     <entry><literal>query-rewrite-done</literal></entry>
     <entry><literal>(const char *)</literal></entry>
     <entry>Probe that fires when the rewriting of a query is complete.
      arg0 is the query string.</entry>
    </row>
    <row>
     <entry><literal>query-plan-start</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when the planning of a query is started.</entry>
    </row>
    <row>
     <entry><literal>query-plan-done</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when the planning of a query is complete.</entry>
    </row>
    <row>
     <entry><literal>query-execute-start</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when the execution of a query is started.</entry>
    </row>
    <row>
     <entry><literal>query-execute-done</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when the execution of a query is complete.</entry>
    </row>
    <row>
     <entry><literal>statement-status</literal></entry>
     <entry><literal>(const char *)</literal></entry>
     <entry>Probe that fires anytime the server process updates its
      <structname>pg_stat_activity</structname>.<structfield>status</structfield>.
      arg0 is the new status string.</entry>
    </row>
    <row>
     <entry><literal>checkpoint-start</literal></entry>
     <entry><literal>(int)</literal></entry>
     <entry>Probe that fires when a checkpoint is started.
      arg0 holds the bitwise flags used to distinguish different checkpoint
      types, such as shutdown, immediate or force.</entry>
    </row>
    <row>
     <entry><literal>checkpoint-done</literal></entry>
     <entry><literal>(int, int, int, int, int)</literal></entry>
     <entry>Probe that fires when a checkpoint is complete.
      (The probes listed next fire in sequence during checkpoint processing.)
      arg0 is the number of buffers written. arg1 is the total number of
      buffers. arg2, arg3 and arg4 contain the number of WAL files added,
      removed and recycled respectively.</entry>
    </row>
    <row>
     <entry><literal>clog-checkpoint-start</literal></entry>
     <entry><literal>(bool)</literal></entry>
     <entry>Probe that fires when the CLOG portion of a checkpoint is started.
      arg0 is true for normal checkpoint, false for shutdown
      checkpoint.</entry>
    </row>
    <row>
     <entry><literal>clog-checkpoint-done</literal></entry>
     <entry><literal>(bool)</literal></entry>
     <entry>Probe that fires when the CLOG portion of a checkpoint is
      complete. arg0 has the same meaning as for <literal>clog-checkpoint-start</literal>.</entry>
    </row>
    <row>
     <entry><literal>subtrans-checkpoint-start</literal></entry>
     <entry><literal>(bool)</literal></entry>
     <entry>Probe that fires when the SUBTRANS portion of a checkpoint is
      started.
      arg0 is true for normal checkpoint, false for shutdown
      checkpoint.</entry>
    </row>
    <row>
     <entry><literal>subtrans-checkpoint-done</literal></entry>
     <entry><literal>(bool)</literal></entry>
     <entry>Probe that fires when the SUBTRANS portion of a checkpoint is
      complete. arg0 has the same meaning as for
      <literal>subtrans-checkpoint-start</literal>.</entry>
    </row>
    <row>
     <entry><literal>multixact-checkpoint-start</literal></entry>
     <entry><literal>(bool)</literal></entry>
     <entry>Probe that fires when the MultiXact portion of a checkpoint is
      started.
      arg0 is true for normal checkpoint, false for shutdown
      checkpoint.</entry>
    </row>
    <row>
     <entry><literal>multixact-checkpoint-done</literal></entry>
     <entry><literal>(bool)</literal></entry>
     <entry>Probe that fires when the MultiXact portion of a checkpoint is
      complete. arg0 has the same meaning as for
      <literal>multixact-checkpoint-start</literal>.</entry>
    </row>
    <row>
     <entry><literal>buffer-checkpoint-start</literal></entry>
     <entry><literal>(int)</literal></entry>
     <entry>Probe that fires when the buffer-writing portion of a checkpoint
      is started.
      arg0 holds the bitwise flags used to distinguish different checkpoint
      types, such as shutdown, immediate or force.</entry>
    </row>
    <row>
     <entry><literal>buffer-sync-start</literal></entry>
     <entry><literal>(int, int)</literal></entry>
     <entry>Probe that fires when we begin to write dirty buffers during
      checkpoint (after identifying which buffers must be written).
      arg0 is the total number of buffers.
      arg1 is the number that are currently dirty and need to be written.</entry>
    </row>
    <row>
     <entry><literal>buffer-sync-written</literal></entry>
     <entry><literal>(int)</literal></entry>
     <entry>Probe that fires after each buffer is written during checkpoint.
      arg0 is the ID number of the buffer.</entry>
    </row>
    <row>
     <entry><literal>buffer-sync-done</literal></entry>
     <entry><literal>(int, int, int)</literal></entry>
     <entry>Probe that fires when all dirty buffers have been written.
      arg0 is the total number of buffers.
      arg1 is the number of buffers actually written by the checkpoint process.
      arg2 is the number that were expected to be written (arg1 of
      <literal>buffer-sync-start</literal>); any difference reflects other processes flushing
      buffers during the checkpoint.</entry>
    </row>
    <row>
     <entry><literal>buffer-checkpoint-sync-start</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires after dirty buffers have been written to the
      kernel, and before starting to issue fsync requests.</entry>
    </row>
    <row>
     <entry><literal>buffer-checkpoint-done</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when syncing of buffers to disk is
      complete.</entry>
    </row>
    <row>
     <entry><literal>twophase-checkpoint-start</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when the two-phase portion of a checkpoint is
      started.</entry>
    </row>
    <row>
     <entry><literal>twophase-checkpoint-done</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when the two-phase portion of a checkpoint is
      complete.</entry>
    </row>
    <row>
     <entry><literal>buffer-read-start</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid, int, bool)</literal></entry>
     <entry>Probe that fires when a buffer read is started.
      arg0 and arg1 contain the fork and block numbers of the page (but
      arg1 will be -1 if this is a relation extension request).
      arg2, arg3, and arg4 contain the tablespace, database, and relation OIDs
      identifying the relation.
      arg5 is the ID of the backend which created the temporary relation for a
      local buffer, or <symbol>InvalidBackendId</symbol> (-1) for a shared buffer.
      arg6 is true for a relation extension request, false for normal
      read.</entry>
    </row>
    <row>
     <entry><literal>buffer-read-done</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid, int, bool, bool)</literal></entry>
     <entry>Probe that fires when a buffer read is complete.
      arg0 and arg1 contain the fork and block numbers of the page (if this
      is a relation extension request, arg1 now contains the block number
      of the newly added block).
      arg2, arg3, and arg4 contain the tablespace, database, and relation OIDs
      identifying the relation.
      arg5 is the ID of the backend which created the temporary relation for a
      local buffer, or <symbol>InvalidBackendId</symbol> (-1) for a shared buffer.
      arg6 is true for a relation extension request, false for normal
      read.
      arg7 is true if the buffer was found in the pool, false if not.</entry>
    </row>
    <row>
     <entry><literal>buffer-flush-start</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid)</literal></entry>
     <entry>Probe that fires before issuing any write request for a shared
      buffer.
      arg0 and arg1 contain the fork and block numbers of the page.
      arg2, arg3, and arg4 contain the tablespace, database, and relation OIDs
      identifying the relation.</entry>
    </row>
    <row>
     <entry><literal>buffer-flush-done</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid)</literal></entry>
     <entry>Probe that fires when a write request is complete.  (Note
      that this just reflects the time to pass the data to the kernel;
      it's typically not actually been written to disk yet.)
      The arguments are the same as for <literal>buffer-flush-start</literal>.</entry>
    </row>
    <row>
     <entry><literal>buffer-write-dirty-start</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid)</literal></entry>
     <entry>Probe that fires when a server process begins to write a dirty
      buffer.  (If this happens often, it implies that
      <xref linkend="guc-shared-buffers"/> is too
      small or the background writer control parameters need adjustment.)
      arg0 and arg1 contain the fork and block numbers of the page.
      arg2, arg3, and arg4 contain the tablespace, database, and relation OIDs
      identifying the relation.</entry>
    </row>
    <row>
     <entry><literal>buffer-write-dirty-done</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid)</literal></entry>
     <entry>Probe that fires when a dirty-buffer write is complete.
      The arguments are the same as for <literal>buffer-write-dirty-start</literal>.</entry>
    </row>
    <row>
     <entry><literal>wal-buffer-write-dirty-start</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when a server process begins to write a
      dirty WAL buffer because no more WAL buffer space is available.
      (If this happens often, it implies that
      <xref linkend="guc-wal-buffers"/> is too small.)</entry>
    </row>
    <row>
     <entry><literal>wal-buffer-write-dirty-done</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when a dirty WAL buffer write is complete.</entry>
    </row>
    <row>
     <entry><literal>wal-insert</literal></entry>
     <entry><literal>(unsigned char, unsigned char)</literal></entry>
     <entry>Probe that fires when a WAL record is inserted.
      arg0 is the resource manager (rmid) for the record.
      arg1 contains the info flags.</entry>
    </row>
    <row>
     <entry><literal>wal-switch</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when a WAL segment switch is requested.</entry>
    </row>
    <row>
     <entry><literal>smgr-md-read-start</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid, int)</literal></entry>
     <entry>Probe that fires when beginning to read a block from a relation.
      arg0 and arg1 contain the fork and block numbers of the page.
      arg2, arg3, and arg4 contain the tablespace, database, and relation OIDs
      identifying the relation.
      arg5 is the ID of the backend which created the temporary relation for a
      local buffer, or <symbol>InvalidBackendId</symbol> (-1) for a shared buffer.</entry>
    </row>
    <row>
     <entry><literal>smgr-md-read-done</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid, int, int, int)</literal></entry>
     <entry>Probe that fires when a block read is complete.
      arg0 and arg1 contain the fork and block numbers of the page.
      arg2, arg3, and arg4 contain the tablespace, database, and relation OIDs
      identifying the relation.
      arg5 is the ID of the backend which created the temporary relation for a
      local buffer, or <symbol>InvalidBackendId</symbol> (-1) for a shared buffer.
      arg6 is the number of bytes actually read, while arg7 is the number
      requested (if these are different it indicates trouble).</entry>
    </row>
    <row>
     <entry><literal>smgr-md-write-start</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid, int)</literal></entry>
     <entry>Probe that fires when beginning to write a block to a relation.
      arg0 and arg1 contain the fork and block numbers of the page.
      arg2, arg3, and arg4 contain the tablespace, database, and relation OIDs
      identifying the relation.
      arg5 is the ID of the backend which created the temporary relation for a
      local buffer, or <symbol>InvalidBackendId</symbol> (-1) for a shared buffer.</entry>
    </row>
    <row>
     <entry><literal>smgr-md-write-done</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid, int, int, int)</literal></entry>
     <entry>Probe that fires when a block write is complete.
      arg0 and arg1 contain the fork and block numbers of the page.
      arg2, arg3, and arg4 contain the tablespace, database, and relation OIDs
      identifying the relation.
      arg5 is the ID of the backend which created the temporary relation for a
      local buffer, or <symbol>InvalidBackendId</symbol> (-1) for a shared buffer.
      arg6 is the number of bytes actually written, while arg7 is the number
      requested (if these are different it indicates trouble).</entry>
    </row>
    <row>
     <entry><literal>sort-start</literal></entry>
     <entry><literal>(int, bool, int, int, bool, int)</literal></entry>
     <entry>Probe that fires when a sort operation is started.
      arg0 indicates heap, index or datum sort.
      arg1 is true for unique-value enforcement.
      arg2 is the number of key columns.
      arg3 is the number of kilobytes of work memory allowed.
      arg4 is true if random access to the sort result is required.
      arg5 indicates serial when <literal>0</literal>, parallel worker when
      <literal>1</literal>, or parallel leader when <literal>2</literal>.</entry>
    </row>
    <row>
     <entry><literal>sort-done</literal></entry>
     <entry><literal>(bool, long)</literal></entry>
     <entry>Probe that fires when a sort is complete.
      arg0 is true for external sort, false for internal sort.
      arg1 is the number of disk blocks used for an external sort,
      or kilobytes of memory used for an internal sort.</entry>
    </row>
    <row>
     <entry><literal>lwlock-acquire</literal></entry>
     <entry><literal>(char *, LWLockMode)</literal></entry>
     <entry>Probe that fires when an LWLock has been acquired.
      arg0 is the LWLock's tranche.
      arg1 is the requested lock mode, either exclusive or shared.</entry>
    </row>
    <row>
     <entry><literal>lwlock-release</literal></entry>
     <entry><literal>(char *)</literal></entry>
     <entry>Probe that fires when an LWLock has been released (but note
      that any released waiters have not yet been awakened).
      arg0 is the LWLock's tranche.</entry>
    </row>
    <row>
     <entry><literal>lwlock-wait-start</literal></entry>
     <entry><literal>(char *, LWLockMode)</literal></entry>
     <entry>Probe that fires when an LWLock was not immediately available and
      a server process has begun to wait for the lock to become available.
      arg0 is the LWLock's tranche.
      arg1 is the requested lock mode, either exclusive or shared.</entry>
    </row>
    <row>
     <entry><literal>lwlock-wait-done</literal></entry>
     <entry><literal>(char *, LWLockMode)</literal></entry>
     <entry>Probe that fires when a server process has been released from its
      wait for an LWLock (it does not actually have the lock yet).
      arg0 is the LWLock's tranche.
      arg1 is the requested lock mode, either exclusive or shared.</entry>
    </row>
    <row>
     <entry><literal>lwlock-condacquire</literal></entry>
     <entry><literal>(char *, LWLockMode)</literal></entry>
     <entry>Probe that fires when an LWLock was successfully acquired when the
      caller specified no waiting.
      arg0 is the LWLock's tranche.
      arg1 is the requested lock mode, either exclusive or shared.</entry>
    </row>
    <row>
     <entry><literal>lwlock-condacquire-fail</literal></entry>
     <entry><literal>(char *, LWLockMode)</literal></entry>
     <entry>Probe that fires when an LWLock was not successfully acquired when
      the caller specified no waiting.
      arg0 is the LWLock's tranche.
      arg1 is the requested lock mode, either exclusive or shared.</entry>
    </row>
    <row>
     <entry><literal>lock-wait-start</literal></entry>
     <entry><literal>(unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, LOCKMODE)</literal></entry>
     <entry>Probe that fires when a request for a heavyweight lock (lmgr lock)
      has begun to wait because the lock is not available.
      arg0 through arg3 are the tag fields identifying the object being
      locked.  arg4 indicates the type of object being locked.
      arg5 indicates the lock type being requested.</entry>
    </row>
    <row>
     <entry><literal>lock-wait-done</literal></entry>
     <entry><literal>(unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, LOCKMODE)</literal></entry>
     <entry>Probe that fires when a request for a heavyweight lock (lmgr lock)
      has finished waiting (i.e., has acquired the lock).
      The arguments are the same as for <literal>lock-wait-start</literal>.</entry>
    </row>
    <row>
     <entry><literal>deadlock-found</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when a deadlock is found by the deadlock
      detector.</entry>
    </row>

   </tbody>
   </tgroup>
  </table>

 <table id="typedefs-table">
  <title>Defined Types Used in Probe Parameters</title>
  <tgroup cols="2">
   <thead>
    <row>
     <entry>Type</entry>
     <entry>Definition</entry>
    </row>
   </thead>

   <tbody>

    <row>
     <entry><type>LocalTransactionId</type></entry>
     <entry><type>unsigned int</type></entry>
    </row>
    <row>
     <entry><type>LWLockMode</type></entry>
     <entry><type>int</type></entry>
    </row>
    <row>
     <entry><type>LOCKMODE</type></entry>
     <entry><type>int</type></entry>
    </row>
    <row>
     <entry><type>BlockNumber</type></entry>
     <entry><type>unsigned int</type></entry>
    </row>
    <row>
     <entry><type>Oid</type></entry>
     <entry><type>unsigned int</type></entry>
    </row>
    <row>
     <entry><type>ForkNumber</type></entry>
     <entry><type>int</type></entry>
    </row>
    <row>
     <entry><type>bool</type></entry>
     <entry><type>unsigned char</type></entry>
    </row>

   </tbody>
   </tgroup>
  </table>


  </sect2>

  <sect2 id="using-trace-points">
   <title>Using Probes</title>

  <para>
   The example below shows a DTrace script for analyzing transaction
   counts in the system, as an alternative to snapshotting
   <structname>pg_stat_database</structname> before and after a performance test:
<programlisting>
#!/usr/sbin/dtrace -qs

postgresql$1:::transaction-start
{
      @start["Start"] = count();
      self->ts  = timestamp;
}

postgresql$1:::transaction-abort
{
      @abort["Abort"] = count();
}

postgresql$1:::transaction-commit
/self->ts/
{
      @commit["Commit"] = count();
      @time["Total time (ns)"] = sum(timestamp - self->ts);
      self->ts=0;
}
</programlisting>
   When executed, the example D script gives output such as:
<screen>
# ./txn_count.d `pgrep -n postgres` or ./txn_count.d &lt;PID&gt;
^C

Start                                          71
Commit                                         70
Total time (ns)                        2312105013
</screen>
  </para>

  <note>
   <para>
    SystemTap uses a different notation for trace scripts than DTrace does,
    even though the underlying trace points are compatible.  One point worth
    noting is that at this writing, SystemTap scripts must reference probe
    names using double underscores in place of hyphens.  This is expected to
    be fixed in future SystemTap releases.
   </para>
  </note>

  <para>
   You should remember that DTrace scripts need to be carefully written and
   debugged, otherwise the trace information collected might
   be meaningless. In most cases where problems are found it is the
   instrumentation that is at fault, not the underlying system. When
   discussing information found using dynamic tracing, be sure to enclose
   the script used to allow that too to be checked and discussed.
  </para>
  </sect2>

  <sect2 id="defining-trace-points">
   <title>Defining New Probes</title>

  <para>
   New probes can be defined within the code wherever the developer
   desires, though this will require a recompilation. Below are the steps
   for inserting new probes:
  </para>

  <procedure>
   <step>
    <para>
     Decide on probe names and data to be made available through the probes
    </para>
   </step>

   <step>
    <para>
     Add the probe definitions to <filename>src/backend/utils/probes.d</filename>
    </para>
   </step>

   <step>
    <para>
     Include <filename>pg_trace.h</filename> if it is not already present in the
     module(s) containing the probe points, and insert
     <literal>TRACE_POSTGRESQL</literal> probe macros at the desired locations
     in the source code
    </para>
   </step>

   <step>
    <para>
     Recompile and verify that the new probes are available
    </para>
   </step>
  </procedure>

  <formalpara>
   <title>Example:</title>
   <para>
    Here is an example of how you would add a probe to trace all new
    transactions by transaction ID.
   </para>
  </formalpara>

  <procedure>
   <step>
    <para>
     Decide that the probe will be named <literal>transaction-start</literal> and
     requires a parameter of type <type>LocalTransactionId</type>
    </para>
   </step>

   <step>
    <para>
     Add the probe definition to <filename>src/backend/utils/probes.d</filename>:
<programlisting>
probe transaction__start(LocalTransactionId);
</programlisting>
     Note the use of the double underline in the probe name. In a DTrace
     script using the probe, the double underline needs to be replaced with a
     hyphen, so <literal>transaction-start</literal> is the name to document for
     users.
    </para>
   </step>

   <step>
    <para>
     At compile time, <literal>transaction__start</literal> is converted to a macro
     called <literal>TRACE_POSTGRESQL_TRANSACTION_START</literal> (notice the
     underscores are single here), which is available by including
     <filename>pg_trace.h</filename>.  Add the macro call to the appropriate location
     in the source code.  In this case, it looks like the following:

<programlisting>
TRACE_POSTGRESQL_TRANSACTION_START(vxid.localTransactionId);
</programlisting>
    </para>
   </step>

   <step>
    <para>
     After recompiling and running the new binary, check that your newly added
     probe is available by executing the following DTrace command.  You
     should see similar output:
<screen>
# dtrace -ln transaction-start
   ID    PROVIDER          MODULE           FUNCTION NAME
18705 postgresql49878     postgres     StartTransactionCommand transaction-start
18755 postgresql49877     postgres     StartTransactionCommand transaction-start
18805 postgresql49876     postgres     StartTransactionCommand transaction-start
18855 postgresql49875     postgres     StartTransactionCommand transaction-start
18986 postgresql49873     postgres     StartTransactionCommand transaction-start
</screen>
    </para>
   </step>
  </procedure>

  <para>
   There are a few things to be careful about when adding trace macros
   to the C code:

   <itemizedlist>
    <listitem>
     <para>
      You should take care that the data types specified for a probe's
      parameters match the data types of the variables used in the macro.
      Otherwise, you will get compilation errors.
     </para>
    </listitem>


    <listitem>
     <para>
      On most platforms, if <productname>PostgreSQL</productname> is
      built with <option>--enable-dtrace</option>, the arguments to a trace
      macro will be evaluated whenever control passes through the
      macro, <emphasis>even if no tracing is being done</emphasis>.  This is
      usually not worth worrying about if you are just reporting the
      values of a few local variables.  But beware of putting expensive
      function calls into the arguments.  If you need to do that,
      consider protecting the macro with a check to see if the trace
      is actually enabled:

<programlisting>
if (TRACE_POSTGRESQL_TRANSACTION_START_ENABLED())
    TRACE_POSTGRESQL_TRANSACTION_START(some_function(...));
</programlisting>

      Each trace macro has a corresponding <literal>ENABLED</literal> macro.
     </para>
    </listitem>
   </itemizedlist>

  </para>

  </sect2>

 </sect1>

</chapter>
