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<Chapter Id="runtime">
 <Title>Server Runtime Environment</Title>

 <Para>
  This chapter discusses how to set up and run the database server
  and the interactions with the operating system.
 </para>

 <sect1 id="postgres-user">
  <title>The Postgres user account</title>

  <para>
   As with any other server daemon that is connected to the world at
   large, it is advisable to run Postgres under a separate user
   account. This user account should only own the data itself that is
   being managed by the server, and should not be shared with other
   daemons. (Thus, using the user <quote>nobody</quote> is a bad
   idea.) It is not advisable to install the executables as owned by
   this user account because that runs the risk of user-defined
   functions gone astray or any other exploits compromising the
   executable programs.
  </para>
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  <para>
   To add a user account to your system, look for a command
   <command>useradd</command> or <command>adduser</command>. The user
   name <quote>postgres</quote> is often used but by no means
   required.
  </para>
 </sect1>

 <sect1 id="creating-cluster">
  <title>Creating a database cluster</title>

  <para>
   Before you can do anything, you must initialize a database storage
   area on disk. We call this a <firstterm>database
   cluster</firstterm>. (<acronym>SQL</acronym> speaks of a catalog
   cluster instead.) A database cluster is a collection of databases
   that will be accessible through a single instance of a running
   database server. After initialization, a database cluster will
   contain one database named <literal>template1</literal>. As the
   name suggests, this will be used as a template for any subsequently
   created database; it should not be used for actual work.
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  </para>

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  <para>
   In file system terms, a database cluster will be a single directory
   under which all data will be stored. We call this the
   <firstterm>data directory</firstterm> or <firstterm>data
   area</firstterm>. It is completely up to you where you choose to
   store your data, there is no default, although locations such as
   <filename>/usr/local/pgsql/data</filename> or
   <filename>/var/lib/pgsql/data</filename> are popular. To initialize
   a database cluster, use the command <command>initdb</command>,
   which is installed with <productname>PostgreSQL</productname>. The
   desired file system location of your database system is indicated
   by the <option>-D</option> option, for example
<screen>
&gt; <userinput>initdb -D /usr/local/pgsql/data</userinput>
</screen>
   Note that you must execute this command while being logged in to
   the Postgres user account, which is described in the previous
   section.
  </para>
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  <tip>
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   <para>
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    As an alternative to the <option>-D</option> option, you can set
    the environment variable <envar>PGDATA</envar>.
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   </para>
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  </tip>

  <para>
   <command>initdb</command> will attempt to create the directory you
   specify if it does not already exist. It is likely that it won't
   have the permission to do so (if you followed our advice and
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   created an unprivileged account). In that case you should create the
   directory yourself (as root) and transfer ownership of it to the
   Postgres user account. Here is how this might work:
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<screen>
root# <userinput>mkdir /usr/local/pgsql/data</userinput>
root# <userinput>chown postgres /usr/local/pgsql/data</userinput>
root# <userinput>su postgres</userinput>
postgres&gt; <userinput>initdb -D /usr/local/pgsql/data</userinput>
</screen>
  </para>
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  <para>
   <command>initdb</command> will refuse to run if the data directory
   looks like it belongs to an already initialized installation.
  </para>

  <para>
   Because the data directory contains all the data stored in the
   database it is essential that it be well secured from unauthorized
   access. <command>initdb</command> therefore revokes access
   permissions from everyone but the Postgres user account.
  </para>
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  <para>
   One surprise you might encounter while running <command>initdb</command> is
   a notice similar to this one:
<screen>
NOTICE:  Initializing database with en_US collation order.
        This locale setting will prevent use of index optimization for
        LIKE and regexp searches.  If you are concerned about speed of
        such queries, you may wish to set LC_COLLATE to "C" and
        re-initdb.  For more information see the Administrator's Guide.
</screen>
   This notice is intended to warn you that the currently selected locale
   will cause indexes to be sorted in an order that prevents them from
   being used for LIKE and regular-expression searches.  If you need
   good performance of such searches, you should set your current locale
   to "C" and re-run <command>initdb</command>.  On most systems, setting the
   current locale is done by changing the value of the environment variable
   <literal>LC_ALL</literal> or <literal>LANG</literal>.  The sort order used
   within a particular database cluster is set by <command>initdb</command>
   and cannot be changed later, short of dumping all data, re-initdb,
   reload data.  So it's important to make this choice correctly now.
  </para>
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 </sect1>

 <sect1 id="postmaster-start">
  <title>Starting the database server</title>

  <para>
   Before anyone can access the database you must start the database
   server. The database server is called
   <firstterm>postmaster</firstterm>.
   The postmaster must know where to find the data it is supposed
   to work on. This is done with the <option>-D</option> option. Thus,
   the simplest way to start the server is, for example,
<screen>
&gt; <userinput>postmaster -D /usr/local/pgsql/data</userinput>
</screen>
   which will leave the server running in the foreground. This must
   again be done while logged in to the Postgres user account. Without
   a <option>-D</option>, the server will try to use the data
   directory in the environment variable <envar>PGDATA</envar>; if
   neither of these works it will fail.
  </para>

  <para>
   To start the <application>postmaster</application> in the
   background, use the usual shell syntax:
<screen>
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&gt; <userinput>postmaster -D /usr/local/pgsql/data &gt; logfile 2&gt;&amp;1 &amp;</userinput>
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</screen>
   It is an extremely good idea to keep the server output around
   somewhere, as indicated here. It will help both for auditing
   purposes and to diagnose problems.
  </para>

  <para>
   The postmaster also takes a number of other command line options.
   For more information see the reference page and below under runtime
   configuration. In particular, in order for the postmaster to accept
   TCP/IP connections (rather than just Unix domain socket ones), you
   must also specify the <option>-i</option> option.
  </para>

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  <para>
   This shells syntax can get tedious quickly.  Therefore the shell
   script wrapper <application>pg_ctl</application> is provided that
   encapsulates some of the tasks.  E.g.,
<programlisting>
pg_ctl start -l logfile
</programlisting>
   will start the server in the background and put the output into the
   named log file.  The <option>-D</option> option has the same
   meaning as when invoking postmaster directly.
   <application>pg_ctl</application> also implements a symmetric
   <quote>stop</quote> operation.
  </para>

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  <para>
   Normally, you will want to start the database server when the
   computer boots up. This is not required; the
   <productname>PostgreSQL</productname> server can be run
   successfully from non-privileged accounts without root
   intervention.
  </para>

  <para>
   Different systems have different conventions for starting up
   daemons at boot time, so you are advised to familiarize yourself
   with them. Many systems have a file
   <filename>/etc/rc.local</filename> or
   <filename>/etc/rc.d/rc.local</filename> which is almost certainly
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   no bad place to put such a command. Whatever you do, the server
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   must be run by the <productname>Postgres</productname> user account
   <emphasis>and not by root</emphasis> or any other user. Therefore
   you probably always want to form your command lines along the lines
   of <literal>su -c '...' postgres</literal>, for example:
<programlisting>
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su -c 'pg_ctl -D /usr/local/pgsql/data -l serverlog' postgres
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</programlisting>
  </para>

  <para>
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   Here are a few more operating system specific suggestions.  (Always
   replace the proper installation directory and the user name you
   chose.)
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   <itemizedlist>
    <listitem>
     <para>
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      For <productname>FreeBSD</productname>, take a look at the file
      <filename>contrib/start-scripts/freebsd</filename> in the
      <productname>PostgreSQL</productname> source distribution.
     </para>
    </listitem>

    <listitem>
     <para>
      On <productname>OpenBSD</productname>, add the following lines
      to the file <filename>/etc/rc.local</filename>:
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<programlisting>
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if [ -x /usr/local/pgsql/bin/pg_ctl -a -x /usr/local/pgsql/bin/postmaster ]; then
    su - -c '/usr/local/pgsql/bin/pg_ctl start -l /var/postgresql/log -s' postgres
    echo -n ' postgresql'
fi
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</programlisting>
     </para>
    </listitem>

    <listitem>
     <para>
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      On <productname>Linux</productname> systems either add
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<programlisting>
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/usr/local/pgsql/bin/pg_ctl start -l logfile -D /usr/local/pgsql/data
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</programlisting>
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      to <filename>/etc/rc.d/rc.local</filename> or look into the file
      <filename>contrib/start-scripts/linux</filename> in the
      <productname>PostgreSQL</productname> source distribution to
      integrate the start and shutdown into the run level system.
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     </para>
    </listitem>

    <listitem>
     <para>
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      On <productname>NetBSD</productname>, either use the
      <productname>FreeBSD</productname> or
      <productname>Linux</productname> start scripts, depending on
      preference, as an example and place the file at
      <filename>/usr/local/etc/rc.d/postgresql</filename>.
     </para>
    </listitem>

    <listitem>
     <para>
      On <productname>Solaris</productname>, edit the file
      <filename>rc2.d</filename> to contain the following single line:
<programlisting>
su - postgres -c "/usr/local/pgsql/bin/pg_ctl start -l logfile -D /usr/local/pgsql/data"
</programlisting>
     </para>
    </listitem>
   </itemizedlist>

  </para>
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   <para>
    While the <application>postmaster</application> is running, it's
    PID is in the file <filename>postmaster.pid</filename> in the data
    directory. This is used as in interlock against multiple running
    postmaster on the same data directory and can also be used for
    shutting down the postmaster.
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   </para>

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   <sect2 id="postmaster-start-failures">
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    <title>Server Start-up Failures</title>
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    <para>
     There are several common reasons for the postmaster to fail to
     start up. Check the postmaster's log file, or start it by hand
     (without redirecting standard output or standard error) to see
     what complaint messages appear. Some of the possible error
     messages are reasonably self-explanatory, but here are some that
     are not.
    </para>

    <para>
<screen>
FATAL: StreamServerPort: bind() failed: Address already in use
        Is another postmaster already running on that port?
</screen>
     This usually means just what it suggests: you accidentally
     started a second postmaster on the same port where one is already
     running. However, if the kernel error message is not
     <computeroutput>Address already in use</computeroutput> or some
     variant of that wording, there may be a different problem. For
     example, trying to start a postmaster on a reserved port number
     may draw something like
<screen>
&gt; <userinput>postmaster -i -p 666</userinput>
FATAL: StreamServerPort: bind() failed: Permission denied
        Is another postmaster already running on that port?
</screen>
    </para>

    <para>
     A message like
<screen>
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IpcMemoryCreate: shmget(key=5440001, size=83918612, 01600) failed: Invalid argument
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FATAL 1:  ShmemCreate: cannot create region
</screen>
     probably means that your kernel's limit on the size of shared
     memory areas is smaller than the buffer area that Postgres is
     trying to create (83918612 bytes in this example). Or it could
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     mean that you don't have System-V-style shared memory support
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     configured into your kernel at all. As a temporary workaround,
     you can try starting the postmaster with a smaller-than-normal
     number of buffers (<option>-B</option> switch). You will
     eventually want to reconfigure your kernel to increase the
     allowed shared memory size, however. You may see this message
     when trying to start multiple postmasters on the same machine, if
     their total space requests exceed the kernel limit.
    </para>

    <para>
     An error like
<screen>
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IpcSemaphoreCreate: semget(key=5440026, num=16, 01600) failed: No space left on device
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</screen>
     does <emphasis>not</emphasis> mean that you've run out of disk
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     space; it means that your kernel's limit on the number of System
     V semaphores is smaller than the number
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     <productname>Postgres</productname> wants to create. As above,
     you may be able to work around the problem by starting the
     postmaster with a reduced number of backend processes
     (<option>-N</option> switch), but you'll eventually want to
     increase the kernel limit.
    </para>
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Peter Eisentraut committed
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    <para>
     If you get an <quote>illegal system call</> error, then it is likely that
     shared memory or semaphores are not supported at all in your kernel. In
     that case your only option is to re-configure the kernel to turn on these
     features.
    </para>

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    <para>
     Details about configuring System V IPC facilities are given in
     <xref linkend="sysvipc">.
    </para>
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   </sect2>

   <sect2 id="client-connection-problems">
    <title>Client Connection Problems</title>

    <para>
     Although the possible error conditions on the client side are
     both virtually infinite and application dependent, a few of them
     might be directly related to how the server was started up.
     Conditions other than those shown below should be documented with
     the respective client application.
    </para>

    <para>
<screen>
connectDB() -- connect() failed: Connection refused
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Is the postmaster running (with -i) at 'server.joe.com' and accepting connections on TCP/IP port 5432?
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</screen>
     This is the generic <quote>I couldn't find a server to talk
     to</quote> failure. It looks like the above when TCP/IP
     communication is attempted. A common mistake is to forget the
     <option>-i</option> to the postmaster to allow TCP/IP
     connections.
    </para>

    <para>
     Alternatively, you'll get this when attempting
     Unix-socket communication to a local postmaster:
<screen>
connectDB() -- connect() failed: No such file or directory
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Is the postmaster running locally and accepting connections on Unix socket '/tmp/.s.PGSQL.5432'?
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</screen>
    </para>

    <para>
     The last line is useful in verifying that the client is trying to
     connect where it is supposed to. If there is in fact no
     postmaster running there, the kernel error message will typically
     be either <computeroutput>Connection refused</computeroutput> or
     <computeroutput>No such file or directory</computeroutput>, as
     illustrated. (It is particularly important to realize that
     <computeroutput>Connection refused</computeroutput> in this
     context does <emphasis>not</emphasis> mean that the postmaster
     got your connection request and rejected it -- that case will
     produce a different message, as shown in <xref
     linkend="client-authentication-problems">.) Other error messages
     such as <computeroutput>Connection timed out</computeroutput> may
     indicate more fundamental problems, like lack of network
     connectivity.
    </para>
   </sect2>
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  </sect1>

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  <sect1 id="runtime-config">
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   <Title>Run-time configuration</Title>
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   <para>
    There are a lot of configuration parameters that affect the
    behavior of the database system in some way or other. Here we
    describe how to set them and the following subsections will
    discuss each of them.
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   </para>

   <para>
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    All parameter names are case-insensitive. Every parameter takes a
    value of one of the four types boolean, integer, floating point,
    string as described below. Boolean values are
    <literal>ON</literal>, <literal>OFF</literal>,
    <literal>TRUE</literal>, <literal>FALSE</literal>,
    <literal>YES</literal>, <literal>NO</literal>,
    <literal>1</literal>, <literal>0</literal> (case-insensitive) or
    any non-ambiguous prefix of these.
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   </para>

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   <para>
    One way to set these options is to create a file
    <filename>postgresql.conf</filename> in the data directory (e.g.,
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    <filename>/usr/local/pgsql/data</filename>). An example of what
    this file could look like is:
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<programlisting>
# This is a comment
log_connections = yes
syslog = 2
</programlisting>
    As you see, options are one per line. The equal sign between name
    and value is optional. White space is insignificant, blank lines
    are ignored. Hash marks (<quote>#</quote>) introduce comments
    anywhere.
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   </para>

   <para>
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    The configuration file is reread whenever the postmaster receives
    a SIGHUP signal. This signal is also propagated to all running
    backend processes, so that running sessions get the new default.
    Alternatively, you can send the signal to only one backend process
    directly.
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   </para>

   <para>
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    A second way to set these configuration parameters is to give them
    as a command line option to the postmaster, such as
<programlisting>
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postmaster -c log_connections=yes -c syslog=2
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</programlisting>
    which would have the same effect as the previous example.
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   </para>

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   <para>
    Occasionally it is also useful to give a command line option to
    one particular backend session only. The environment variable
    <envar>PGOPTIONS</envar> can be used for this purpose on the
    client side:
<programlisting>
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env PGOPTIONS='-c geqo=off' psql
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</programlisting>
    (This works for any client application, not just
    <application>psql</application>.) Note that this won't work for
    options that are necessarily fixed once the server is started,
    such as the port number.
   </para>
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   <para>
    Finally, some options can be changed in individual SQL sessions
    with the <command>SET</command> command, for example
<screen>
=&gt; <userinput>SET ENABLE_SEQSCAN TO OFF;</userinput>
</screen>
    See the SQL command language reference for details on the syntax.
   </para>
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   <sect2 id="runtime-config-optimizer">
    <title>Planner and Optimizer Tuning</title>
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   <para>
    <variablelist>
     <varlistentry>
      <term>CPU_INDEX_TUPLE_COST (<type>floating point</type>)</term>
      <listitem>
       <para>
        Sets the query optimizer's estimate of the cost of processing
	each index tuple during an index scan. This is measured as a
	fraction of the cost of a sequential page fetch.
       </para>
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      </listitem>
     </varlistentry>
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     <varlistentry>
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      <term>CPU_OPERATOR_COST (<type>floating point</type>)</term>
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      <listitem>
       <para>
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        Sets the optimizer's estimate of the cost of processing each
	operator in a WHERE clause. This is measured as a fraction of
	the cost of a sequential page fetch.
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       </para>
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      </listitem>
     </varlistentry>
    
     <varlistentry>
      <term>CPU_TUPLE_COST (<type>floating point</type>)</term>
      <listitem>
       <para>
        Sets the query optimizer's estimate of the cost of processing
	each tuple during a query. This is measured as a fraction of
	the cost of a sequential page fetch.
       </para>
      </listitem>
     </varlistentry>
    
     <varlistentry>
      <term>EFFECTIVE_CACHE_SIZE (<type>floating point</type>)</term>
      <listitem>
       <para>
        Sets the optimizer's assumption about the effective size of
	the disk cache (that is, the portion of the kernel's disk
	cache that will be used for
	<productname>Postgres</productname> data files). This is
	measured in disk pages, which are normally 8kB apiece.
       </para>
      </listitem>
     </varlistentry>
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     <varlistentry>
      <term>ENABLE_HASHJOIN (<type>boolean</type>)</term>
      <listitem>
       <para>
        Enables or disables the query planner's use of hash-join plan
        types. The default is on. This is mostly useful to debug the
        query planner.
       </para>
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      </listitem>
     </varlistentry>

     <varlistentry>
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      <term>ENABLE_INDEXSCAN (<type>boolean</type>)</term>
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      <listitem>
       <para>
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        Enables or disables the query planner's use of index scan plan
        types. The default is on. This is mostly useful to debug the
        query planner.
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       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
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      <term>ENABLE_MERGEJOIN (<type>boolean</type>)</term>
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      <listitem>
       <para>
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        Enables or disables the query planner's use of merge-join plan
        types. The default is on. This is mostly useful to debug the
        query planner.
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       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
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      <term>ENABLE_NESTLOOP (<type>boolean</type>)</term>
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      <listitem>
       <para>
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        Enables or disables the query planner's use of nested-loop
	join plans. It's not possible to suppress nested-loop joins
	entirely, but turning this variable off discourages the
	planner from using one if there is any other method available.
	The default is on. This is mostly useful to debug the query
	planner.
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       </para>
      </listitem>
     </varlistentry>

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     <varlistentry>
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      <term>ENABLE_SEQSCAN (<type>boolean</type>)</term>
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      <listitem>
       <para>
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        Enables or disables the query planner's use of sequential scan
	plan types. It's not possible to suppress sequential scans
	entirely, but turning this variable off discourages the
	planner from using one if there is any other method available.
	The default is on. This is mostly useful to debug the query
	planner.
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       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
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      <term>ENABLE_SORT (<type>boolean</type>)</term>
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      <listitem>
       <para>
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        Enables or disables the query planner's use of explicit sort
	steps. It's not possible to suppress explicit sorts entirely,
	but turning this variable off discourages the planner from
	using one if there is any other method available. The default
	is on. This is mostly useful to debug the query planner.
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       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
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      <term>ENABLE_TIDSCAN (<type>boolean</type>)</term>
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      <listitem>
       <para>
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        Enables or disables the query planner's use of TID scan plan
        types. The default is on. This is mostly useful to debug the
        query planner.
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       </para>
      </listitem>
     </varlistentry>

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     <varlistentry>
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      <term>GEQO (<type>boolean</type>)</term>
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      <listitem>
       <para>
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        Enables or disables genetic query optimization, which is an
        algorithm that attempts to do query planning without
        exhaustive search. This is on by default. See also the various
        other GEQO_ settings.
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       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
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      <term>GEQO_EFFORT (<type>integer</type>)</term>
      <term>GEQO_GENERATIONS (<type>integer</type>)</term>
      <term>GEQO_POOL_SIZE (<type>integer</type>)</term>
      <term>GEQO_RANDOM_SEED (<type>integer</type>)</term>
      <term>GEQO_SELECTION_BIAS (<type>floating point</type>)</term>
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      <listitem>
       <para>
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        Various tuning parameters for the genetic query optimization
        algorithm: The pool size is the number of individuals in one
        population. Valid values are between 128 and 1024. If it is
        set to 0 (the default) a pool size of 2^(QS+1), where QS
642
        is the number of FROM items in the query, is taken. The effort
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        is used to calculate a default for generations. Valid values
        are between 1 and 80, 40 being the default. Generations
        specifies the number of iterations in the algorithm. The
        number must be a positive integer. If 0 is specified then
        Effort * Log2(PoolSize) is used. The run time of the algorithm
        is roughly proportional to the sum of pool size and
        generations. The selection bias is the selective pressure
        within the population. Values can be from 1.50 to 2.00; the
        latter is the default. The random seed can be set to get
        reproduceable results from the algorithm. If it is set to -1
        then the algorithm behaves non-deterministically.
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       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
659
      <term>GEQO_THRESHOLD (<type>integer</type>)</term>
660 661
      <listitem>
       <para>
662 663 664 665
        Use genetic query optimization to plan queries with at least
        this many FROM items involved.  (Note that a JOIN construct
	counts as only one FROM item.) The default is 11. For simpler
	queries it is usually best to use the
666
        deterministic, exhaustive planner.
667 668 669 670 671
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
672
      <term>KSQO (<type>boolean</type>)</term>
673 674
      <listitem>
       <para>
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        The <firstterm>Key Set Query Optimizer</firstterm>
        (<abbrev>KSQO</abbrev>) causes the query planner to convert
        queries whose WHERE clause contains many OR'ed AND clauses
        (such as <literal>WHERE (a=1 AND b=2) OR (a=2 AND b=3)
        ...</literal>) into a UNION query. This method can be faster
        than the default implementation, but it doesn't necessarily
        give exactly the same results, since UNION implicitly adds a
        SELECT DISTINCT clause to eliminate identical output rows.
        KSQO is commonly used when working with products like
        <productname>Microsoft Access</productname>, which tend to
        generate queries of this form.
       </para>

       <para>
        The KSQO algorithm used to be absolutely essential for queries
        with many OR'ed AND clauses, but in
        <productname>Postgres</productname> 7.0 and later the standard
        planner handles these queries fairly successfully. Hence the
        default is OFF.
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       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
699
      <term>RANDOM_PAGE_COST (<type>floating point</type>)</term>
700 701
      <listitem>
       <para>
702 703 704
        Sets the query optimizer's estimate of the cost of a
	nonsequentially fetched disk page. This is measured as a
	multiple of the cost of a sequential page fetch.
705 706 707
       </para>
      </listitem>
     </varlistentry>
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    </variablelist>
   </para>

   <note>
    <para>
     Unfortunately, there is no well-defined method of determining
     ideal values for the family of <quote>COST</quote> variables that
     were just described. You are encouraged to experiment and share
     your findings.
    </para>
   </note>

   </sect2>
721

722 723 724 725 726
   <sect2 id="logging">
    <title>Logging and Debugging</title>

   <para>
    <variablelist>
727 728 729 730 731 732 733
     <varlistentry>
      <term>DEBUG_ASSERTIONS (<type>boolean</type>)</term>
      <listitem>
       <para>
        Turns on various assertion checks. This is a debugging aid. If
        you are experiencing strange problems or crashes you might
        want to turn this on, as it might expose programming mistakes.
734 735 736 737 738
        To use this option, the macro <literal>USE_ASSERT_CHECKING</literal>
        must be defined when Postgres is built (see the configure option
	<literal>--enable-cassert</literal>).  Note that
	<literal>DEBUG_ASSERTIONS</literal> defaults to ON if Postgres
	has been built this way.
739 740 741 742
       </para>
      </listitem>
     </varlistentry>

743
     <varlistentry>
744
      <term>DEBUG_LEVEL (<type>integer</type>)</term>
745 746
      <listitem>
       <para>
747 748 749 750 751
        The higher this value is set, the more
        <quote>debugging</quote> output of various sorts is generated
        in the server log during operation. This option is 0 by
        default, which means no debugging output. Values up to about 4
        currently make sense.
752 753 754
       </para>
      </listitem>
     </varlistentry>
755

756
     <varlistentry>
757 758 759 760 761
      <term>DEBUG_PRINT_PARSE (<type>boolean</type>)</term>
      <term>DEBUG_PRINT_PLAN (<type>boolean</type>)</term>
      <term>DEBUG_PRINT_REWRITTEN (<type>boolean</type>)</term>
      <term>DEBUG_PRINT_QUERY (<type>boolean</type>)</term>
      <term>DEBUG_PRETTY_PRINT (<type>boolean</type>)</term>
762 763
      <listitem>
       <para>
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        For any executed query, prints either the query, the parse
        tree, the execution plan, or the query rewriter output to the
        server log. <option>DEBUG_PRETTY_PRINT</option> selects are
        nicer but longer output format.
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       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
773
      <term>HOSTNAME_LOOKUP (<type>boolean</type>)</term>
774 775
      <listitem>
       <para>
776 777 778 779 780
        By default, connection logs only show the IP address of the
        connecting host. If you want it to show the host name you can
        turn this on, but depending on your host name resolution setup
        it might impose a non-negligible performance penalty. This
        option can only be set at server start.
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       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
786
      <term>LOG_CONNECTIONS (<type>boolean</type>)</term>
787 788
      <listitem>
       <para>
789 790 791 792
        Prints a line informing about each successful connection to
        the server log. This is off by default, although it is
        probably very useful. This option can only be set at server
        start.
793 794 795 796 797
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
798
      <term>LOG_PID (<type>boolean</type>)</term>
799 800
      <listitem>
       <para>
801 802 803
        Prefixes each server log message with the process id of the
        backend process. This is useful to sort out which messages
        pertain to which connection. The default is off.
804 805 806 807 808
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
809
      <term>LOG_TIMESTAMP (<type>boolean</type>)</term>
810 811
      <listitem>
       <para>
812 813
        Prefixes each server log message with a timestamp. The default
        is off.
814 815 816 817 818
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
819 820 821 822
      <term>SHOW_QUERY_STATS (<type>boolean</type>)</term>
      <term>SHOW_PARSER_STATS (<type>boolean</type>)</term>
      <term>SHOW_PLANNER_STATS (<type>boolean</type>)</term>
      <term>SHOW_EXECUTOR_STATS (<type>boolean</type>)</term>
823 824
      <listitem>
       <para>
825 826 827
        For each query, write performance statistics of the respective
        module to the server log. This is a crude profiling
        instrument.
828 829 830 831 832
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
833
      <term>SHOW_SOURCE_PORT (<type>boolean</type>)</term>
834 835
      <listitem>
       <para>
836 837 838 839 840
        Shows the outgoing port number of the connecting host in the
        connection log messages. You could trace back the port number
        to find out what user initiated the connection. Other than
        that it's pretty useless and therefore off by default. This
        option can only be set at server start.
841 842 843 844 845
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
846
      <term>SYSLOG (<type>integer</type>)</term>
847 848
      <listitem>
       <para>
849 850 851 852 853 854 855 856 857 858 859 860
        <productname>Postgres</productname> allows the use of
        <application>syslog</application> for logging. If this option
        is set to 1, messages go both to syslog and the standard
        output. A setting of 2 sends output only to syslog. (Some
        messages will still go to the standard output/error.) The
        default is 0, which means syslog is off. This option must be
        set at server start.
       </para>
       <para>
        To use syslog, the build of
        <productname>Postgres</productname> must be configured with
        the <option>--enable-syslog</option> option.
861 862 863 864
       </para>
      </listitem>
     </varlistentry>

865 866 867 868
     <varlistentry>
      <term>SYSLOG_FACILITY (<type>string</type>)</term>
       <listitem>
        <para>
869 870 871 872 873 874
          This option determines the <application>syslog</application>
          <quote>facility</quote> to be used when syslog is enabled.
          You may choose from LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4,
          LOCAL5, LOCAL6, LOCAL7; the default is LOCAL0.  See also the
          documentation of your system's
          <application>syslog</application>.
875 876 877 878 879
        </para>
       </listitem>
     </varlistentry>
     
     <varlistentry>
880
      <term>SYSLOG_IDENT (<type>string</type>)</term>
881 882
       <listitem>
        <para>
883 884 885 886 887
         If logging to syslog is enabled, this option determines the
         program name used to identify
         <productname>PostgreSQL</productname> messages in
         <application>syslog</application> log messages.  The default
         is <quote>postgres</quote>.
888 889 890 891
        </para>
       </listitem>
      </varlistentry>

892
     <varlistentry>
893
      <term>TRACE_NOTIFY (<type>boolean</type>)</term>
894 895
      <listitem>
       <para>
896 897 898
        Generates a great amount of debugging output for the
        <command>LISTEN</command> and <command>NOTIFY</command>
        commands.
899
       </para>
900 901 902 903 904
      </listitem>
     </varlistentry>
    </variablelist>
   </para>
   </sect2>
905

906 907
   <sect2 id="runtime-config-general">
    <title>General operation</title>
908

909 910 911 912 913 914
   <para>
    <variablelist>
     <varlistentry>
      <term>DEADLOCK_TIMEOUT (<type>integer</type>)</term>
      <listitem>
       <para>
915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930
        This is the amount of time, in milliseconds, to wait on a lock
	before checking to see if there is a deadlock condition or not.
	The check for deadlock is relatively slow, so we don't want to
	run it every time we wait for a lock.  We (optimistically?)
	assume that deadlocks are not common in production applications,
	and just wait on the lock for awhile before starting to ask
	questions about whether it can ever get unlocked.
	Increasing this value reduces the amount of time wasted in
	needless deadlock checks, but slows down reporting of real deadlock
	errors.  The default is 1000 (i.e., one second), which is probably
	about the smallest value you would want in practice.  On a heavily
	loaded server you might want to raise it.  Ideally the setting
	should exceed your typical transaction time, so as to improve the
	odds that the lock will be released before the waiter decides to
	check for deadlock. 
	This option can only be set at server start.
931 932 933 934 935 936 937 938
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>FSYNC (<type>boolean</type>)</term>
      <listitem>
       <para>
939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971
        If this is option is on, the <productname>Postgres</> backend
        will use the <function>fsync()</> system call in several
        places to make sure that updates are physically written to
        disk and will not hang around in the write caches. This
        increases the chance that a database installation will still
        be usable after a operating system or hardware crashes by a
        large amount. (Crashes of the database server itself do
        <emphasis>not</> affect this consideration.)
       </para>

       <para>
        However, this operation severely slows down
        <productname>Postgres</>, because at all those points it has
        to block and wait for the operating system to flush the
        buffers. Without <function>fsync</>, the operating system is
        allowed to do its best in buffering, sorting, and delaying
        writes, so this can be a <emphasis>very</> big perfomance
        increase. However, if the system crashes, parts of the data of
        a transaction that has already been committed -- according to
        the information on disk -- will still hang around in memory.
        Inconsistent data (i.e., data corruption) is therefore likely
        to occur.
       </para>

       <para>
        This option is the subject of an eternal debate in the
        <productname>Postgres</> user and developer communities. Some
        always leave it off, some turn it off only for bulk loads,
        where there is a clear restart point if something goes wrong,
        some leave it on just to be on the safe side. Because it is
        the safe side, on is also the default. If you trust your
        operating system, your utility company, and your hardware, you
        might want to disable it.
972 973 974
       </para>
      </listitem>
     </varlistentry>
975

976 977
     <varlistentry>
      <term>KRB_SERVER_KEYFILE (<type>string</type>)</term>
978 979 980 981 982 983 984 985
      <listitem>
       <para>
        Sets the location of the Kerberos server key file. See
        <xref linkend="kerberos-auth"> for details.
       </para>
      </listitem>
     </varlistentry>

986
     <varlistentry>
987
      <term>MAX_CONNECTIONS (<type>integer</type>)</term>
988 989 990
      <listitem>
       <para>
        Determines how many concurrent connections the database server
991
        will allow. The default is 32. There is also a compiled-in
992 993
        hard upper limit on this value, which is typically 1024
	(both numbers can be altered when compiling the server). This
994
        parameter can only be set at server start.
995 996 997
       </para>
      </listitem>
     </varlistentry>
998

999 1000 1001 1002 1003 1004 1005 1006 1007 1008
     <varlistentry>
      <term>MAX_EXPR_DEPTH (<type>integer</type>)</term>
      <listitem>
       <para>
        Sets the maximum expression nesting depth that the parser will
	accept. The default value is high enough for any normal query,
	but you can raise it if you need to. (But if you raise it too
	high, you run the risk of backend crashes due to stack
	overflow.)
       </para>
1009 1010 1011 1012
      </listitem>
     </varlistentry>

     <varlistentry>
1013
      <term>PORT (<type>integer</type>)</term>
1014 1015
      <listitem>
       <para>
1016 1017
        The TCP port the server listens on; 5432 by default. This
        option can only be set at server start.
1018 1019 1020 1021 1022
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
1023
      <term>SHARED_BUFFERS (<type>integer</type>)</term>
1024 1025
      <listitem>
       <para>
1026 1027 1028
        Sets the number of shared memory buffers the database server
        will use. The default is 64. Each buffer is typically 8192
        bytes. This option can only be set at server start.
1029
       </para>
1030 1031 1032 1033 1034 1035 1036
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>SILENT_MODE (<type>bool</type>)</term>
      <listitem>
       <para>
1037
        Runs postmaster silently. If this option is set, postmaster
1038
        will automatically run in background and any controlling ttys
1039 1040 1041 1042
        are disassociated, thus no messages are written to stdout or
        stderr (same effect as postmaster's -S option). Unless some
        logging system such as syslog is enabled, using this option is
        discouraged since it makes it impossible to see error
1043 1044
        messages.
       </para>
1045 1046 1047
      </listitem>
     </varlistentry>

1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061
     <varlistentry>
      <term>SORT_MEM (<type>integer</type>)</term>
      <listitem>
       <para>
	Specifies the amount of memory to be used by internal sorts
	and hashes before resorting to temporary disk files. The value
	is specified in kilobytes, and defaults to 512 kilobytes. Note
	that for a complex query, several sorts and/or hashes might be
	running in parallel, and each one will be allowed to use as
	much memory as this value specifies before it starts to put
	data into temporary files.
       </para>
      </listitem>
     </varlistentry>
1062 1063 1064 1065 1066 1067 1068 1069

     <varlistentry>
      <term>SQL_INHERITANCE (<type>bool</type>)</term>
      <listitem>
       <para>
        This controls the inheritance semantics, in particular whether
        subtables are included into the consideration of various
        commands by default. This was not the case in versions prior
1070 1071 1072 1073 1074 1075
        to 7.1. If you need the old behaviour you can set this
        variable to off, but in the long run you are encouraged to
        change your applications to use the <literal>ONLY</literal>
        keyword to exclude subtables. See the SQL language reference
        and the <citetitle>User's Guide</citetitle> for more
        information about inheritance.
1076 1077 1078
       </para>
      </listitem>
     </varlistentry>
1079 1080 1081 1082 1083 1084

     <varlistentry>
      <term>SSL (<type>boolean</type>)</term>
      <listitem>
       <para>
        Enables <acronym>SSL</> connections. Please read
1085
        <xref linkend="ssl-tcp"> before using this. The default
1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101
        is off.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>TCPIP_SOCKET (<type>boolean</type>)</term>
      <listitem>
       <para>
        If this is true, then the server will accept TCP/IP
        connections. Otherwise only local Unix domain socket
        connections are accepted. It is off by default. This option
        can only be set at server start.
       </para>
      </listitem>
     </varlistentry>
1102

1103
     <varlistentry>
1104
      <term>UNIX_SOCKET_DIRECTORY (<type>string</type>)</term>
1105 1106
      <listitem>
       <para>
1107
	Specifies the directory of the Unix-domain socket on which the
1108
	<application>postmaster</application> is to listen for
1109 1110
	connections from client applications.  The default is normally
	<filename>/tmp</filename>, but can be changed at build time.
1111 1112 1113 1114
       </para>
      </listitem>
     </varlistentry>

1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164
     <varlistentry>
      <term>UNIX_SOCKET_GROUP (<type>string</type>)</term>
      <listitem>
       <para>
        Sets the group owner of the Unix domain socket.  (The owning
        user of the socket is always the user that starts the
        postmaster.)  In combination with the option
        <option>UNIX_SOCKET_PERMISSIONS</option> this can be used as
        an additional access control mechanism for this socket type.
        By default this is the empty string, which uses the default
        group for the current user.  This option can only be set at
        server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>UNIX_SOCKET_PERMISSIONS (<type>integer</type>)</term>
      <listitem>
       <para>
        Sets the access permissions of the Unix domain socket.  Unix
        domain sockets use the usual Unix file system permission set.
        The option value is expected to be an numeric mode
        specification in the form accepted by the
        <function>chmod</function> and <function>umask</function>
        system calls.  (To use the customary octal format the number
        must start with a <literal>0</literal> (zero).)
       </para>

       <para>
        The default permissions are <literal>0777</literal>, meaning
        anyone can connect.  Reasonable alternatives would be
        <literal>0770</literal> (only user and group, see also under
        <option>UNIX_SOCKET_GROUP</option>) and
        <literal>0700</literal> (only user).  (Note that actually for
        a Unix socket, only write permission matters and there is no
        point in setting or revoking read or execute permissions.)
       </para>

       <para>
        This access control mechanism is independent from the one
        described in <xref linkend="client-authentication">.
       </para>

       <para>
        This option can only be set at server start.
       </para>
      </listitem>
     </varlistentry>

1165 1166 1167 1168 1169 1170
     <varlistentry>
      <term>VIRTUAL_HOST (<type>string</type>)</term>
      <listitem>
       <para>
	Specifies the TCP/IP hostname or address on which the
	<application>postmaster</application> is to listen for
1171 1172
	connections from client applications.  Defaults to
	listening on all configured addresses (including localhost).
1173 1174 1175 1176
       </para>
      </listitem>
     </varlistentry>

1177
    </variablelist>
1178
   </para>
1179
   </sect2>
1180

1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231
   <sect2 id="runtime-config-wal">
    <title>WAL</title>

   <para>
    See also <xref linkend="wal-configuration"> for details on WAL
    tuning.

    <variablelist>
     <varlistentry>
      <term>CHECKPOINT_TIMEOUT (<type>integer</type>)</term>
      <listitem>
       <para>
        Frequency of automatic WAL checkpoints, in seconds.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>WAL_BUFFERS (<type>integer</type>)</term>
      <listitem>
       <para>
        Number of buffers for WAL.  This option can only be set at
        server start.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>WAL_DEBUG (<type>integer</type>)</term>
      <listitem>
       <para>
        If non-zero, turn on WAL-related debugging output on standard
        error.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>WAL_FILES (<type>integer</type>)</term>
      <listitem>
       <para>
        Number of log files that are created in advance at checkpoint
        time.  This option can only be set at server start.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
    </para>
   </sect2>


1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252
   <sect2 id="runtime-config-short">
    <title>Short options</title>
   <para>
    For convenience there are also single letter option switches
    available for many parameters. They are described in the following
    table.

    <table>
     <title>Short option key</title>
     <tgroup cols="3">
      <colspec colnum="3" align="center">
      <thead>
       <row>
        <entry>Short option</entry>
        <entry>Equivalent</entry>
        <entry>Remark</entry>
       </row>
      </thead>
      <tbody>
       <row>
        <entry>-B <replaceable>x</replaceable></entry>
1253
        <entry>shared_buffers = <replaceable>x</replaceable></entry>
1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265
        <entry></entry>
       </row>
       <row>
        <entry>-d <replaceable>x</replaceable></entry>
        <entry>debug_level = <replaceable>x</replaceable></entry>
        <entry></entry>
       </row>
       <row>
        <entry>-F</entry>
        <entry>fsync = off</entry>
        <entry></entry>
       </row>
1266 1267 1268 1269 1270
       <row>
        <entry>-h <replaceable>x</replaceable></entry>
        <entry>virtual_host = <replaceable>x</replaceable></entry>
        <entry></entry>
       </row>
1271 1272
       <row>
        <entry>-i</entry>
1273
        <entry>tcpip_socket = on</entry>
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        <entry></entry>
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       </row>
       <row>
        <entry>-k <replaceable>x</replaceable></entry>
        <entry>unix_socket_directory = <replaceable>x</replaceable></entry>
        <entry></entry>
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       </row>
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       <row>
        <entry>-l</entry>
        <entry>ssl = on</entry>
        <entry></entry>
       </row>
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       <row>
        <entry>-N <replaceable>x</replaceable></entry>
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        <entry>max_connections = <replaceable>x</replaceable></entry>
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        <entry></entry>
       </row>
       <row>
        <entry>-p <replaceable>x</replaceable></entry>
        <entry>port = <replaceable>x</replaceable></entry>
        <entry></entry>
       </row>

       <row>
        <entry>-fi, -fh, -fm, -fn, -fs, -ft</entry>
        <entry>enable_indexscan=off, enable_hashjoin=off,
        enable_mergejoin=off, enable_nestloop=off, enable_seqscan=off,
        enable_tidscan=off</entry>
        <entry>*</entry>
       </row>
       <row>
        <entry>-S <replaceable>x</replaceable></entry>
        <entry>sort_mem = <replaceable>x</replaceable></entry>
        <entry>*</entry>
       </row>
       <row>
        <entry>-s</entry>
        <entry>show_query_stats = on</entry>
        <entry>*</entry>
       </row>
       <row>
        <entry>-tpa, -tpl, -te</entry>
        <entry>show_parser_stats=on, show_planner_stats=on, show_executor_stats=on</entry>
        <entry>*</entry>
       </row>
      </tbody>
     </tgroup>
    </table>
    For historical reasons, options marked <quote>*</quote> must be
    passed to the individual backend process via the
    <option>-o</option> postmaster option, for example,
<screen>
&gt; <userinput>postmaster -o '-S 1024 -s'</userinput>
</screen>
    or via <envar>PGOPTIONS</envar> from the client side, as explained
    above.
   </para>

   </sect2>
 </sect1>

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 <sect1 id="kernel-resources">
  <title>Managing Kernel Resources</title>

  <para>
   A large <productname>Postgres</> installation can quickly hit
   various operating system resource limits. (On some systems, the
   factory defaults are so low that you don't even need a really
   <quote>large</> installation.) If you have encountered this kind of
   problem then keep reading.
  </para>

  <sect2 id="sysvipc">
   <title>Shared Memory and Semaphores</title>

   <para>
    Shared memory and semaphores are collectively referred to as
    <quote>System V IPC</> (together with message queues, which are
    not relevant for <productname>Postgres</>). Almost all modern
    operating systems provide these features, but not all of them have
    them turned on or sufficiently sized by default, especially
    systems with BSD heritage. (For the QNX port,
    <productname>Postgres</> provides its own replacement
    implementation of these facilities.)
   </para>

   <para>
    The complete lack of these facilities is usually manifested by an
    <errorname>Illegal system call</> error upon postmaster start. In
    that case there's nothing left to do but to reconfigure your
    kernel -- <productname>Postgres</> won't work without them.
   </para>

   <para>
    When <productname>Postgres</> exceeds one of the various hard
    limits of the IPC resources then the postmaster will refuse to
    start up and should leave a marginally instructive error message
    about which problem was encountered and what needs to be done
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    about it.  (See also <xref linkend="postmaster-start-failures">.)
    The relevant kernel parameters are named
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    consistently across different systems; <xref
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    linkend="sysvipc-parameters"> gives an overview. The methods to
    set them, however, vary; suggestions for some platforms are given
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    below. Be warned that it is often necessary to reboot your
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    machine at least, possibly even recompile the kernel, to change these
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    settings.
   </para>


   <table id="sysvipc-parameters">
    <title>System V IPC parameters</>

    <tgroup cols="3">
     <thead>
      <row>
       <entry>Name</>
       <entry>Description</>
       <entry>Reasonable values</>
      </row>
     </thead>

     <tbody>
      <row>
       <entry><varname>SHMMAX</></>
       <entry>Maximum size of shared memory segment (bytes)</>
       <entry>512 kB + 8192 * buffers + extra ... infinity</entry>
      </row>

      <row>
       <entry><varname>SHMMIN</></>
       <entry>Minimum size of shared memory segment (bytes)</>
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       <entry>1 (at most about 256 kB)</>
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      </row>

      <row>
       <entry><varname>SHMSEG</></>
       <entry>Maximum number of shared memory segments per process</>
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       <entry>only 1 segment is needed, but the default is much higher</>
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      </row>

       <row>
        <entry><varname>SHMMNI</></>
        <entry>Maximum number of shared memory segments system-wide</>
        <entry>like <varname>SHMSEG</> + room for other applications</>
       </row>

       <row>
        <entry><varname>SEMMNI</></>
        <entry>Maximum number of semaphore identifiers (i.e., sets)</>
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        <entry>&gt;= ceil(max_connections / 16)</>
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       </row>

       <row>
        <entry><varname>SEMMNS</></>
        <entry>Maximum number of semaphores system-wide</>
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        <entry>ceil(max_connections / 16) * 17 + room for other applications</>
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       </row>

       <row>
        <entry><varname>SEMMSL</></>
        <entry>Maximum number of semaphores per set</>
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        <entry>&gt;= 17</>
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       </row>

       <row>
        <entry><varname>SEMMAP</></>
        <entry>Number of entries in semaphore map</>
        <entry>see text</>
       </row>

       <row>
        <entry><varname>SEMVMX</></>
        <entry>Maximum value of semaphore</>
        <entry>&gt;= 255  (The default is often 32767, don't change unless asked to.)</>
       </row>

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


   <para>
    The most important shared memory parameter is <varname>SHMMAX</>,
    the maximum size, in bytes, that a shared memory segment can have.
    If you get an error message from <function>shmget</> along the
    lines of <errorname>Invalid argument</> then it is possible that
    this limit has been exceeded. The size of the required shared
    memory segments varies both with the number of requested buffers
    (<option>-B</> option) and the number of allowed connections
    (<option>-N</> option), although the former is the dominant item.
    (You can therefore, as a temporary solution, lower these settings
    to get rid of the failures.) As a rough approximation you can
    estimate the required segment size as the number of buffers times
    the block size (8192 kB by default) plus ample overhead (at least
    half a megabyte). Any error message you might get will contain the
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    size of the failed allocation.
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   </para>

   <para>
    Less likely to cause problems is the minimum size for shared
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    memory segments (<varname>SHMMIN</>), which should be at most
    somewhere around 256 kB for <productname>Postgres</> (it is
    usually just 1). The maximum number of segments system-wide
    (<varname>SHMMNI</>) or per-process (<varname>SHMSEG</>) should
    not cause a problem unless your system has them set to zero. Some
    systems also have a limit on the total amount of shared memory in
    the system; see the platform-specific instructions below.
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   </para>

   <para>
    <productname>Postgres</> uses one semaphore per allowed connection
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    (<option>-N</> option), in sets of 16.  Each such set will also
    contain a 17th semaphore which contains a <quote>magic
    number</quote>, to avoid collision with semaphore sets used by
    other applications. The maximum number of semaphores in the system
    is set by <varname>SEMMNS</>, which consequently must be at least
    as high as the connection setting plus one extra for each 16
    allowed connections (see the formula in <xref
    linkend="sysvipc-parameters">.  The parameter <varname>SEMMNI</>
    determines the limit on the number of semaphore sets that can
    exist on the system at one time.  Hence this parameter must be at
    least <literal>ceil(max_connections / 16)</>. Lowering the number
    of allowed connections is a temporary workaround for failures,
    which are usually confusingly worded <quote><errorname>No space
    left on device</></>, from the function <function>semget()</>.
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   </para>

   <para>
    In some cases it might also turn out to be necessary to increase
    <varname>SEMMAP</> to be at least on the order of
    <varname>SEMMNS</>. This parameter defines the size of the
    semaphore resource map, in which each contiguous block of available
    semaphores needs an entry. When a semaphore set is freed it is
    either added to an existing entry that is adjacent to the freed
    block or it is registered under a new map entry. If the map is
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    full, the freed semaphores get lost (until reboot). Fragmentation
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    of the semaphore space could therefore over time lead to less
    available semaphores than there should be.
   </para>

   <para>
    The <varname>SEMMSL</> parameter, which determines how many
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    semaphores can be in a set, must be at least 17 for
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    <productname>Postgres</>.
   </para>

   <para>
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    Various other settings related to <quote>semaphore undo</>, such as
    <varname>SEMMNU</> and <varname>SEMUME</>, are not of concern
    for <productname>Postgres</>.
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   </para>


   <para>
    <variablelist>

     <varlistentry>
      <term>BSD/OS</>
      <listitem>
       <formalpara>
        <title>Shared Memory</>
        <para>
         By default, only 4 MB of shared memory is supported. Keep in
         mind that shared memory is not pageable; it is locked in RAM.
         To increase the number of buffers supported by the
         postmaster, increase <varname>SHMMAXPGS</> by 1024 for every
         additional 4 MB of shared memory:
<programlisting>
/sys/sys/shm.h:69:#define       SHMMAXPGS       1024    /* max hardware pages... */
</programlisting>
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         The default setting of 1024 provides a maximum of 4 MB of shared
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         memory.
        </para>
       </formalpara>

       <para>
        For those running 4.1 or later, just recompile the kernel and
        reboot. For those running earlier releases, use
        <application>bpatch</> to find the <varname>sysptsize</> value
        for the current kernel. This is computed dynamically at
        bootup.
<screen>
$ <userinput>bpatch -r sysptsize</>
<computeroutput>0x9 = 9</>
</screen>
        Next, change <varname>SYSPTSIZE</> to a hard-coded value. Use
        the bpatch value, plus add 1 for every additional 4 MB of
        shared memory you desire.
<programlisting>
/sys/i386/i386/i386_param.c:28:#define  SYSPTSIZE 0        /* dynamically... */
</programlisting>
        <varname>sysptsize</> can not be changed by sysctl on the fly.
       </para>

       <formalpara>
        <title>Semaphores</>
        <para>
         You may need to increase the number of semaphores. By
         default, <productname>Postgres</> allocates 32 semaphores,
         one for each backend connection. This is just over half the
         default system total of 60.
        </para>
       </formalpara>

       <para>
        The defaults are in <filename>/sys/sys/sem.h</>:
<programlisting>
/* Configuration parameters */
#ifndef SEMMNI
#define SEMMNI  10              /* # of semaphore identifiers */
#endif
#ifndef SEMMNS
#define SEMMNS  60              /* # of semaphores in system */
#endif
#ifndef SEMUME
#define SEMUME  10              /* max # of undo entries per process */
#endif
#ifndef SEMMNU
#define SEMMNU  30              /* # of undo structures in system */
#endif
</programlisting>
        Set the values you want in your kernel config file, e.g.:
<programlisting>
options "SEMMNI=40"
options "SEMMNS=240"
options "SEMUME=40"
options "SEMMNU=120"
</programlisting>
       </para>
      </listitem>
     </varlistentry>


     <varlistentry>
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      <term>FreeBSD</term>
      <term>OpenBSD</term>
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      <listitem>
       <para>
        The options <varname>SYSVSHM</> and <varname>SYSVSEM</> need
        to be enabled when the kernel is compiled. (They are by
        default.) The maximum size of shared memory is determined by
        the option <varname>SHMMAXPGS</> (in pages). The following
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        shows an example of how to set the various parameters:
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<programlisting>
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options         SYSVSHM
options         SHMMAXPGS=4096
options         SHMSEG=256

options         SYSVSEM
options         SEMMNI=256
options         SEMMNS=512
options         SEMMNU=256
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options         SEMMAP=256
</programlisting>
       </para>
      </listitem>
     </varlistentry>


     <varlistentry>
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      <term>HP-UX</>
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      <listitem>
       <para>
        The default settings tend to suffice for normal installations.
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        On <productname>HP-UX</> 10, the factory default for
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        <varname>SEMMNS</> is 128, which might be too low for larger
        database sites.
       </para>
       <para>
        IPC parameters can be set in the <application>System
        Administration Manager</> (<acronym>SAM</>) under
        <menuchoice><guimenu>Kernel
        Configuration</><guimenuitem>Configurable Parameters</></>.
        Hit <guibutton>Create A New Kernel</> when you're done.
       </para>
      </listitem>
     </varlistentry>


     <varlistentry>
      <term>Linux</>
      <listitem>
       <para>
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        The default shared memory limit (both
        <varname>SHMMAX</varname> and <varname>SHMALL</varname>) is 32
        MB in 2.2 kernels, but it can be changed in the
        <filename>proc</filename> file system (without reboot).  For
        example, to allow 128 MB:
<screen>
<prompt>$</prompt> <userinput>echo 134217728 >/proc/sys/kernel/shmall</userinput>
<prompt>$</prompt> <userinput>echo 134217728 >/proc/sys/kernel/shmmax</userinput>
</screen>
        You could put these commands into a script run at boot-time.
       </para>

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       <para>
        Alternatively, you can use
        <citerefentry><refentrytitle>sysctl</refentrytitle>
        <manvolnum>8</manvolnum></citerefentry>, if available, to
        control these parameters.  Look for a file called
        <filename>/etc/sysctl.conf</filename> and add lines like the
        following to it:
<programlisting>
kernel.shmall = 134217728
kernel.shmmax = 134217728
</programlisting>
        This file is usually processed at boot time, but
        <application>sysctl</application> can also be called
        explicitly later.
       </para>

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       <para>
        Other parameters are sufficiently sized for any application.
        If you want to see for yourself look into
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        <filename>/usr/src/linux/include/asm-<replaceable>xxx</>/shmparam.h</>
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        and <filename>/usr/src/linux/include/linux/sem.h</>.
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       </para>
      </listitem>
     </varlistentry>


     <varlistentry>
      <term>SCO OpenServer</>
      <listitem>
       <para>
        In the default configuration, only 512 kB of shared memory per
        segment is allowed, which is about enough for <option>-B 24 -N
        12</>. To increase the setting, first change the directory to
        <filename>/etc/conf/cf.d</>. To display the current value of
        <varname>SHMMAX</>, in bytes, run
<programlisting>
./configure -y SHMMAX
</programlisting>
        To set a new value for <varname>SHMMAX</>, run:
<programlisting>
./configure SHMMAX=<replaceable>value</>
</programlisting>
        where <replaceable>value</> is the new value you want to use
        (in bytes). After setting <varname>SHMMAX</>, rebuild the kernel
<programlisting>
./link_unix
</programlisting>
        and reboot.
       </para>
      </listitem>
     </varlistentry>


     <varlistentry>
      <term>Solaris</>
      <listitem>
       <para>
        At least in version 2.6, the maximum size of a shared memory
        segment is set too low for <productname>Postgres</>. The
        relevant settings can be changed in <filename>/etc/system</>,
        for example:
<programlisting>
set shmsys:shminfo_shmmax=0x2000000
set shmsys:shminfo_shmmin=1
set shmsys:shminfo_shmmni=256
set shmsys:shminfo_shmseg=256

set semsys:seminfo_semmap=256
set semsys:seminfo_semmni=512
set semsys:seminfo_semmns=512
set semsys:seminfo_semmsl=32
</programlisting>
        You need to reboot to make the changes effective.
       </para>

       <para>
        See also <ulink
        url="http://www.sunworld.com/swol-09-1997/swol-09-insidesolaris.html">http://www.sunworld.com/swol-09-1997/swol-09-insidesolaris.html</>
        for information on shared memory under
        <productname>Solaris</>.
       </para>
      </listitem>
     </varlistentry>


     <varlistentry>
      <term>UnixWare</>
      <listitem>
       <para>
        On <productname>UnixWare</> 7, the maximum size for shared
        memory segments is 512 kB in the default configuration. This
        is enough for about <option>-B 24 -N 12</>. To display the
        current value of <varname>SHMMAX</>, run
<programlisting>
/etc/conf/bin/idtune -g SHMMAX
</programlisting>
        which displays the current, default, minimum, and maximum
        values, in bytes. To set a new value for <varname>SHMMAX</>,
        run:
<programlisting>
/etc/conf/bin/idtune SHMMAX <replaceable>value</>
</programlisting>
        where <replaceable>value</> is the new value you want to use
        (in bytes). After setting <varname>SHMMAX</>, rebuild the
        kernel
<programlisting>
/etc/conf/bin/idbuild -B
</programlisting>
        and reboot.
       </para>
      </listitem>
     </varlistentry>

    </variablelist>

   </para>
  </sect2>

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  <sect2>
   <title>Resource Limits</title>

   <para>
    Unix-like operating systems enforce various kinds of resource
    limits that might interfere with the operation of your
    <productname>Postgres</productname> server.  Of importance are
    especially the limits on the number of processes per user, the
    number of open files per process, and the amount of memory
    available to a process.  Each of these have a <quote>hard</quote>
    and a <quote>soft</quote> limit.  The soft limit is what actually
    counts but it can be changed by the user up to the hard limit.
    The hard limit can only be changed by the root user.  The system
    call <function>setrlimit</function> is responsible for setting
    these parameters.  The shell the built-in command
    <command>ulimit</command> (Bourne shells) or
    <command>limit</command> (csh) is used to control the resource
    limits from the command line.  On BSD-derived systems the file
    <filename>/etc/login.conf</filename> controls what values the
    various resource limits are set to upon login.  See
    <citerefentry><refentrytitle>login.conf</refentrytitle>
    <manvolnum>5</manvolnum></citerefentry> for details.  The relevant
    parameters are <varname>maxproc</varname>,
    <varname>openfiles</varname>, and <varname>datasize</varname>.
    For example:
<programlisting>
default:\
...
        :datasize-cur=256M:\
        :maxproc-cur=256:\
        :openfiles-cur=256:\
...
</programlisting>
    (<literal>-cur</literal> is the soft limit.  Append
    <literal>-max</literal> to set the hard limit.)
   </para>

   <para>
    Kernels generally also have an implementation-dependent
    system-wide limit on some resources.
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    <itemizedlist>
     <listitem>
      <para>
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      On <productname>Linux</productname>
      <filename>/proc/sys/fs/file-max</filename> determines the
      maximum number of files that the kernel will allocate.  It can
      be changed by writing a different number into the file or by
      adding an assignment in <filename>/etc/sysctl.conf</filename>.
      The maximum limit of files per process is fixed at the time the
      kernel is compiled; see
      <filename>/usr/src/linux/Documentation/proc.txt</filename> for
      more information.
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      </para>
     </listitem>
    </itemizedlist>
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   </para>

   <para>
    The <productname>Postgres</productname> server uses one process
    per connection so you should provide for at least as many processes
    as allowed connections, in addition to what you need for the rest
    of your system.  This is usually not a problem but if you run
    several servers on one machine things might get tight.
   </para>

   <para>
    The factory default limit on open files is often set to
    <quote>socially friendly</quote> values that allow many users to
    coexist on a machine without using an inappropriate fraction of
    the system resources.  If you run many servers on a machine this
    is perhaps what you want, but on dedicated servers you may want to
    raise this limit.
   </para>
  </sect2>
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 </sect1>


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 <sect1 id="postmaster-shutdown">
  <title>Shutting down the server</title>

  <para>
   Depending on your needs, there are several ways to shut down the
   database server when your work is done. The differentiation is
   done by what signal you send to the server process.
   <variablelist>
    <varlistentry>
     <term>SIGTERM</term>
     <listitem>
      <para>
       After receiving SIGTERM, the postmaster disallows new
       connections but lets active backend end their work and shuts
       down only after all of them terminated (by client request).
       This is the <firstterm>Smart Shutdown</firstterm>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>SIGINT</term>
     <listitem>
      <para>
       The postmaster disallows new connections, sends all active
       backends SIGTERM (which will cause them to abort immediately),
       waits for children to exit and shuts down the data base. This
       is the <firstterm>Fast Shutdown</firstterm>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term>SIGQUIT</term>
     <listitem>
      <para>
       This is the <firstterm>Immediate Shutdown</firstterm> which
       will cause the postmaster to send a SIGUSR1 to all backends and
       exit immediately (without properly shutting down the database
       system). When WAL is implemented, this will lead to recovery on
1907
       start-up. Right now it's not recommendable to use this option.
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      </para>
     </listitem>
    </varlistentry>
   </variablelist>

   <caution>
    <para>
     If at all possible, do not use SIGKILL to shut down the
     postmaster. This can cause data corruption and will prevent the
     cleaning up of shared memory resources, which you will have to
     do yourself in that case.
    </para>
   </caution>

   The PID of the postmaster process can be found using the
   <application>ps</application> program, or from the file
   <filename>postmaster.pid</filename> in the data directory. So for
   example, to do a fast shutdown:
<screen>
&gt; <userinput>kill -INT `cat /usr/local/pgsql/data/postmaster.pid`</userinput>
</screen>
  </para>
  <para>
   The program <application>pg_ctl</application> is a shell script
   wrapper that provides a convenient interface to these functions.
  </para>
 </sect1>

1936
 <sect1 id="ssl-tcp">
1937
  <title>Secure TCP/IP Connections with SSL</title>
1938 1939

  <para>
1940 1941
   <productname>PostgreSQL</> has native support for connections over
   <acronym>SSL</> to encrypt
1942 1943
   client/server communications for increased security. This requires
   <productname>OpenSSL</productname> to be installed on both client
1944 1945
   and server systems and support enabled at build-time (see <xref
   linkend="installation">).
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  </para>

  <para>
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   With SSL support compiled in, the <productname>PostgreSQL</> server
   can be started with the argument <option>-l</> (ell) to enable
   SSL connections. When starting in SSL mode, the postmaster will look
   for the files <filename>server.key</> and <filename>server.crt</> in
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   the data directory.  These files should contain the server private key
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   and certificate respectively. These files must be set up correctly
   before an SSL-enabled server can start. If the private key is protected
   with a passphrase, the postmaster will prompt for the passphrase and will
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   not start until it has been entered.
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  </para>

  <para>
   The postmaster will listen for both standard and SSL connections
   on the same TCP/IP port, and will negotiate with any connecting
1963
   client whether or not to use SSL.
1964
   See <xref linkend="client-authentication">
1965 1966
   about how to force on the server side the use of SSL for certain
   connections.
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  </para>

  <para>
   For details on how to create your server private key and certificate,
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   refer to the <productname>OpenSSL</> documentation. A simple self-signed
1972
   certificate can be used to get started for testing, but a certificate signed
1973
   by a CA (either one of the global CAs or a local one) should be used in 
1974
   production so the client can verify the servers identity. To create
1975
   a quick self-signed certificate, use the following OpenSSL command:
1976 1977 1978
<programlisting>
openssl req -new -text -out cert.req
</programlisting>
1979 1980
   Fill out the information that openssl asks for. Make sure that you enter
   the local host name as Common Name; the challenge password can be
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   left blank. The script will generate a key that is passphrase protected;
   it will not accept a pass phrase that is less than four characters long.
   To remove the passphrase (as you must if you want automatic start-up of
   the postmaster), run the commands
<programlisting>
1986
openssl rsa -in privkey.pem -out cert.pem
1987
</programlisting>
1988
   Enter the old passphrase to unlock the existing key. Now do
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<programlisting>
openssl req -x509 -in cert.req -text -key cert.pem -out cert.cert
cp cert.pem <replaceable>$PGDATA</replaceable>/server.key
cp cert.cert <replaceable>$PGDATA</replaceable>/server.crt
</programlisting>
1994
   to turn the certificate into a self-signed certificate and to copy the
1995
   key and certificate to where the postmaster will look for them.
1996 1997 1998
  </para>
 </sect1>

1999
 <sect1 id="ssh-tunnels">
2000
  <title>Secure TCP/IP Connections with SSH tunnels</title>
2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044

  <note>
   <title>Acknowledgement</title>
   <para>
    Idea taken from an email by Gene Selkov, Jr.
    (<email>selkovjr@mcs.anl.gov</>) written on 1999-09-08 in response
    to a question from Eric Marsden.
   </para>
  </note>

  <para>
   One can use <productname>ssh</productname> to encrypt the network
   connection between clients and a
   <productname>Postgres</productname> server. Done properly, this
   should lead to an adequately secure network connection.
  </para>

  <para>
   First make sure that an <productname>ssh</productname> server is
   running properly on the same machine as
   <productname>Postgres</productname> and that you can log in using
   ssh as some user. Then you can establish a secure tunnel with a
   command like this from the client machine:
<programlisting>
&gt; <userinput>ssh -L 3333:foo.com:5432 joe@foo.com</userinput>
</programlisting>
   The first number in the <option>-L</option> argument, 3333, is the
   port number of your end of the tunnel; it can be chosen freely. The
   second number, 5432, is the remote end of the tunnel -- the port
   number your backend is using. The name or the address in between
   the port numbers is the host with the database server you are going
   to connect to. In order to connect to the database server using
   this tunnel, you connect to port 3333 on the local machine:
<programlisting>
psql -h localhost -p 3333 template1
</programlisting>
   To the database server it will then look as though you are really
   user <literal>joe@foo.com</literal> and it will use whatever
   authentication procedure was set up for this user. In order for the
   tunnel setup to succeed you must be allowed to connect via ssh as
   joe@foo.com, just as if you had attempted to use ssh to set up a
   terminal session.
  </para>

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  <tip>
   <para>
    Several other products exist that can provide secure tunnels using
    a procedure similar in concept to the one just described.
   </para>
  </tip>

2052
 </sect1>
2053 2054

</Chapter>
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