<!-- doc/src/sgml/release-9.6.sgml -->
<!-- See header comment in release.sgml about typical markup -->

 <sect1 id="release-9-6">
  <title>Release 9.6</title>

  <note>
   <title>Release Date</title>
   <simpara>2016-??-??</simpara>
   <simpara>Current as of 2016-08-08 (commit 34927b292)</simpara>
  </note>

  <sect2>
   <title>Overview</title>

   <para>
    Major enhancements in <productname>PostgreSQL</> 9.6 include:
   </para>

   <!-- Items in this list summarize one or more items below -->

   <itemizedlist>

    <listitem>
     <para>
      Parallel sequential scans, joins and aggregates
     </para>
    </listitem>

    <listitem>
     <para>
      Eliminate repetitive scanning of old data by autovacuum
     </para>
    </listitem>

    <listitem>
     <para>
      Synchronous replication now allows multiple standby servers, for
      increased reliability
     </para>
    </listitem>

    <listitem>
     <para>
      Allow full-text search for phrases (multiple adjacent words)
     </para>
    </listitem>

    <listitem>
     <para>
      Support foreign/remote joins, sorts, and <command>UPDATE</>s in
      <filename>postgres_fdw</>
     </para>
    </listitem>

    <listitem>
     <para>
      Substantial performance improvements, especially in the area of
      scalability on multi-<literal>CPU</>-socket servers
     </para>
    </listitem>

   </itemizedlist>

   <para>
    The above items are explained in more detail in the sections below.
   </para>

  </sect2>

  <sect2>

  <title>Migration to Version 9.6</title>

   <para>
    A dump/restore using <xref linkend="app-pg-dumpall">, or use of <xref
    linkend="pgupgrade">, is required for those wishing to migrate data
    from any previous release.
   </para>

   <para>
    Version 9.6 contains a number of changes that may affect compatibility
    with previous releases.  Observe the following incompatibilities:
   </para>

   <itemizedlist>

      <listitem>
<!--
2016-08-07 [d8710f18f] Correct column name in information schema
-->
       <para>
        Change the column name in the
        <structname>information_schema</>.<structname>routines</>
        view from <structfield>result_cast_character_set_name</>
        to <structfield>result_cast_char_set_name</> (Cl&eacute;ment
        Pr&eacute;vost)
       </para>

       <para>
        The SQL:2011 standard specifies the longer name, but that appears
        to be a mistake, because adjacent column names use the shorter
        style, as do other <structname>information_schema</> views.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-10 [53be0b1ad] Provide much better wait information in pg_stat_activity
-->
       <para>
        Improve the <link
        linkend="pg-stat-activity-view"><structname>pg_stat_activity</></link>
        view's information about what a process is waiting for (Amit
        Kapila, Ildus Kurbangaliev)
       </para>

       <para>
        Historically a process has only been shown as waiting if it was
        waiting for a heavy weight lock.  Now waits for light weight locks
        and buffer pins are also shown in <structname>pg_stat_activity</>.
        Also, the type of lock being waited for is now visible.
        These changes replace the <structfield>waiting</> column with
        <structfield>wait_event_type</> and <structfield>wait_event</>.
       </para>
      </listitem>

      <listitem>
<!--
2015-10-05 [2d87eedc1] to_char(): Do not count negative sign as a digit for tim
-->
       <para>
        In <link
        linkend="functions-formatting-table"><function>to_char()</></>,
        do not count a minus sign (when needed) as part of the field
        width for time-related fields (Bruce Momjian)
       </para>

       <para>
        For example, <literal>to_char('-4 years'::interval, 'YY')</>
        now returns <literal>-04</>, rather than <literal>-4</>.
       </para>
      </listitem>

      <listitem>
<!--
2016-01-21 [647d87c56] Make extract() do something more reasonable with infinit
-->
       <para>
        Make <link
        linkend="functions-datetime-table"><function>extract()</></> behave
        more reasonably with <literal>infinite</> inputs (Vitaly Burovoy)
       </para>

       <para>
        Historically the <function>extract()</> function just returned
        zero given an infinite timestamp, regardless of the given
        unit name.  Make it return <literal>infinity</literal>
        or <literal>-infinity</literal> as appropriate when the
        requested field is one that is monotonically increasing (e.g,
        <literal>year</>, <literal>epoch</>), or <literal>NULL</> when
        it is not (e.g., <literal>day</>, <literal>hour</>).  Also,
        throw the expected error for bad unit names.
       </para>
      </listitem>

      <listitem>
<!--
2015-09-05 [0426f349e] Rearrange the handling of error context reports.
This commit is also listed under libpq and psql
-->
       <para>
        Remove PL/pgSQL's <quote>feature</> that suppressed the
        innermost line of <literal>CONTEXT</> for messages emitted by
        <command>RAISE</> commands (Pavel Stehule)
       </para>

       <para>
        This ancient backwards-compatibility hack was agreed to have
        outlived its usefulness.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-29 [61d66c44f] Fix support of digits in email/hostnames.
-->
       <para>
        Fix text search parser to allow leading digits in <literal>email</>
        and <literal>host</> tokens (Artur Zakirov)
       </para>

       <para>
        In most cases this will result in few changes in the parsing of
        text.  But if you have data where such addresses occur frequently,
        it may be worth rebuilding dependent <type>tsvector</> columns
        and indexes so that addresses of this form will be found properly
        by text searches.
       </para>
      </listitem>

      <listitem>
<!--
2015-09-04 [1bbd52cb9] Make unaccent handle all diacritics known to Unicode, an
2016-03-16 [9a206d063] Improve script generating unaccent rules
-->
       <para>
        Extend <filename>contrib/unaccent</>'s standard
        <filename>unaccent.rules</> file to handle all diacritics
        known to Unicode, and expand ligatures correctly (Thomas Munro,
        L&eacute;onard Benedetti)
       </para>

       <para>
        The previous version omitted some less-common letters with
        diacritic marks.  It now also expands ligatures into separate
        letters.  Installations that use this rules file may wish to
        rebuild <type>tsvector</> columns and indexes that depend on
        the result.
       </para>
      </listitem>

      <listitem>
<!--
2015-10-22 [d371bebd3] Remove redundant CREATEUSER/NOCREATEUSER options in CREA
-->
       <para>
        Remove the long-deprecated
        <literal>CREATEUSER</>/<literal>NOCREATEUSER</> options from
        <command>CREATE ROLE</> and allied commands (Tom Lane)
       </para>

       <para>
        <literal>CREATEUSER</> actually meant <literal>SUPERUSER</>,
        for ancient backwards-compatibility reasons.  This has been a
        constant source of confusion for people who (reasonably) expect
        it to mean <literal>CREATEROLE</>.  It has been deprecated for
        ten years now, so fix the problem by removing it.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-08 [293007898] Reserve the "pg_" namespace for roles
2016-05-06 [a89505fd2] Remove various special checks around default roles
2016-05-08 [7df974ee0] Disallow superuser names starting with 'pg_' in initdb
-->
       <para>
        Treat role names beginning with <literal>pg_</> as reserved
        (Stephen Frost)
       </para>

       <para>
        User creation of such role names is now disallowed.  This prevents
        conflicts with built-in roles created by <application>initdb</>.
       </para>
      </listitem>

      <listitem>
<!--
2015-12-08 [d5563d7df] psql: Support multiple -c and -f options, and allow mixi
-->
       <para>
        Support multiple <option>-c</option> and <option>-f</option>
        command-line options (Pavel Stehule, Catalin Iacob)
       </para>

       <para>
        To allow this with sane behavior, one backwards incompatibility
        had to be introduced: <option>-c</option> no longer implies
        <option>--no-psqlrc</option>.
       </para>
      </listitem>

      <listitem>
<!--
2015-07-02 [5671aaca8] Improve pg_restore's -t switch to match all types of rel
-->
       <para>
        Improve <application>pg_restore</>'s <option>-t</option> switch to
        match all types of relations, not only plain tables (Craig Ringer)
       </para>
      </listitem>

      <listitem>
<!--
2016-02-12 [59a884e98] Change delimiter used for display of NextXID
-->
       <para>
        Change the display format of <literal>NextXID</> in
        <application>pg_controldata</> and related places (Joe Conway,
        Bruce Momjian)
       </para>

       <para>
        Display epoch-and-transaction-ID values in the format
        <replaceable>number</><literal>:</><replaceable>number</>.
        The previous format
        <replaceable>number</><literal>/</><replaceable>number</> was
        confusingly similar to that used for <acronym>LSN</>s.
       </para>
      </listitem>

   </itemizedlist>

  </sect2>

  <sect2>
   <title>Changes</title>

   <para>
    Below you will find a detailed account of the changes between
    <productname>PostgreSQL</productname> 9.6 and the previous major
    release.
   </para>

   <sect3>
    <title>Server</title>

    <sect4>
     <title>Parallel Queries</title>

     <itemizedlist>

      <listitem>
<!--
2015-09-18 [4a4e6893a] Glue layer to connect the executor to the shm_mq mechani
2015-09-23 [a0d9f6e43] Add readfuncs.c support for plan nodes.
2015-09-28 [d1b7c1ffe] Parallel executor support.
2015-09-30 [3bd909b22] Add a Gather executor node.
2015-10-16 [ee7ca559f] Add a C API for parallel heap scans.
2015-10-16 [bfc78d719] Rewrite interaction of parallel mode with parallel execu
2015-10-16 [a53c06a13] Prohibit parallel query when the isolation level is seri
2015-11-02 [1efc7e538] Fix problems with ParamListInfo serialization mechanism.
2015-11-06 [6e71dd7ce] Modify tqueue infrastructure to support transient record
2015-11-11 [f0661c4e8] Make sequential scans parallel-aware.
2015-11-11 [80558c1f5] Generate parallel sequential scan plans in simple cases.
2015-12-09 [b287df70e] Allow EXPLAIN (ANALYZE, VERBOSE) to display per-worker s
2016-01-20 [45be99f8c] Support parallel joins, and make related improvements.
2016-02-03 [69d34408e] Allow parallel custom and foreign scans.
2016-02-07 [a1c1af2a1] Introduce group locking to prevent parallel processes fr
2016-02-07 [7c944bd90] Introduce a new GUC force_parallel_mode for testing purp
2016-02-25 [57a6a72b6] Enable parallelism for prepared statements and extended
2016-02-26 [7bea19d0a] On second thought, disable parallelism for prepared stat
2016-03-21 [e06a38965] Support parallel aggregation.
2016-04-05 [11c8669c0] Add parallel query support functions for assorted aggreg
2016-04-08 [25fe8b5f1] Add a 'parallel_degree' reloption.
2016-04-27 [59eb55127] Fix EXPLAIN VERBOSE output for parallel aggregate.
2016-06-09 [c9ce4a1c6] Eliminate "parallel degree" terminology.
2016-06-16 [75be66464] Invent min_parallel_relation_size GUC to replace a hard-
-->
       <para>
        Parallel queries (Robert Haas, Amit Kapila, David Rowley,
        many others)
       </para>

       <para>
        With 9.6, <productname>PostgreSQL</> introduces initial support
        for parallel execution of large queries.  Only strictly read-only
        queries where the driving table is accessed via a sequential scan
        can be parallelized.  Hash joins and nested loops can be performed
        in parallel, as can aggregation (for supported aggregates).
        Much remains to be done, but this is already a useful set of
        features.
       </para>

       <para>
        Use of parallel query execution can be controlled
        through the new configuration parameters <xref
        linkend="guc-max-parallel-workers-per-gather">,
        <xref linkend="guc-force-parallel-mode">,
        <xref linkend="guc-parallel-setup-cost">, <xref
        linkend="guc-parallel-tuple-cost">, and <xref
        linkend="guc-min-parallel-relation-size">.
       </para>
      </listitem>

      <listitem>
<!--
2015-09-16 [7aea8e4f2] Determine whether it's safe to attempt a parallel plan f
-->
       <para>
        Provide infrastructure for marking the parallel-safe status of
        functions  (Robert Haas, Amit Kapila)
       </para>
      </listitem>

     </itemizedlist>

    </sect4>

    <sect4>
     <title>Indexes</title>

     <itemizedlist>

      <listitem>
<!--
2015-09-02 [30bb26b5e] Allow usage of huge maintenance_work_mem for GIN build.
-->
       <para>
        Allow <link linkend="GIN"><acronym>GIN</></> index builds to
        make effective use of <xref linkend="guc-maintenance-work-mem">
        settings larger than 1 GB (Robert Abraham, Teodor Sigaev)
       </para>
      </listitem>

      <listitem>
<!--
2015-09-07 [e95680832] Add pages deleted from pending list to FSM
2015-09-23 [dc943ad95] Allow autoanalyze to add pages deleted from pending list
-->
       <para>
        Add pages deleted from a GIN index's pending list to the free space
        map immediately
        (Jeff Janes, Teodor Sigaev)
       </para>

       <para>
        This reduces bloat if the table is not vacuumed often.
       </para>
      </listitem>

      <listitem>
<!--
2016-01-28 [7f46eaf03] Add gin_clean_pending_list function to clean up GIN pend
-->
       <para>
        Add <link
        linkend="functions-admin-index"><function>gin_clean_pending_list()</></>
        function to allow manual invocation of pending-list cleanup for a
        GIN index, separately from vacuuming or analyzing the parent table
        (Jeff Janes)
       </para>
      </listitem>

      <listitem>
<!--
2015-09-09 [013ebc0a7] Microvacuum for GIST
2015-09-17 [22f519c92] Fix bug introduced by microvacuum for GiST
-->
       <para>
        Improve handling of dead index tuples in <link
        linkend="GiST">GiST</> indexes (Anastasia Lubennikova)
       </para>

       <para>
        Dead index tuples are now marked as such when an index scan notices
        that the corresponding heap tuple is dead.  When inserting tuples,
        marked-dead tuples will be removed if needed to make space on
        the page.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-30 [acdf2a8b3] Introduce SP-GiST operator class over box.
-->
       <para>
        Add an <link linkend="SPGiST">SP-GiST</link> operator class for
        type <type>box</> (Alexander Lebedev)
       </para>
      </listitem>

     </itemizedlist>

    </sect4>

    <sect4>
     <title>Sorting</title>

     <itemizedlist>

      <listitem>
<!--
2016-04-08 [071180377] Use quicksort, not replacement selection, for external s
2016-03-17 [0011c0091] Improve memory management for external sorts.
-->
       <para>
        Improve sorting performance by using quicksort, not replacement
        selection sort, when performing external sort steps (Peter
        Geoghegan)
       </para>

       <para>
        The new approach makes better use of the <acronym>CPU</> cache
        for typical cache sizes and data volumes.  Where necessary,
        the behavior can be adjusted via the new configuration parameter
        <xref linkend="guc-replacement-sort-tuples">.
       </para>
      </listitem>

      <listitem>
<!--
2015-10-09 [0e57b4d8b] Speed up text sorts where the same strings occur multipl
2015-10-20 [5be94a9eb] Be a bit more rigorous about how we cache strcoll and st
-->
       <para>
        Speed up text sorts where the same string occurs multiple times
        (Peter Geoghegan)
       </para>
      </listitem>

      <listitem>
<!--
2015-11-06 [a76ef15d9] Add sort support routine for the UUID data type.
2016-02-03 [b47b4dbf6] Extend sortsupport for text to more opclasses.
2016-02-17 [f1f5ec1ef] Reuse abbreviated keys in ordered [set] aggregates.
-->
       <para>
        Speed up sorting of <type>uuid</>, <type>bytea</>, and
        <type>char(n)</> fields by using <quote>abbreviated</> keys
        (Peter Geoghegan)
       </para>

       <para>
        Support for abbreviated keys has also been
        added to the non-default operator classes <link
        linkend="indexes-opclass"><literal>text_pattern_ops</></>,
        <literal>varchar_pattern_ops</>, and
        <literal>bpchar_pattern_ops</>.  Processing of ordered-set
        aggregates can also now exploit abbreviated keys.
       </para>
      </listitem>

      <listitem>
<!--
2015-12-16 [b648b7034] Speed up CREATE INDEX CONCURRENTLY's TID sort.
-->
       <para>
        Speed up <command>CREATE INDEX CONCURRENTLY</> by treating
        <acronym>TID</>s as 64-bit integers during sorting (Peter
        Geoghegan)
       </para>
      </listitem>

     </itemizedlist>

    </sect4>

    <sect4>
     <title>Locking</title>

     <itemizedlist>

      <listitem>
<!--
2015-08-06 [0e141c0fb] Reduce ProcArrayLock contention by removing backends in
2015-09-03 [4aec49899] Assorted code review for recent ProcArrayLock patch.
-->
       <para>
        Reduce contention for the <literal>ProcArrayLock</> (Amit Kapila,
        Robert Haas)
       </para>
      </listitem>

      <listitem>
<!--
2015-12-15 [6150a1b08] Move buffer I/O and content LWLocks out of the main tran
-->
       <para>
        Improve performance by moving buffer content locks into the buffer
        descriptors (Andres Freund, Simon Riggs)
       </para>
      </listitem>

      <listitem>
<!--
2016-04-10 [48354581a] Allow Pin/UnpinBuffer to operate in a lockfree manner.
-->
       <para>
        Replace shared-buffer header spinlocks with atomic operations to
        improve scalability (Alexander Korotkov, Andres Freund)
       </para>
      </listitem>

      <listitem>
<!--
2016-04-10 [008608b9d] Avoid the use of a separate spinlock to protect a LWLock
-->
       <para>
        Use atomic operations, rather than a spinlock, to protect an
        <literal>LWLock</>'s wait queue (Andres Freund)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-23 [44ca4022f] Partition the freelist for shared dynahash tables.
-->
       <para>
        Partition the shared hash table freelist to reduce contention on
        multi-<acronym>CPU</>-socket servers (Aleksander Alekseev)
       </para>
      </listitem>

      <listitem>
<!--
2016-01-09 [687f2cd7a] Avoid pin scan for replay of XLOG_BTREE_VACUUM
2016-04-03 [3e4b7d879] Avoid pin scan for replay of XLOG_BTREE_VACUUM in all ca
-->
       <para>
        Reduce interlocking on standby servers during the replay of btree
        index vacuuming operations (Simon Riggs)
       </para>

       <para>
        This change avoids substantial replication delays that sometimes
        occurred while replaying such operations.
       </para>
      </listitem>

     </itemizedlist>

    </sect4>

    <sect4>
     <title>Optimizer Statistics</title>

     <itemizedlist>

      <listitem>
<!--
2016-04-01 [be4b4dc75] Omit null rows when applying the Haas-Stokes estimator f
2016-04-01 [3d3bf62f3] Omit null rows when setting the threshold for what's a m
2016-04-04 [391159e03] Partially revert commit 3d3bf62f30200500637b24fdb7b992a9
-->
       <para>
        Improve <command>ANALYZE</>'s estimates for columns with many nulls
        (Tomas Vondra, Alex Shulgin)
       </para>

       <para>
        Previously <command>ANALYZE</> tended to underestimate the number
        of non-<literal>NULL</> distinct values in a column with many
        <literal>NULL</>s, and was also inaccurate in computing the
        most-common values.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-04 [84f9a35e3] Improve estimate of distinct values in estimate_num_grou
-->
       <para>
        Improve planner's estimate of the number of distinct values in
        a query result (Tomas Vondra)
       </para>
      </listitem>

      <listitem>
<!--
2016-04-08 [137805f89] Use Foreign Key relationships to infer multi-column join
2016-06-07 [77ba61080] Revert "Use Foreign Key relationships to infer multi-col
2016-06-18 [100340e2d] Restore foreign-key-aware estimation of join relation si
-->
       <para>
        Use foreign key relationships to infer selectivity for join
        predicates (Tomas Vondra, David Rowley)
       </para>

       <para>
        If a table <literal>t</> has a foreign key restriction, say
        <literal>(a,b) REFERENCES r (x,y)</>, then a <literal>WHERE</>
        condition such as <literal>t.a = r.x AND t.b = r.y</> cannot
        select more than one <literal>r</> row per <literal>t</> row.
        The planner formerly considered <literal>AND</> conditions
        to be independent and would often drastically misestimate
        selectivity as a result.  Now it compares the <literal>WHERE</>
        conditions to applicable foreign key constraints and produces
        better estimates.
       </para>
      </listitem>

     </itemizedlist>

    </sect4>

    <sect4>
     <title><command>VACUUM</></title>

     <itemizedlist>

      <listitem>
<!--
2016-03-01 [a892234f8] Change the format of the VM fork to add a second bit per
2016-03-08 [77a1d1e79] Department of second thoughts: remove PD_ALL_FROZEN.
2016-03-10 [fd31cd265] Don't vacuum all-frozen pages.
2016-03-11 [7087166a8] pg_upgrade: Convert old visibility map format to new for
2016-06-17 [ede62e56f] Add VACUUM (DISABLE_PAGE_SKIPPING) for emergencies.
2016-07-18 [eca0f1db1] Clear all-frozen visibilitymap status when locking tuple
2016-08-04 [e7caacf73] Fix hard to hit race condition in heapam's tuple locking
-->
       <para>
        Avoid re-vacuuming pages containing only frozen tuples (Masahiko
        Sawada, Robert Haas, Andres Freund)
       </para>

       <para>
        Formerly, anti-wraparound vacuum had to visit every page of
        a table, even pages where there was nothing to do.  Now, pages
        containing only already-frozen tuples are identified in the table's
        visibility map, and can be skipped by vacuum even when doing
        transaction wraparound prevention.  This should greatly reduce the
        cost of maintaining large tables containing mostly-unchanged data.
       </para>

       <para>
        If necessary, vacuum can be forced to process all-frozen
        pages using the new <literal>DISABLE_PAGE_SKIPPING</> option.
        Normally, this should never be needed but it might help in
        recovering from visibility-map corruption.
       </para>
      </listitem>

      <listitem>
<!--
2015-12-30 [e84290823] Avoid useless truncation attempts during VACUUM.
-->
       <para>
        Avoid useless heap-truncation attempts during <command>VACUUM</>
        (Jeff Janes, Tom Lane)
       </para>

       <para>
        This change avoids taking an exclusive table lock in some cases
        where no truncation is possible.  The main benefit comes from
        avoiding unnecessary query cancellations on standby servers.
       </para>
      </listitem>

     </itemizedlist>

    </sect4>

    <sect4>
     <title>General Performance</title>

     <itemizedlist>

      <listitem>
<!--
2016-04-08 [848ef42bb] Add the "snapshot too old" feature
2016-05-06 [2cc41acd8] Fix hash index vs "snapshot too old" problemms
2016-05-06 [7e3da1c47] Mitigate "snapshot too old" performance regression on NU
2016-08-03 [3e2f3c2e4] Prevent "snapshot too old" from trying to return pruned
2016-08-07 [9ee1cf04a] Fix TOAST access failure in RETURNING queries.
-->
       <para>
        Allow old <acronym>MVCC</> snapshots to be invalidated after a
        configurable timeout (Kevin Grittner)
       </para>

       <para>
        Normally, deleted tuples cannot be physically removed by
        vacuuming until the last transaction that could <quote>see</>
        them is gone.  A transaction that stays open for a long
        time can thus cause considerable table bloat because
        space cannot be recycled.  This feature allows setting
        a time-based limit, via the new configuration parameter
        <xref linkend="guc-old-snapshot-threshold">, on how long an
        <acronym>MVCC</> snapshot is guaranteed to be valid.  After that,
        dead tuples are candidates for removal.  A transaction using an
        outdated snapshot will get an error if it attempts to read a page
        that potentially could have contained such data.
       </para>
      </listitem>

      <listitem>
<!--
2016-02-11 [d4c3a156c] Remove GROUP BY columns that are functionally dependent
-->
       <para>
        Avoid computing <literal>GROUP BY</> columns if they are
        functionally dependent on other columns (David Rowley)
       </para>

       <para>
        If a <literal>GROUP BY</> clause includes all columns of a
        non-deferred primary key, as well as other columns of the same
        table, those other columns are redundant and can be dropped
        from the grouping.  This saves computation in many common cases.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-11 [9118d03a8] When appropriate, postpone SELECT output expressions til
2016-03-25 [d543170f2] Don't split up SRFs when choosing to postpone SELECT out
-->
       <para>
        When appropriate, postpone evaluation of <command>SELECT</>
        output expressions until after an <literal>ORDER BY</> sort
        (Konstantin Knizhnik)
       </para>

       <para>
        This change ensures that volatile or expensive functions in the
        output list are executed in the order suggested by <literal>ORDER
        BY</>, and that they are not evaluated more times than required
        when there is a <literal>LIMIT</> clause.  Previously, these
        properties held if the ordering was performed by an index scan or
        pre-merge-join sort, but not if it was performed by a top-level
        sort.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-31 [f9aefcb91] Support using index-only scans with partial indexes in m
-->
       <para>
        Allow use of an <link linkend="indexes-index-only-scans">index-only
        scan</link> on a partial index when the index's <literal>WHERE</>
        clause references columns which are not indexed (Tomas Vondra,
        Kyotaro Horiguchi)
       </para>

       <para>
        For example, <command>CREATE INDEX tidx_partial ON t(b) WHERE a
        &gt; 0</> could not previously be used for an index-only scan by a
        query that only referenced <literal>a</> in its <literal>WHERE</>
        clause because <literal>a</> is not an indexed value like
        <literal>b</> is.
       </para>

      </listitem>

      <listitem>
<!--
2016-03-10 [9cd00c457] Checkpoint sorting and balancing.
-->
       <para>
        Perform checkpoint writes in sorted order (Fabien Coelho,
        Andres Freund)
       </para>

       <para>
        Previously, checkpoints wrote out dirty pages in whatever order
        they happen to appear in shared buffers, which usually is nearly
        random.  That performs poorly, especially on rotating media.
        This change causes checkpoint-driven writes to be done in order
        by file and block number, and to be balanced across tablespaces.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-10 [428b1d6b2] Allow to trigger kernel writeback after a configurable n
2016-04-13 [fa11a09fe] Fix assorted portability issues with using msync() for d
2016-04-24 [8f91d87d4] Fix documentation & config inconsistencies around 428b1d
2016-04-26 [72a98a639] Don't open formally non-existent segments in _mdfd_getse
2016-05-04 [a71248708] Fix transient mdsync() errors of truncated relations due
2016-02-16 [7975c5e0a] Allow the WAL writer to flush WAL at a reduced rate.
2016-06-10 [4bc0f165c] Change default of backend_flush_after GUC to 0 (disabled
-->
       <para>
        Where feasible, trigger kernel writeback after a configurable
        number of writes, to prevent accumulation of dirty data in kernel
        disk buffers (Fabien Coelho, Andres Freund)
       </para>

       <para>
        <productname>PostgreSQL</> writes data to the kernel's disk cache,
        from where it will be flushed to physical storage in due time.
        Many operating systems are not smart about managing this and allow
        large amounts of dirty data to accumulate before deciding to flush
        it all at once, leading to long delays for new I/O requests.
        This change attempts to alleviate this problem by explicitly
        requesting data flushes after a configurable interval.
       </para>

       <para>
        On Linux, <function>sync_file_range()</> is used for this purpose,
        and the feature is on by default on Linux because that function has few
        downsides.  This sync capability is also available on other platforms
        that have <function>msync()</> or <function>posix_fadvise()</>,
        but those interfaces have some undesirable side-effects so the
        feature is disabled by default on non-Linux platforms.
       </para>

       <para>
        The new configuration parameters <xref
        linkend="guc-backend-flush-after">, <xref
        linkend="guc-bgwriter-flush-after">, <xref
        linkend="guc-checkpoint-flush-after">, and <xref
        linkend="guc-wal-writer-flush-after"> control this behavior.
       </para>
      </listitem>

      <listitem>
<!--
2015-08-04 [804163bc2] Share transition state between different aggregates when
-->
       <para>
        Improve aggregate-function performance by sharing calculations
        across multiple aggregates if they have the same arguments and
        transition functions (David Rowley)
       </para>

       <para>
        For example, <command>SELECT AVG(x), SUM(x) FROM x</> can use a
        single per-row compuation for both aggregates.
       </para>
      </listitem>

      <listitem>
<!--
2015-08-26 [8a7d07018] Speed up HeapTupleSatisfiesMVCC() by replacing the XID-i
-->
       <para>
        Speed up visibility tests for recently-created tuples by checking
        our transaction snapshot, not <structname>pg_clog</>, to decide
        if the source transaction should be considered committed (Jeff
        Janes, Tom Lane)
       </para>
      </listitem>

      <listitem>
<!--
2016-02-15 [db76b1efb] Allow SetHintBits() to succeed if the buffer's LSN is ne
-->
       <para>
        Allow tuple hint bits to be set sooner than before (Andres Freund)
       </para>
      </listitem>

      <listitem>
<!--
2016-01-20 [978b2f65a] Speedup 2PC by skipping two phase state files in normal
2016-03-10 [e0694cf9c] Reduce size of two phase file header
-->
       <para>
        Improve performance of short-lived prepared transactions (Stas
        Kelvich, Simon Riggs, Pavan Deolasee)
       </para>

       <para>
        Two-phase commit information is now written only to <acronym>WAL</>
        during <command>PREPARE TRANSACTION</>, and read from
        <acronym>WAL</> during <command>COMMIT PREPARED</>.  A separate
        state file is created only if the pending transaction does not
        get committed or aborted by the time of the next checkpoint.
       </para>
      </listitem>

      <listitem>
<!--
2015-12-08 [25c539233] Improve performance in freeing memory contexts
-->
       <para>
        Improve performance of memory context destruction (Jan Wieck)
       </para>
      </listitem>

      <listitem>
<!--
2016-01-26 [cc988fbb0] Improve ResourceOwners' behavior for large numbers of ow
-->
       <para>
        Improve performance of resource owners with many tracked objects
        (Aleksander Alekseev)
       </para>
      </listitem>

      <listitem>
<!--
2016-02-06 [aa2387e2f] Improve speed of timestamp/time/date output functions.
-->
       <para>
        Improve speed of the output functions for <type>timestamp</>,
        <type>time</>, and <type>date</> data types (David Rowley,
        Andres Freund)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-10 [37c54863c] Rework wait for AccessExclusiveLocks on Hot Standby
-->
       <para>
        Avoid some unnecessary cancellations of hot-standby queries
        during replay of actions that take <literal>AccessExclusive</>
        locks (Jeff Janes)
       </para>
      </listitem>

      <listitem>
<!--
2016-04-08 [719c84c1b] Extend relations multiple blocks at a time to improve sc
-->
       <para>
        Extend relations multiple blocks at a time when there is contention
        for the relation's extension lock (Dilip Kumar)
       </para>

       <para>
        This improves scalability by decreasing contention.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-08 [5364b357f] Increase maximum number of clog buffers.
-->
       <para>
        Increase the number of clog buffers for better scalability (Amit
        Kapila, Andres Freund)
       </para>
      </listitem>

      <listitem>
<!--
2015-07-05 [6c82d8d1f] Further reduce overhead for passing plpgsql variables to
-->
       <para>
        Speed up expression evaluation in <application>PL/pgSQL</> by
        keeping <literal>ParamListInfo</> entries for simple variables
        valid at all times (Tom Lane)
       </para>
      </listitem>

      <listitem>
<!--
2015-07-06 [4f33621f3] Don't set SO_SNDBUF on recent Windows versions that have
-->
       <para>
        Avoid reducing the <literal>SO_SNDBUF</> setting below its default
        on recent Windows versions (Chen Huajun)
       </para>
      </listitem>

     </itemizedlist>

    </sect4>

    <sect4>
     <title>Monitoring</title>

     <itemizedlist>

      <listitem>
<!--
2016-03-15 [c16dc1aca] Add simple VACUUM progress reporting.
-->
       <para>
        Add <link
        linkend="pg-stat-progress-vacuum-view"><structname>pg_stat_progress_vacuum</></link>
        system view to provide progress reporting for <command>VACUUM</>
        operations (Amit Langote, Robert Haas, Vinayak Pokale, Rahila Syed)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-05 [dc7d70ea0] Expose control file data via SQL accessible functions.
-->
       <para>
        Add <link
        linkend="functions-controldata"><function>pg_control_system()</></>,
        <function>pg_control_checkpoint()</>,
        <function>pg_control_recovery()</>, and
        <function>pg_control_init()</> functions to expose fields of
        <filename>pg_control</> to <acronym>SQL</> (Joe Conway, Michael
        Paquier)
       </para>
      </listitem>

      <listitem>
<!--
2016-02-17 [a5c43b886] Add new system view, pg_config
-->
       <para>
        Add <link linkend="view-pg-config"><structname>pg_config</></link>
        system view (Joe Conway)
       </para>

       <para>
        This view exposes the same information available from
        the <application>pg_config</> comand-line utility,
        namely assorted compile-time configuration information for
        <productname>PostgreSQL</>.
       </para>
      </listitem>

      <listitem>
<!--
2015-08-10 [3f811c2d6] Add confirmed_flush column to pg_replication_slots.
-->
       <para>
        Add a <structfield>confirmed_flush_lsn</> column to the <link
        linkend="view-pg-replication-slots"><structname>pg_replication_slots</></link>
        system view (Marko Tiikkaja)
       </para>
      </listitem>

      <listitem>
<!--
2016-01-07 [b1a9bad9e] pgstat: add WAL receiver status view & SRF
2016-06-29 [9ed551e0a] Add conninfo to pg_stat_wal_receiver
2016-07-07 [60d50769b] Rename pg_stat_wal_receiver.conn_info to conninfo.
-->
       <para>
        Add <link
        linkend="pg-stat-wal-receiver-view"><structname>pg_stat_wal_receiver</></link>
        system view to provide information about the state of a hot-standby
        server's <acronym>WAL</> receiver process (Michael Paquier)
       </para>
      </listitem>

      <listitem>
<!--
2016-02-22 [52f5d578d] Create a function to reliably identify which sessions bl
-->
       <para>
        Add <link
        linkend="functions-info-session-table"><function>pg_blocking_pids()</></>
        function to reliably identify which sessions block which others
        (Tom Lane)
       </para>

       <para>
        This function returns an array of the process IDs of any
        sessions that are blocking the session with the given process ID.
        Historically users have obtained such information using a self-join
        on the <structname>pg_locks</> view.  However,  it is unreasonably
        tedious to do it that way with any modicum of correctness, and
        the addition of parallel queries has made the approach entirely
        impractical, since locks might be held or awaited by child worker
        processes rather than the session's main process.
       </para>
      </listitem>

      <listitem>
<!--
2016-01-12 [e63bb4549] Add new user fn pg_current_xlog_flush_location()
-->
       <para>
        Add function <link
        linkend="functions-admin-backup-table"><function>pg_current_xlog_flush_location()</></>
        to expose the current transaction log flush location (Tomas Vondra)
       </para>
      </listitem>

      <listitem>
<!--
2015-07-17 [a04bb65f7] Add new function pg_notification_queue_usage.
-->
       <para>
        Add function <link
        linkend="functions-info-session-table"><function>pg_notification_queue_usage()</></>
        to report how full the <command>NOTIFY</> queue is (Brendan Jurd)
       </para>
      </listitem>

      <listitem>
<!--
2015-08-25 [7b5ef8f2d] Limit the verbosity of memory context statistics dumps.
-->
       <para>
        Limit the verbosity of memory context statistics dumps (Tom Lane)
       </para>

       <para>
        The memory usage dump output to the postmaster log during an
        out-of-memory failure now summarizes statistics when there are a
        large number of memory contexts, rather than possibly generating
        a very large report.  There is also a <quote>grand total</>
        summary line now.
       </para>
      </listitem>

     </itemizedlist>

    </sect4>

    <sect4>
     <title><acronym>Authentication</></title>

     <itemizedlist>

      <listitem>
<!--
2016-04-08 [34c33a1f0] Add BSD authentication method.
-->
       <para>
        Add an <literal>bsd</> authentication method to allow the use of
        the <systemitem class="osname">BSD</> Authentication service for
        <productname>PostgreSQL</> client authentication (Marisa Emerson)
       </para>

       <para>
        BSD Authentication is currently only available on <systemitem
        class="osname">OpenBSD</>.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-08 [2f1d2b7a7] Set PAM_RHOST item for PAM authentication
-->
       <para>
        When using <acronym>PAM</> authentication, provide the client
        IP address or host name to <acronym>PAM</> modules via the
        <literal>PAM_RHOST</> item (Grzegorz Sampolski)
       </para>
      </listitem>

      <listitem>
<!--
2016-01-07 [5e0b5dcab] Provide more detail in postmaster log for password authe
-->
       <para>
        Provide detail in the postmaster log during more password
        authentication failures (Tom Lane)
       </para>

       <para>
        All ordinarily-reachable password authentication failure cases
        should now provide specific <literal>DETAIL</> fields in the log.
       </para>
      </listitem>

      <listitem>
<!--
2015-09-06 [643beffe8] Support RADIUS passwords up to 128 characters
-->
       <para>
        Support <acronym>RADIUS</> passwords up to 128 characters long
        (Marko Tiikkaja)
       </para>
      </listitem>

      <listitem>
<!--
2016-04-08 [35e2e357c] Add authentication parameters compat_realm and upn_usena
-->
       <para>
        Add new <acronym>SSPI</> authentication parameters
        <varname>compat_realm</> and <varname>upn_username</> to control
        whether <productname>NetBIOS</> or <productname>Kerberos</>
        realm names and user names are used during <acronym>SSPI</>
        authentication (Christian Ullrich)
       </para>
      </listitem>

     </itemizedlist>

    </sect4>

    <sect4>
     <title>Server Configuration</title>

     <itemizedlist>

      <listitem>
<!--
2016-03-16 [c6dda1f48] Add idle_in_transaction_session_timeout.
-->
       <para>
        Allow sessions to be terminated automatically if they are in
        idle-in-transaction state for too long (Vik Fearing)
       </para>

       <para>
        This behavior is controlled by the new configuration parameter
        <xref linkend="guc-idle-in-transaction-session-timeout">.  It can
        be useful to prevent forgotten transactions from holding locks
        or preventing vacuum cleanup for too long.
       </para>
      </listitem>

      <listitem>
<!--
2015-09-08 [1aba62ec6] Allow per-tablespace effective_io_concurrency
-->
       <para>
        Allow <varname>effective_io_concurrency</> to be set per-tablespace
        to support cases where different tablespaces have different I/O
        characteristics (Julien Rouhaud)
       </para>
      </listitem>

      <listitem>
<!--
2016-02-02 [7d17e683f] Add support for systemd service notifications
-->
       <para>
        Add configure option <option>--with-systemd</> to enable
        calling <function>sd_notify()</> at server start and stop (Peter
        Eisentraut)
       </para>

       <para>
        This allows the use of <application>systemd</> service units of
        type <literal>notify</>, which greatly simplifies the management
        of <productname>PostgreSQL</> under <application>systemd</>.
       </para>
      </listitem>

      <listitem>
<!--
2015-09-07 [f828654e1] Add log_line_prefix option 'n' for Unix epoch.
2015-09-07 [b1e1862a1] Coordinate log_line_prefix options 'm' and 'n' to share
-->
       <para>
        Add <varname>log_line_prefix</> option <literal>%n</> to print
        the current time as a Unix epoch, with milliseconds (Tomas Vondra,
        Jeff Davis)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-16 [f4c454e9b] Add syslog_sequence_numbers parameter
2016-03-16 [fc201dfd9] Add syslog_split_messages parameter
-->
       <para>
        Add <xref linkend="guc-syslog-sequence-numbers"> and <xref
        linkend="guc-syslog-split-messages"> configuration parameters
        to provide more control over the message format when logging to
        <systemitem>syslog</> (Peter Eisentraut)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-18 [b555ed810] Merge wal_level "archive" and "hot_standby" into new nam
-->
       <para>
        Merge the <literal>archive</> and <literal>hot_standby</> values
        of the <xref linkend="guc-wal-level"> configuration parameter
        into a single new value <literal>replica</> (Peter Eisentraut)
       </para>

       <para>
        Making a distinction between these settings is no longer useful,
        and is part of a planned future simplification of replication
        setup.  The old names are still accepted but are converted
        internally.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-19 [9a83564c5] Allow SSL server key file to have group read access if o
-->
       <para>
        Allow the server's <acronym>SSL</> key file to have group read
        access if owned by root (Christoph Berg) <!-- Windows handling? -->
       </para>

       <para>
        Formerly, we insisted the key file be owned by the
        user running the <productname>PostgreSQL</> server, but
        that is inconvenient on some systems (such as <systemitem
        class="osname">Debian</>) that are configured to manage
        certificates centrally.  Therefore, allow the case where the key
        file is owned by <literal>root</> and has group read access.
        It is up to the operating system administrator to ensure that
        the group does not include any untrusted users.
       </para>
      </listitem>

     </itemizedlist>

    </sect4>

    <sect4>
     <title>Reliability</title>

     <itemizedlist>

      <listitem>
<!--
2015-11-12 [ac1d7945f] Make idle backends exit if the postmaster dies.
-->
       <para>
        Force backends to exit if the postmaster dies (Rajeev Rastogi,
        Robert Haas)
       </para>

       <para>
        Under normal circumstances the postmaster should always outlive
        its child processes.  If for some reason the postmaster dies,
        force backend sessions to exit with an error.  Formerly, existing
        backends would continue to run until their clients disconnect,
        but that is unsafe and inefficient.  It also prevents a new
        postmaster from being started until the last old backend has
        exited.  Backends will detect postmaster death when waiting for
        client I/O, so the exit will not be instantaneous, but it in most
        cases should happen no later than the end of the current query.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-07 [fcff8a575] Detect SSI conflicts before reporting constraint violati
-->
       <para>
        Check for serializability conflicts before reporting
        constraint-violation failures (Thomas Munro)
       </para>

       <para>
        When using serializable transaction isolation, it is desirable
        that any error due to concurrent transactions should manifest
        as a serialization failure, thereby cueing the application that
        a retry might succeed.  Unfortunately, this does not reliably
        happen for duplicate-key failures caused by concurrent insertions.
        This change ensures that such an error will be reported as a
        serialization error if the application explicitly checked for
        the presence of a conflicting key (and did not find it) earlier
        in the transaction.
       </para>
      </listitem>

      <listitem>
<!--
XXX this is pending backpatch, may need to remove
2016-04-26 [c6ff84b06] Emit invalidations to standby for transactions without x
-->
       <para>
        Ensure that invalidation messages are recorded in <acronym>WAL</>
        even when issued by a transaction that has no <acronym>XID</>
        assigned (Andres Freund)
       </para>

       <para>
        This fixes some corner cases in which transactions on standby
        servers failed to notice changes, such as new indexes.
       </para>
      </listitem>

      <listitem>
<!--
XXX this is pending backpatch, may need to remove
2016-04-28 [e2c79e14d] Prevent multiple cleanup process for pending list in GIN
-->
       <para>
        Prevent multiple processes from trying to clean a <acronym>GIN</>
        index's pending list concurrently (Teodor Sigaev, Jeff Janes)
       </para>

       <para>
        This had been intentionally allowed, but it causes race conditions
        that can result in vacuum missing index entries it needs to delete.
       </para>
      </listitem>

     </itemizedlist>

    </sect4>

   </sect3>

   <sect3>
    <title>Replication and Recovery</title>

     <itemizedlist>

      <listitem>
<!--
2016-04-06 [989be0810] Support multiple synchronous standby servers.
2016-04-27 [4c804fbdf] Clean up parsing of synchronous_standby_names GUC variab
2016-04-30 [17d5db352] Remove warning about num_sync being too large in synchro
-->
       <para>
        Allow synchronous replication to support multiple simultaneous
        synchronous standby servers, not just one (Masahiko Sawada,
        Beena Emerson, Michael Paquier, Fujii Masao, Kyotaro Horiguchi)
       </para>

       <para>
        The number of standby servers that must acknowledge a commit
        before it is considered complete is now configurable as part of
        the <xref linkend="guc-synchronous-standby-names"> parameter.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-29 [314cbfc5d] Add new replication mode synchronous_commit = 'remote_ap
-->
       <para>
        Add new setting <literal>remote_apply</> for configuration
        parameter <xref linkend="guc-synchronous-commit"> (Thomas Munro)
       </para>

       <para>
        In this mode, the master waits for the transaction to be
        <emphasis>applied</> on the standby server, not just written
        to disk.  That means that you can count on a transaction started
        on the standby to see all commits previously acknowledged by
        the master.
       </para>
      </listitem>

      <listitem>
<!--
2015-08-11 [6fcd88511] Allow pg_create_physical_replication_slot() to reserve W
2015-09-06 [c314ead5b] Add ability to reserve WAL upon slot creation via replic
-->
       <para>
        Add a feature to the replication
        protocol, and a corresponding option to <link
        linkend="functions-replication-table"><function>pg_create_physical_replication_slot()</></>,
        to allow reserving <acronym>WAL</> immediately when creating a
        replication slot (Gurjeet Singh, Michael Paquier)
       </para>

       <para>
        This allows the creation of a replication slot to guarantee
        that all the <acronym>WAL</> needed for a base backup will be
        available.
       </para>
      </listitem>

      <listitem>
<!--
2015-07-28 [0dc848b03] pg_basebackup: Add -slot option
-->
       <para>
        Add a <option>--slot</option> option to
        <application>pg_basebackup</> (Peter Eisentraut)
       </para>

       <para>
        This lets <application>pg_basebackup</> use a replication
        slot defined for <acronym>WAL</> streaming.  After the base
        backup completes, selecting the same slot for regular streaming
        replication allows seamless startup of the new standby server.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-05 [711768546] Implement backup API functions for non-exclusive backups
2016-07-11 [87d84d67b] Fix start WAL filename for concurrent backups from stand
-->
       <para>
        Extend <link
        linkend="functions-admin-backup-table"><function>pg_start_backup()</></>
        and <function>pg_stop_backup()</> to support non-exclusive backups
        (Magnus Hagander)
       </para>
      </listitem>

     </itemizedlist>

   </sect3>

   <sect3>
    <title>Queries</title>

     <itemizedlist>

      <listitem>
<!--
2016-07-26 [d8411a6c8] Allow functions that return sets of tuples to return sim
-->
       <para>
        Allow functions that return sets of tuples to return simple
        <literal>NULL</>s (Andrew Gierth, Tom Lane)
       </para>

       <para>
        In the context of <literal>SELECT FROM function(...)</>, a function
        that returned a set of composite values was previously not allowed
        to return a plain <literal>NULL</> value as part of the set.
        Now that is allowed and interpreted as a row of <literal>NULL</>s.
        This avoids corner-case errors with, for example, unnesting an
        array of composite values.
       </para>
      </listitem>

      <listitem>
<!--
2016-08-03 [a3c7a993d] Make INSERT-from-multiple-VALUES-rows handle targetlist
-->
       <para>
        Fully support array subscripts and field selections in the
        target column list of an <command>INSERT</> with multiple
        <literal>VALUES</> rows (Tom Lane)
       </para>

       <para>
        Previously, such cases failed if the same target column was
        mentioned more than once, e.g., <literal>INSERT INTO tab (x[1],
        x[2]) VALUES ...</>.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-12 [23a27b039] Widen query numbers-of-tuples-processed counters to uint
2016-03-14 [74a379b98] Use repalloc_huge() to enlarge a SPITupleTable's tuple p
-->
       <para>
        Widen counters recording the number of tuples processed to 64 bits
        (Andreas Scherbaum)
       </para>

       <para>
        This change allows command tags, e.g. <command>SELECT</>, to
        correctly report tuple counts larger than 4 billion.  This also
        applies to PL/pgSQL's <command>GET DIAGNOSTICS ... ROW_COUNT</>
        command.
       </para>
      </listitem>

      <listitem>
<!--
2015-11-28 [8d32717b6] Avoid doing encoding conversions by double-conversion vi
-->
       <para>
        Avoid doing encoding conversions by converting through the
        <literal>MULE_INTERNAL</> encoding (Tom Lane)
       </para>

       <para>
        Previously, many conversions for Cyrillic and Central
        European single-byte encodings were done by converting to a
        related <literal>MULE_INTERNAL</> coding scheme and then to the
        destination encoding.  Aside from being inefficient, this meant
        that when the conversion encountered an untranslatable character,
        the error message would confusingly complain about failure to
        convert to or from <literal>MULE_INTERNAL</>, rather than the
        user-visible encoding.
       </para>
      </listitem>

      <listitem>
<!--
2016-01-28 [fbe5a3fb7] Only try to push down foreign joins if the user mapping
2016-07-15 [45639a052] Avoid invalidating all foreign-join cached plans when us
-->
       <para>
        Consider performing joins of foreign tables remotely only when the
        tables will be accessed under the same role ID (Shigeru Hanada,
        Ashutosh Bapat, Etsuro Fujita)
       </para>

       <para>
        Previously, the foreign join pushdown infrastructure left the
        question of security entirely up to individual foreign data
        wrappers, but it would be too easy for an <acronym>FDW</> to
        inadvertently open up subtle security hole.  So, make it the core
        code's job to determine which role ID will access each table,
        and do not attempt join pushdown unless the role is the same for
        all relevant relations.
       </para>
      </listitem>

     </itemizedlist>

   </sect3>

   <sect3>
    <title>Utility Commands</title>

     <itemizedlist>

      <listitem>
<!--
2015-11-27 [92e38182d] COPY (INSERT/UPDATE/DELETE .. RETURNING ..)
-->
       <para>
        Allow <command>COPY</> to copy the output of an
        <literal>INSERT</>/<literal>UPDATE</>/<literal>DELETE</>
        ... <literal>RETURNING</> query (Marko Tiikkaja)
       </para>

       <para>
        Previously, an intermediate <acronym>CTE</> had to be written to
        get this result.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-05 [f2fcad27d] Support ALTER THING .. DEPENDS ON EXTENSION
-->
       <para>
        Introduce <command>ALTER <replaceable>object</> DEPENDS ON
        EXTENSION</command> (Abhijit Menon-Sen)
       </para>

       <para>
        This command allows a database object to be marked as depending
        on an extension, so that it will be automatically dropped if
        the extension is dropped (without needing <literal>CASCADE</>).
        However, the object is not part of the extension, and thus will
        be dumped separately by <application>pg_dump</>.
       </para>
      </listitem>

      <listitem>
<!--
2015-11-19 [bc4996e61] Make ALTER .. SET SCHEMA do nothing, instead of throwing
-->
       <para>
        Make <command>ALTER <replaceable>object</> SET SCHEMA</> do nothing
        when the object is already in the requested schema, rather than
        throwing an error as it historically has for most object types
        (Marti Raudsepp)
       </para>
      </listitem>

      <listitem>
<!--
2015-07-14 [321eed5f0] Add ALTER OPERATOR command, for changing selectivity est
2015-12-31 [0dab5ef39] Fix ALTER OPERATOR to update dependencies properly.
-->
       <para>
        Add options to <command>ALTER OPERATOR</command> to allow changing
        the selectivity functions associated with an existing operator
        (Yury Zhuravlev)
       </para>
      </listitem>

      <listitem>
<!--
2015-07-29 [2cd40adb8] Add IF NOT EXISTS processing to ALTER TABLE ADD COLUMN
-->
       <para>
        Add an <option>IF NOT EXISTS</> option to <command>ALTER TABLE
        ADD COLUMN</> (Fabr&iacute;zio de Royes Mello)
       </para>
      </listitem>

      <listitem>
<!--
2015-08-14 [47167b790] Reduce lock levels for ALTER TABLE SET autovacuum storag
2016-03-10 [fcb4bfddb] Reduce lock level for altering fillfactor
-->
       <para>
        Reduce the lock strength needed by <command>ALTER TABLE</>
        when setting fillfactor and autovacuum-related relation options
        (Fabr&iacute;zio de Royes Mello, Simon Riggs)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-23 [473b93287] Support CREATE ACCESS METHOD
-->
       <para>
        Introduce <command>CREATE ACCESS METHOD</> to allow extensions
        to create index access methods (Alexander Korotkov, Petr
        Jel&iacute;nek)
       </para>
      </listitem>

      <listitem>
<!--
2015-10-03 [b67aaf21e] Add CASCADE support for CREATE EXTENSION.
-->
       <para>
        Add a <literal>CASCADE</> option to <command>CREATE
        EXTENSION</command> to automatically create extensions it depends
        on (Petr Jel&iacute;nek)
       </para>
      </listitem>

      <listitem>
<!--
2015-10-05 [b943f502b] Have CREATE TABLE LIKE add OID column if any LIKEd table
-->
       <para>
        Make <command>CREATE TABLE ... LIKE</> include an <type>OID</>
        column if any source table has one (Bruce Momjian)
       </para>
      </listitem>

      <listitem>
<!--
2015-12-16 [f27a6b15e] Mark CHECK constraints declared NOT VALID valid if creat
-->
       <para>
        If a <literal>CHECK</> constraint is declared <literal>NOT VALID</>
        in a table creation command, automatically mark it as valid
        (Amit Langote, Amul Sul)
       </para>

       <para>
        This is possible because the table has no existing rows.  This matches
        the longstanding behavior of <literal>FOREIGN KEY</> constraints.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-25 [c94959d41] Fix DROP OPERATOR to reset oprcom/oprnegate links to the
-->
       <para>
        Fix <command>DROP OPERATOR</> to clear
        <structname>pg_operator</>.<structfield>oprcom</> and
        <structname>pg_operator</>.<structfield>oprnegate</> links to
        the dropped operator (Roma Sokolov)
       </para>

       <para>
        Formerly such links were left as-is, which could pose a problem
        in the somewhat unlikely event that the dropped operator's
        <type>OID</> was reused for another operator.
       </para>
      </listitem>

      <listitem>
<!--
2016-07-11 [4d042999f] Print a given subplan only once in EXPLAIN.
-->
       <para>
        Do not show the same subplan twice in <command>EXPLAIN</> output
        (Tom Lane)
       </para>

       <para>
        In certain cases, typically involving SubPlan nodes in index
        conditions, <command>EXPLAIN</> would print data for the same
        subplan twice.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-16 [c34df8a00] Disallow creation of indexes on system columns (except f
-->
       <para>
        Disallow creation of indexes on system columns, except for
        <type>OID</> columns (David Rowley)
       </para>

       <para>
        Such indexes were never considered supported, and would very
        possibly misbehave since the system might change the system-column
        fields of a tuple without updating indexes.  However, previously
        there were no error checks to prevent them from being created.
       </para>
      </listitem>

     </itemizedlist>

   </sect3>

   <sect3>
    <title>Permissions Management</title>

    <itemizedlist>

      <listitem>
<!--
2016-04-06 [1574783b4] Use GRANT system to manage access to sensitive functions
-->
       <para>
        Use the privilege system to manage access to sensitive functions
        (Stephen Frost)
       </para>

       <para>
        Formerly, many security-sensitive functions contained hard-wired
        checks that would throw an error if they were called by a
        non-superuser role.  This forced the use of superuser roles for
        some relatively pedestrian tasks.  The hard-wired error checks
        are now gone in favor of making <application>initdb</> revoke the
        default public <literal>EXECUTE</> privilege on these functions.
        This allows installations to choose to grant usage of such
        functions to trusted roles that do not need all superuser
        privileges.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-08 [7a542700d] Create default roles
-->
       <para>
        Create some <link linkend="default-roles">built-in roles</link>
        that can be used to grant access to what were previously
        superuser-only functions (Stephen Frost)
       </para>
      </listitem>

    </itemizedlist>

   </sect3>

   <sect3>
    <title>Data Types</title>

    <itemizedlist>

      <listitem>
<!--
2016-04-07 [bb140506d] Phrase full text search.
2016-06-27 [028350f61] Make exact distance match for FTS phrase operator
2016-06-27 [3dbbd0f02] Do not fallback to AND for FTS phrase operator.
2016-06-27 [6734a1cac] Change predecence of phrase operator.
-->
       <para>
        Improve full-text search to support searching for phrases, that
        is, lexemes appearing adjacent to each other in a specific order,
        or with a specified distance between them (Teodor Sigaev, Oleg
        Bartunov, Dmitry Ivanov)
       </para>

       <para>
        A phrase-search query can be specified in <type>tsquery</>
        input using the new operators <literal>&lt;-&gt;</> and
        <literal>&lt;<replaceable>N</>&gt;</literal>.  The former means
        that the lexemes before and after it must appear adjacent to
        each other in that order.  The latter means they must be exactly
        <replaceable>N</> lexemes apart.
       </para>
      </listitem>

      <listitem>
<!--
2015-12-22 [6efbded6e] Allow omitting one or both boundaries in an array slice
-->
       <para>
        Allow omitting one or both boundaries in an array slice specifier,
        e.g. <literal>array_col[3:]</> (Yury Zhuravlev)
       </para>

       <para>
        Omitted boundaries are taken as the upper or lower limit of the
        corresponding array subscript.  This allows simpler specification
        for many common use-cases.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-16 [a70e13a39] Be more careful about out-of-range dates and timestamps.
-->
       <para>
        Be more careful about out-of-range dates and timestamps (Vitaly
        Burovoy)
       </para>

       <para>
        This change prevents unexpected out-of-range errors for
        <type>timestamp with time zone</> values very close to the
        implementation limits.  Previously, the <quote>same</> value might
        be accepted or not depending on the <varname>timezone</> setting,
        meaning that a dump and reload could fail on a value that had been
        accepted when presented.  Now the limits are enforced according
        to the equivalent <acronym>UTC</> time, not local time, so as to
        be independent of <varname>timezone</>.
       </para>

       <para>
        Also, <productname>PostgreSQL</> is now more careful to detect
        overflow in operations that compute new date or timestamp values,
        such as <type>date</> <literal>+</> <type>integer</>.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-30 [50861cd68] Improve portability of I/O behavior for the geometric ty
-->
       <para>
        For geometric data types, make sure <literal>infinity</> and
        <literal>NaN</> component values are treated consistently during
        input and output (Tom Lane)
       </para>

       <para>
        Such values will now always print the same as they would in
        a simple <type>float8</> column, and be accepted the same way
        on input.  Previously the behavior was platform-dependent.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-04 [d78a7d9c7] Improve support of Hunspell in ispell dictionary.
2016-03-11 [8829af47e] Fix merge affixes for numeric ones
2016-03-17 [f4ceed6ce] Improve support of Hunspell
-->
       <para>
        Upgrade the <literal>ispell</> dictionary to handle modern
        <productname>Hunspell</> files and support more languages
        (Artur Zakirov)
       </para>
      </listitem>

      <listitem>
<!--
2015-10-30 [12c9a0400] Implement lookbehind constraints in our regular-expressi
-->
       <para>
        Implement look-behind constraints in regular expressions (Tom Lane)
       </para>

       <para>
        A look-behind constraint is like a lookahead constraint in that it
        consumes no text; but it checks for existence (or nonexistence)
        of a match ending at the current point in the string, rather
        than one starting at the current point.  Similar features exist
        in many other regular-expression engines.
       </para>
      </listitem>

      <listitem>
<!--
2015-09-16 [b44d92b67] Sync regex code with Tcl 8.6.4.
-->
       <para>
        In regular expressions, if an apparent three-digit octal escape
        <literal>\</><replaceable>nnn</> would exceed 377 (255 decimal),
        assume it is a two-digit octal escape instead (Tom Lane)
       </para>

       <para>
        This makes the behavior match current <application>Tcl</> releases.
       </para>
      </listitem>

      <listitem>
<!--
2015-11-07 [c5e86ea93] Add "xid <> xid" and "xid <> int4" operators.
-->
       <para>
        Add transaction id operators <type>xid</> <literal>&lt;&gt;</>
        <type>xid</> and <type>xid</> <literal>&lt;&gt;</> <type>int4</>,
        for consistency with the corresponding equality operators
        (Michael Paquier)
       </para>
      </listitem>

    </itemizedlist>

   </sect3>

   <sect3>
    <title>Functions</title>

     <itemizedlist>

      <listitem>
<!--
2016-04-06 [0b62fd036] Add jsonb_insert
-->
       <para>
        Add <link
        linkend="functions-json-processing-table"><function>jsonb_insert()</></>
        function to insert a new element into a <type>jsonb</> array,
        or a not-previously-existing key into a <type>jsonb</> object
        (Dmitry Dolgov)
       </para>
      </listitem>

      <listitem>
<!--
2015-11-14 [7d9a4737c] Improve type numeric's calculations for ln(), log(), exp
2016-05-05 [18a02ad2a] Fix corner-case loss of precision in numeric pow() calcu
-->
       <para>
        Improve the accuracy of the <function>ln()</>, <function>log()</>,
        <function>exp()</>, and <function>pow()</> functions for type
        <type>numeric</> (Dean Rasheed)
       </para>
      </listitem>

      <listitem>
<!--
2016-01-05 [abb173392] Add scale(numeric)
-->
       <para>
        Add a <function>scale(numeric)</> function to extract the display
        scale of a <type>numeric</> value (Marko Tiikkaja)
       </para>
      </listitem>

      <listitem>
<!--
2016-01-22 [e1bd684a3] Add trigonometric functions that work in degrees.
-->
       <para>
        Add trigonometric functions that work in degrees (Dean Rasheed)
       </para>

       <para>
        For example, <link
        linkend="functions-math-trig-table"><function>sind()</></>
        measures its argument in degrees, whereas <function>sin()</>
        measures in radians.  These functions go to some lengths to
        deliver exact results for values where an exact result can be
        expected, e.g.  <literal>sind(30) = 0.5</literal>.
       </para>
      </listitem>

      <listitem>
<!--
2016-01-22 [fd5200c3d] Improve cross-platform consistency of Inf/NaN handling i
-->
       <para>
        Ensure that trigonometric functions handle <literal>infinity</>
        and <literal>NaN</> inputs per the <acronym>POSIX</> standard
        (Dean Rasheed)
       </para>

       <para>
        The <acronym>POSIX</> standard says that these functions should
        return <literal>NaN</> for NaN input, and should throw an error for
        out-of-range inputs including <literal>infinity</>.  Previously our
        behavior varied across platforms.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-29 [e511d878f] Allow to_timestamp(float8) to convert float infinity to
-->
       <para>
        Make <function>to_timestamp(float8)</> convert float
        <literal>infinity</> to timestamp <literal>infinity</> (Vitaly
        Burovoy)
       </para>

       <para>
        Formerly it just failed on an infinite input.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-11 [6943a946c] Tsvector editing functions
2016-05-05 [0b9a23443] Rename tsvector delete() to ts_delete(), and filter() to
-->
       <para>
        Add new functions for <type>tsvector</> data (Stas Kelvich)
       </para>

       <para>
        The new functions are <link
        linkend="textsearch-functions-table"><function>ts_delete()</></>,
        <function>ts_filter()</>, <function>unnest()</>,
        <function>tsvector_to_array()</>, <function>array_to_tsvector()</>,
        and a variant of <function>setweight()</> that sets the weight
        only for specified lexeme(s).
       </para>
      </listitem>

      <listitem>
<!--
2015-09-17 [9acb9007d] Fix oversight in tsearch type check
-->
       <para>
        Allow <function>ts_stat_sql()</> and
        <function>tsvector_update_trigger()</> to operate on values that
        are of types binary-compatible with the expected argument type,
        not just that argument type; for example allow <type>citext</>
        where <type>text</> is expected (Teodor Sigaev)
       </para>
      </listitem>

      <listitem>
<!--
2016-02-04 [6819514fc] Add num_nulls() and num_nonnulls() to count NULL argumen
-->
       <para>
        Add variadic functions <link
        linkend="functions-comparison-func-table"><function>num_nulls()</></>
        and <function>num_nonnulls()</> that count the number of their
        arguments that are null or non-null (Marko Tiikkaja)
       </para>

       <para>
        An example usage is <literal>CHECK(num_nonnulls(a,b,c) = 1)</>
        which asserts that exactly one of a,b,c is not <literal>NULL</>.
        These functions can also be used to count the number of null or
        nonnull elements in an array.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-18 [3187d6de0] Introduce parse_ident()
-->
       <para>
        Add function <link
        linkend="functions-string-other"><function>parse_ident()</></>
        to split a qualified, possibly quoted <acronym>SQL</> identifier
        into its parts (Pavel Stehule)
       </para>
      </listitem>

      <listitem>
<!--
2015-10-05 [28b3a3d41] to_number():  allow 'V' to divide by 10^(the number of d
-->
       <para>
        In <link
        linkend="functions-formatting-table"><function>to_number()</></>,
        interpret <literal>V</> as dividing by 10 to the power of the
        number of digits following <literal>V</> (Bruce Momjian)
       </para>

       <para>
        This makes it operate in an inverse fashion to
        <function>to_char()</>.
       </para>
      </listitem>

      <listitem>
<!--
2016-01-05 [ea0d494da] Make the to_reg*() functions accept text not cstring.
-->
       <para>
        Make the <function>to_reg*()</> functions accept type <type>text</>
        not <type>cstring</> (Petr Korobeinikov)
       </para>

       <para>
        This avoids the need to write an explicit cast in most cases
        where the argument is not a simple literal constant.
       </para>
      </listitem>

      <listitem>
<!--
2016-02-20 [53874c522] Add pg_size_bytes() to parse human-readable size strings
-->
       <para>
        Add <link
        linkend="functions-admin-dbsize"><function>pg_size_bytes()</></>
        function to convert human-readable size strings to numbers (Pavel
        Stehule, Vitaly Burovoy, Dean Rasheed)
       </para>

       <para>
        This function converts strings like those produced by
        <function>pg_size_pretty()</> into bytes.  An example
        usage is <literal>SELECT oid::regclass FROM pg_class WHERE
        pg_total_relation_size(oid) &gt; pg_size_bytes('10 GB')</>.
       </para>
      </listitem>

      <listitem>
<!--
2015-11-06 [8a1fab36a] pg_size_pretty: Format negative values similar to positi
-->
       <para>
        In <link
        linkend="functions-admin-dbsize"><function>pg_size_pretty()</></>,
        format negative numbers similarly to positive ones (Adrian
        Vondendriesch)
       </para>

       <para>
        Previously, negative numbers were never abbreviated, just printed
        in bytes.
       </para>
      </listitem>

      <listitem>
<!--
2015-07-02 [10fb48d66] Add an optional missing_ok argument to SQL function curr
-->
       <para>
        Add an optional <replaceable>missing_ok</> argument to the <link
        linkend="functions-admin-set-table"><function>current_setting()</></>
        function (David Christensen)
       </para>

       <para>
        This allows avoiding an error for an unrecognized parameter
        name, and instead return a <literal>NULL</>.
       </para>
      </listitem>

      <listitem>
<!--
2016-07-26 [976b24fb4] Change various deparsing functions to return NULL for in
2016-07-29 [3153b1a52] Eliminate a few more user-visible "cache lookup failed"
2016-08-07 [8a8c6b538] Fix crash when pg_get_viewdef_name_ext() is passed a non
-->
       <para>
        Change various catalog-inspection functions to return
        <literal>NULL</> for invalid input (Michael Paquier)
       </para>

       <para>
        <link
        linkend="functions-info-catalog-table"><function>pg_get_viewdef()</></>
        now returns <literal>NULL</> if given an invalid view <type>OID</>,
        and several similar functions likewise return <literal>NULL</> for
        bad input.  Previously, such cases usually led to <quote>cache
        lookup failed</> errors, which are not meant to occur in
        user-facing cases.
       </para>
      </listitem>

      <listitem>
<!--
2016-08-02 [dd5eb805d] Remove unused arguments from pg_replication_origin_xact_
-->
       <para>
        Fix <link
        linkend="pg-replication-origin-xact-reset"><function>pg_replication_origin_xact_reset()</></>
        to not have any arguments (Fujii Masao)
       </para>

       <para>
        The documentation said that it has no arguments, and the C code did
        not expect any arguments, but the entry in <structname>pg_proc</>
        mistakenly specified two arguments.
       </para>
      </listitem>

     </itemizedlist>

   </sect3>

   <sect3>
    <title>Server-Side Languages</title>

    <itemizedlist>

      <listitem>
<!--
2015-08-21 [fcdfce682] Detect mismatched CONTINUE and EXIT statements at plpgsq
-->
       <para>
        In <link linkend="plpgsql">PL/pgSQL</link>, detect mismatched
        <command>CONTINUE</> and <command>EXIT</> statements while
        compiling PL/pgSQL functions, rather than at execution time
        (Jim Nasby)
       </para>
      </listitem>

      <listitem>
<!--
2016-04-08 [5c3c3cd0a] Enhanced custom error in PLPythonu
2016-06-11 [020140d84] PL/Python: Rename new keyword arguments of plpy.error()
2016-07-02 [3a4a33ad4] PL/Python: Report argument parsing errors using exceptio
-->
       <para>
        Extend <application>PL/Python</>'s error-reporting and
        message-reporting functions to allow specifying additional message
        fields besides the primary error message (Pavel Stehule)
       </para>
      </listitem>

      <listitem>
<!--
2016-04-05 [1d2fe56e4] Fix PL/Python for recursion and interleaved set-returnin
-->
       <para>
        Allow PL/Python functions to call themselves recursively
        via <application>SPI</>, and fix the behavior when multiple
        set-returning PL/Python functions are called within one query
        (Alexey Grishchenko, Tom Lane)
       </para>
      </listitem>

      <listitem>
<!--
2015-11-05 [8c75ad436] Fix memory leaks in PL/Python.
-->
       <para>
        Fix session-lifespan memory leaks in PL/Python (Heikki Linnakangas,
        Haribabu Kommi, Tom Lane)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-02 [287822068] Convert PL/Tcl to use Tcl's "object" interfaces.
2016-03-02 [e2609323e] Make PL/Tcl require Tcl 8.4 or later.
-->
       <para>
        Modernize <application>PL/Tcl</> to use Tcl's <quote>object</>
        <acronym>API</>s instead of simple strings (Jim Nasby, Karl
        Lehenbauer)
       </para>

       <para>
        This can improve performance substantially in some cases.
        Note that <application>PL/Tcl</> now requires Tcl 8.4 or later.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-25 [fb8d2a7f5] In PL/Tcl, make database errors return additional info i
2016-03-25 [cd37bb785] Improve PL/Tcl errorCode facility by providing decoded n
-->
       <para>
        In <application>PL/Tcl</>, make database-reported errors return
        additional information in Tcl's <varname>errorCode</> global
        variable (Jim Nasby, Tom Lane)
       </para>

       <para>
        This feature follows the Tcl convention for returning auxiliary
        data about an error.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-02 [c8c7c93de] Fix PL/Tcl's encoding conversion logic.
-->
       <para>
        Fix <application>PL/Tcl</> to perform encoding conversion between
        the database encoding and <literal>UTF-8</>, which is what Tcl
        expects (Tom Lane)
       </para>

       <para>
        Previously, strings were passed through without conversion,
        leading to misbehavior with non-<literal>ASCII</> characters when
        the database encoding was not <literal>UTF-8</>.
       </para>
      </listitem>

    </itemizedlist>

   </sect3>

   <sect3>
    <title>Client Interfaces</title>

    <itemizedlist>

      <listitem>
<!--
2015-09-05 [0426f349e] Rearrange the handling of error context reports.
This commit is also listed under psql and PL/pgSQL
-->
       <para>
        Introduce a feature in <application>libpq</> whereby the
        <literal>CONTEXT</> field of messages can be suppressed, either
        always or only for non-error messages (Pavel Stehule)
       </para>

       <para>
        The default behavior of <link
        linkend="libpq-pqerrormessage"><function>PQerrorMessage()</></>
        is now to print <literal>CONTEXT</>
        only for errors.  The new function <link
        linkend="libpq-pqseterrorcontextvisibility"><function>PQsetErrorContextVisibility()</></>
        can be used to adjust this.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-03 [e3161b231] Add libpq support for recreating an error message with d
-->
       <para>
        Add support in <application>libpq</> for regenerating an error
        message with a different verbosity level (Alex Shulgin)
       </para>

       <para>
        This supports <application>psql</>'s new <literal>\errverbose</>
        feature, and may be useful for other clients as well.
       </para>
      </listitem>

      <listitem>
<!--
2015-11-27 [40cb21f70] Improve PQhost() to return useful data for default Unix-
-->
       <para>
        Improve <application>libpq</>'s <link
        linkend="libpq-pqhost"><function>PQhost()</></> function to return
        useful data for default Unix-socket connections (Tom Lane)
       </para>

       <para>
        Previously it would return <literal>NULL</> if no explicit host
        specification had been given; now it returns the default socket
        directory path.
       </para>
      </listitem>

      <listitem>
<!--
2016-02-16 [fc1ae7d2e] Change ecpg lexer to accept comments with line breaks in
-->
       <para>
        Fix <application>ecpg</>'s lexer to handle line breaks within
        comments starting on preprocessor directive lines (Michael Meskes)
       </para>
      </listitem>

    </itemizedlist>

   </sect3>

   <sect3>
    <title>Client Applications</title>

    <itemizedlist>

      <listitem>
<!--
2015-09-14 [d02426029] Check existency of table/schema for -t/-n option (pg_dum
-->
       <para>
        Add a <option>--strict-names</> option to <application>pg_dump</>
        and <application>pg_restore</> (Pavel Stehule)
       </para>

       <para>
        This option causes the program to complain if there is no match
        for a <option>-t</option> or <option>-n</option> option, rather
        than silently doing nothing.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-06 [a9f0e8e5a] In pg_dump, use a bitmap to represent what to include
2016-04-06 [d217b2c36] In pg_dump, split "dump" into "dump" and "dump_contains"
2016-04-06 [23f34fa4b] In pg_dump, include pg_catalog and extension ACLs, if ch
2016-05-06 [5d589993c] pg_dump performance and other fixes
2016-05-06 [e1b120a8c] Only issue LOCK TABLE commands when necessary
-->
       <para>
        In <application>pg_dump</>, dump locally-made changes of privilege
        assignments for system objects (Stephen Frost)
       </para>

       <para>
        While it has always been possible for a superuser to change
        the privilege assignments for built-in or extension-created
        objects, such changes were formerly lost in a dump and reload.
        Now, <application>pg_dump</> recognizes and dumps such changes.
        (This works only when dumping from a 9.6 or later server, however.)
       </para>
      </listitem>

      <listitem>
<!--
2016-04-06 [3b3fcc4ee] pg_dump: Add table qualifications to some tags
-->
       <para>
        In <application>pg_dump</>, include the table name in object
        tags for object types that are only uniquely named per-table
        (for example, triggers) (Peter Eisentraut)
       </para>
      </listitem>

    </itemizedlist>

     <sect4>
      <title><xref linkend="APP-PSQL"></title>

      <itemizedlist>

      <listitem>
<!--
2016-04-08 [c09b18f21] Support \crosstabview in psql
-->
       <para>
        Add a <command>\crosstabview</> command that prints the results of
        a query in a cross-tabulated display (Daniel V&eacute;rit&eacute;)
       </para>

       <para>
        In the crosstab display, data values from one query result column
        are placed in a grid whose column and row headers come from other
        query result columns.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-03 [3cc38ca7d] Add psql \errverbose command to see last server error at
-->
       <para>
        Add an <literal>\errverbose</> command that shows the last server
        error at full verbosity (Alex Shulgin)
       </para>

       <para>
        This is useful after getting an unexpected error &mdash; you
        no longer need to adjust the <varname>VERBOSITY</> variable and
        recreate the failure in order to see error fields that are not
        shown by default.
       </para>
      </listitem>

      <listitem>
<!--
2015-07-03 [8eb6407aa] Add psql \ev and \sv commands for editing and showing vi
2016-05-06 [9b66aa006] Fix psql's \ev and \sv commands so that they handle view
-->
       <para>
        Add <literal>\ev</> and <literal>\sv</> commands for editing and
        showing view definitions (Petr Korobeinikov)
       </para>

       <para>
        These are parallel to the existing <literal>\ef</> and
        <literal>\sf</> commands for functions.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-04 [2bbe9112a] Add a \gexec command to psql for evaluation of computed
-->
       <para>
        Add a <command>\gexec</> command that executes a query and
        re-submits the result(s) as new queries (Corey Huinker)
       </para>
      </listitem>

      <listitem>
<!--
2015-10-05 [2145a7660] psql:  allow \pset C in setting the title, matches \C
-->
       <para>
        Allow <literal>\pset C <replaceable>string</></literal>
        to set the table title, for consistency with <literal>\C
        <replaceable>string</></literal> (Bruce Momjian)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-11 [69ab7b9d6] psql: Don't automatically use expanded format when there
-->
       <para>
        In <literal>\pset expanded auto</> mode, do not use expanded
        format for query results with only one column (Andreas Karlsson,
        Robert Haas)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-21 [dea2b5960] Improve header output from psql's \watch command.
2016-06-15 [9901d8ac2] Use strftime("%c") to format timestamps in psql's \watch
-->
       <para>
        Improve the headers output of the <command>\watch</> command
        (Michael Paquier, Tom Lane)
       </para>

       <para>
        Include the <command>\pset title</> string if one has
        been set, and shorten the prefabricated part of the
        header to be <literal><replaceable>timestamp</> (every
        <replaceable>N</>s)</literal>.  Also, the timestamp format now
        obeys <application>psql</>'s locale environment.
       </para>
      </listitem>

      <listitem>
<!--
2015-12-20 [d854118c8] Teach psql's tab completion to consider the entire input
-->
       <para>
        Improve tab-completion logic to consider the entire input query,
        not only the current line (Tom Lane)
       </para>

       <para>
        Previously, breaking a command into multiple lines defeated any
        tab completion rules that needed to see words on earlier lines.
       </para>
      </listitem>

      <listitem>
<!--
2015-08-04 [158e3bc8e] Tab completion for CREATE SEQUENCE.
2015-09-08 [3ae16798f] psql: Generic tab completion support for enum and bool G
2015-09-09 [2f8880704] Improve tab-completion for GRANT and REVOKE.
2015-10-01 [bf4817e4f] Fix incorrect tab-completion for GRANT and REVOKE
2015-10-20 [7c0b49cd0] Tab complete CREATE EXTENSION .. VERSION.
2015-12-25 [8014c44e8] Improve SECURITY LABEL tab completion
2016-01-12 [bc56d5898] psql: Fix CREATE INDEX tab completion
2016-01-12 [b1bfb28b5] psql: Improve CREATE INDEX CONCURRENTLY tab completion
2016-01-16 [4189e3d65] psql: Add completion support for DROP INDEX CONCURRENTLY
2016-01-20 [d0f2f53cd] psql: Add tab completion for COPY with query
2016-01-23 [6ae4c8de0] psql: Improve completion of FDW DDL commands
2016-01-26 [879d71393] Various fixes to REFRESH MATERIALIZED VIEW tab completio
2016-02-01 [89611c4df] Various fixes to "ALTER ... SET/RESET" tab completions
-->
       <para>
        Numerous minor improvements in tab-completion behavior (Peter
        Eisentraut, Vik Fearing, Kevin Grittner, Kyotaro Horiguchi, Jeff
        Janes, Andreas Karlsson, Fujii Masao, Thomas Munro, Masahiko
        Sawada, Pavel Stehule)
       </para>
      </listitem>

      <listitem>
<!--
2015-07-07 [275f05c99] Add psql PROMPT variable showing the pid of the connecte
-->
       <para>
        Add a <literal>PROMPT</> option <literal>%p</> to insert the
        process ID of the connected backend (Julien Rouhaud)
       </para>
      </listitem>

      <listitem>
<!--
2015-09-05 [0426f349e] Rearrange the handling of error context reports.
This commit is also listed under libpq and PL/pgSQL
-->
       <para>
        Introduce a feature whereby the <literal>CONTEXT</> field of
        messages can be suppressed, either always or only for non-error
        messages (Pavel Stehule)
       </para>

       <para>
        Printing <literal>CONTEXT</> only for errors is now the default
        behavior.  This can be changed by setting the special variable
        <varname>SHOW_CONTEXT</varname>.
       </para>
      </listitem>

      <listitem>
<!--
2016-07-11 [a670c24c3] Improve output of psql's \df+ command.
-->
       <para>
        Make <command>\df+</> show function access privileges and
        parallel-safety attributes (Michael Paquier)
       </para>
      </listitem>

      </itemizedlist>

    </sect4>

    <sect4>
     <title><xref linkend="pgbench"></title>

     <itemizedlist>

      <listitem>
<!--
2016-03-20 [68ab8e8ba] SQL commands in pgbench scripts are now ended by semicol
-->
       <para>
        SQL commands in <application>pgbench</> scripts are now ended by
        semicolons, not newlines (Kyotaro Horiguchi, Tom Lane)
       </para>

       <para>
        This change allows SQL commands in scripts to span multiple lines.
        Existing custom scripts will need to be modified to add a semicolon
        at the end of each line if missing.  (Doing so does not break
        the script for use with older versions of <application>pgbench</>.)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-01 [7e137f846] Extend pgbench's expression syntax to support a few buil
2016-03-28 [86c43f4e2] pgbench: Support double constants and functions.
2016-05-05 [7a622b273] Rename pgbench min/max to least/greatest, and fix handli
2016-05-06 [951529948] Improve handling of numeric-valued variables in pgbench.
-->
       <para>
        Support floating-point arithmetic, as well as some <link
        linkend="pgbench-builtin-functions">built-in functions</>, in
        expressions in backslash commands (Fabien Coelho)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-29 [ad9566470] pgbench: Remove \setrandom.
-->
       <para>
        Replace <command>\setrandom</> with built-in functions (Fabien
        Coelho)
       </para>

       <para>
        The new built-in functions include <link
        linkend="pgbench-functions"><function>random()</></>,
        <function>random_exponential()</>, and
        <function>random_gaussian()</>, which perform the same work as
        <command>\setrandom</>, but are easier to use since they can be
        embedded in larger expressions.  Since these additions have made
        <command>\setrandom</> obsolete, remove it.
       </para>
      </listitem>

      <listitem>
<!--
2016-01-27 [8bea3d221] pgbench: improve multi-script support
2016-03-03 [d561f1cae] pgbench: accept unambiguous builtin prefixes for -b
-->
       <para>
        Allow invocation of multiple copies of the built-in scripts,
        not only custom scripts (Fabien Coelho)
       </para>

       <para>
        This is done with the new <option>-b</> switch, which works
        similarly to <option>-f</> for custom scripts.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-19 [7bafffea6] pgbench: Allow changing weights for scripts
-->
       <para>
        Allow changing the selection probabilities (weights) for scripts
        (Fabien Coelho)
       </para>

       <para>
        When multiple scripts are specified, each <application>pgbench</>
        transaction randomly chooses one to execute.  Formerly this was
        always done with uniform probability, but now different selection
        probabilities can be specified for different scripts.
       </para>
      </listitem>

      <listitem>
<!--
2016-02-01 [1d0c3b3f8] pgbench: allow per-script statistics
-->
       <para>
        Collect statistics for each script in a multi-script run (Fabien
        Coelho)
       </para>

       <para>
        This feature adds an intermediate level of detail to existing
        global and per-command statistics printouts.
       </para>
      </listitem>

      <listitem>
<!--
2015-09-16 [1def9063c] pgbench progress with timestamp
-->
       <para>
        Add a <option>--progress-timestamp</> option to report progress
        with Unix epoch timestamps, instead of time since the run started
        (Fabien Coelho)
       </para>
      </listitem>

      <listitem>
<!--
2015-07-03 [ba3deeefb] Lift the limitation that # of clients must be a multiple
-->
       <para>
        Allow the number of client connections (<option>-c</>) to not
        be an exact multiple of the number of threads (<option>-t</>)
        (Fabien Coelho)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-09 [accf7616f] pgbench: When -T is used, don't wait for transactions be
-->
       <para>
        When the <option>-T</> option is used, stop promptly at the end
        of the specified time (Fabien Coelho)
       </para>

       <para>
        Previously, specifying a low transaction rate could cause
        <application>pgbench</> to wait significantly longer than
        specified.
       </para>
      </listitem>

     </itemizedlist>

    </sect4>

   </sect3>

   <sect3>
    <title>Server Applications</title>

    <itemizedlist>

      <listitem>
<!--
2015-12-17 [66d947b9d] Adjust behavior of single-user -j mode for better initdb
-->
       <para>
        Improve error reporting during <application>initdb</>'s
        post-bootstrap phase (Tom Lane)
       </para>

       <para>
        Previously, an error here led to reporting the entire input
        file as the <quote>failing query</>; now just the current
        query is reported.  To get the desired behavior, queries in
        <application>initdb</>'s input files must be separated by blank
        lines.
       </para>
      </listitem>

      <listitem>
<!--
2015-12-17 [c4a8812cf] Use just one standalone-backend session for initdb's pos
-->
       <para>
        Speed up <application>initdb</> by using just one
        standalone-backend session for all the post-bootstrap steps
        (Tom Lane)
       </para>
      </listitem>

      <listitem>
<!--
2015-12-01 [e50cda784] Use pg_rewind when target timeline was switched
-->
       <para>
        Improve <application>pg_rewind</> so that it can work when the
        target timeline changes (Alexander Korotkov)
       </para>

       <para>
        This allows, for example, rewinding a promoted standby back to
        some state of the old master's timeline.
       </para>
      </listitem>

    </itemizedlist>

   </sect3>

   <sect3>
    <title>Source Code</title>

     <itemizedlist>

      <listitem>
<!--
2015-07-02 [726117243] Remove obsolete heap_formtuple/modifytuple/deformtuple f
-->
       <para>
        Remove obsolete
        <function>heap_formtuple</>/<function>heap_modifytuple</>/<function>heap_deformtuple</>
        functions (Peter Geoghegan)
       </para>
      </listitem>

      <listitem>
<!--
2015-08-05 [de6fd1c89] Rely on inline functions even if that causes warnings in
-->
       <para>
        Unconditionally use <literal>static inline</> functions in header
        files (Andres Freund)
       </para>

       <para>
        This may result in warnings and/or wasted code space with very
        old compilers, but the notational improvement seems worth it.
       </para>
      </listitem>

      <listitem>
<!--
2015-07-29 [13d856e17] Make TAP tests work on Windows.
2015-12-02 [1caef31d9] Refactor Perl test code
2015-12-07 [9821492ee] Cleanup some problems in new Perl test code
2016-03-03 [2c83f435a] Rework PostgresNode's psql method
2016-02-26 [49148645f] Add a test framework for recovery
2016-02-26 [74d58425c] Apply last revision of recovery patch
2016-05-06 [6bd356c33] Add TAP tests for pg_dump
-->
       <para>
        Improve <application>TAP</> testing infrastructure (Michael
        Paquier, Craig Ringer, &Aacute;lvaro Herrera, Stephen Frost)
       </para>

       <para>
        Notably, it is now possible to test recovery scenarios using
        this infrastructure.
       </para>
      </listitem>

      <listitem>
<!--
2015-09-11 [aa65de042] When trace_lwlocks is used, identify individual lwlocks
-->
       <para>
        Make <varname>trace_lwlocks</> identify individual locks by name
        (Robert Haas)
       </para>
      </listitem>

      <listitem>
<!--
2015-12-19 [d37b816dc] Adopt a more compact, less error-prone notation for tab
2016-01-04 [9b181b036] In psql's tab completion, change most TailMatches patter
2016-01-05 [4f18010af] Convert psql's tab completion for backslash commands to
-->
       <para>
        Improve <application>psql</>'s tab-completion code infrastructure
        (Thomas Munro, Michael Paquier)
       </para>

       <para>
        Tab-completion rules are now considerably easier to write, and
        more compact.
       </para>
      </listitem>

      <listitem>
<!--
2016-01-05 [efa318bcf] Make pg_shseclabel available in early backend startup
-->
       <para>
        Nail the <structname>pg_shseclabel</> system catalog into cache,
        so that it is available for access during connection authentication
        (Adam Brightwell)
       </para>

       <para>
        The core code does not use this catalog for authentication,
        but extensions might wish to consult it.
       </para>
      </listitem>

      <listitem>
<!--
2016-01-17 [65c5fcd35] Restructure index access method API to hide most of it a
2016-01-21 [be44ed27b] Improve index AMs' opclass validation procedures.
-->
       <para>
        Restructure index access method <acronym>API</> to hide most of
        it at the <application>C</> level (Alexander Korotkov)
       </para>

       <para>
        This change modernizes the index <acronym>AM API</> to look more
        like the designs we have adopted for foreign data wrappers and
        tablesample handlers.  This simplifies the <application>C</> code
        and should make it more feasible to define index access methods in
        installable extensions.  A consequence is that most of the columns
        of the <structname>pg_am</> system catalog have disappeared.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-06 [6c268df12] Add new catalog called pg_init_privs
-->
       <para>
        Add <structname>pg_init_privs</> system catalog to hold original
        privileges of <application>initdb</>-created and extension-created
        objects (Stephen Frost)
       </para>

       <para>
        This infrastructure allows <application>pg_dump</> to dump changes
        that an installation may have made in privileges attached to
        system objects.  Formerly, such changes would be lost in a dump
        and reload, but now they are preserved.
       </para>
      </listitem>

      <listitem>
<!--
2016-02-04 [c1772ad92] Change the way that LWLocks for extensions are allocated
-->
       <para>
        Change the way that extensions allocate custom <literal>LWLocks</>
        (Amit Kapila, Robert Haas)
       </para>

       <para>
        The <function>RequestAddinLWLocks()</> function is removed,
        and replaced by <function>RequestNamedLWLockTranche()</>.
        This allows better identification of custom <literal>LWLocks</>,
        and is less error-prone.
       </para>
      </listitem>

      <listitem>
<!--
2016-02-11 [38f8bdcac] Modify the isolation tester so that multiple sessions ca
-->
       <para>
        Improve the isolation tester to allow multiple sessions to wait
        concurrently, allowing testing of deadlock scenarios (Robert Haas)
       </para>
      </listitem>

      <listitem>
<!--
2016-02-12 [bcac23de7] Introduce extensible node types.
-->
       <para>
        Introduce extensible node types (KaiGai Kohei)
       </para>

       <para>
        This change allows <application>FDW</>s or custom scan providers
        to store data in a plan tree in a more convenient format than
        was previously possible.
       </para>
      </listitem>

      <listitem>
<!--
2015-08-11 [68fa28f77] Postpone extParam/allParam calculations until the very e
2016-01-07 [c44d01383] Delay creation of subplan tlist until after create_plan(
2016-02-18 [19a541143] Add an explicit representation of the output targetlist
2016-03-07 [3fc6e2d7f] Make the upper part of the planner work by generating an
2016-07-01 [5ce5e4a12] Set consider_parallel correctly for upper planner rels.
2016-07-01 [9e703987a] Rethink the GetForeignUpperPaths API (again).
-->
       <para>
        Make the planner deal with post-scan/join query steps by generating
        and comparing <literal>Paths</>, replacing a lot of ad-hoc logic
        (Tom Lane)
       </para>

       <para>
        This change provides only marginal user-visible improvements today,
        but it enables future work on a lot of upper-planner improvements
        that were impractical to tackle using the old code structure.
       </para>
      </listitem>

      <listitem>
<!--
2016-01-20 [a7de3dc5c] Support multi-stage aggregation.
2016-06-22 [f8ace5477] Fix type-safety problem with parallel aggregate serial/d
2016-06-26 [19e972d55] Rethink node-level representation of partial-aggregation
-->
       <para>
        Support partial aggregation (David Rowley, Simon Riggs)
       </para>

       <para>
        This change allows the computation of an aggregate function to be
        split into separate parts, for example so that parallel worker
        processes can cooperate on computing an aggregate.  In future
        it might allow aggregation across local and remote data to occur
        partially on the remote end.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-09 [b6fb6471f] Add a generic command progress reporting facility.
-->
       <para>
        Add a generic command progress reporting facility (Vinayak Pokale,
        Rahila Syed, Amit Langote, Robert Haas)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-18 [27199058d] Convert psql's flex lexer to be re-entrant, and make it
2016-03-19 [0ea9efbe9] Split psql's lexer into two separate .l files for SQL an
2016-03-20 [b6afae71a] Use %option bison-bridge in psql/pgbench lexers.
2016-03-24 [588d963b0] Create src/fe_utils/, and move stuff into there from pg_
2016-03-24 [d65bea26a] Move psql's print.c and mbprint.c into src/fe_utils.
2016-03-24 [c1156411a] Move psql's psqlscan.l into src/fe_utils.
-->
       <para>
        Separate out <application>psql</>'s <application>flex</> lexer to
        make it usable by other client programs (Tom Lane, Kyotaro
        Horiguchi)
       </para>

       <para>
        This eliminates code duplication for programs that need to be able
        to parse SQL commands well enough to identify command boundaries.
        Doing that in full generality is more painful than one could
        wish, and up to now only <application>psql</> has really gotten
        it right among our supported client programs.
       </para>

       <para>
        A new source-code subdirectory <filename>src/fe_utils/</> has
        been created to hold this and other code that is shared across
        our client programs.  Formerly such sharing was accomplished by
        symbolic linking or copying source files at build time, which
        was ugly and required duplicate compilation.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-21 [98a64d0bd] Introduce WaitEventSet API.
-->
       <para>
        Introduce <literal>WaitEventSet</> <acronym>API</> to allow
        efficient waiting for event sets that usually do not change from
        one wait to the next (Andres Freund, Amit Kapila)
       </para>
      </listitem>

      <listitem>
<!--
2016-04-01 [65578341a] Add Generic WAL interface
-->
       <para>
        Add a generic interface for writing <acronym>WAL</> records
        (Alexander Korotkov, Petr Jel&iacute;nek, Markus Nullmeier)
       </para>

       <para>
        This change allows extensions to write <acronym>WAL</> records for
        changes to pages using a standard layout.  The problem of needing to
        replay <acronym>WAL</> without access to the extension is solved by
        having generic replay code.  This allows extensions to implement,
        for example, index access methods and have <acronym>WAL</>
        support for them.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-06 [3fe3511d0] Generic Messages for Logical Decoding
-->
       <para>
        Support generic <acronym>WAL</> messages for logical decoding
        (Petr Jel&iacute;nek, Andres Freund)
       </para>

       <para>
        This feature allows extensions to insert data into the
        <acronym>WAL</> stream that can be read by logical-decoding
        plugins, but is not connected to physical data restoration.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-30 [ccd6eb49a] Introduce traversalValue for SP-GiST scan
2016-03-30 [87545f541] Use traversalValue in SP-GiST range opclass.
-->
       <para>
        Allow SP-GiST operator classes to store an arbitrary
        <quote>traversal value</> while descending the index (Alexander
        Lebedev, Teodor Sigaev)
       </para>

       <para>
        This is somewhat like the <quote>reconstructed value</>, but it
        could be any arbitrary chunk of data, it need not be of the same
        data type as the indexed column.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-04 [66229ac00] Introduce a LOG_SERVER_ONLY ereport level, which is neve
-->
       <para>
        Introduce a <literal>LOG_SERVER_ONLY</> message level for
        <function>ereport()</> (David Steele)
       </para>

       <para>
        This level acts like <literal>LOG</> except that the message is
        never sent to the client.  It is meant for use in auditing and
        similar applications.
       </para>
      </listitem>

      <listitem>
<!--
2016-07-01 [548af97fc] Provide and use a makefile target to build all generated
-->
       <para>
        Provide a <filename>Makefile</> target to build all generated
        headers (Michael Paquier, Tom Lane)
       </para>

       <para>
        <literal>submake-generated-headers</> can now be invoked to ensure
        that generated backend header files are up-to-date.  This is
        useful in subdirectories that might be built <quote>standalone</>.
       </para>
      </listitem>

     </itemizedlist>

   </sect3>

   <sect3>
    <title>Additional Modules</title>

    <itemizedlist>

      <listitem>
<!--
2016-03-11 [92f03fe76] Allow setting sample ratio for auto_explain
2016-03-13 [7a8d87483] Rename auto_explain.sample_ratio to sample_rate
-->
       <para>
        Add configuration parameter <literal>auto_explain.sample_rate</>
        to allow <filename>contrib/auto_explain</> to capture just a
        configurable fraction of all queries (Craig Ringer, Julien Rouhaud)
       </para>

       <para>
        This allows reduction of overhead for heavy query traffic, while
        still getting useful information on average.
       </para>
      </listitem>

      <listitem>
<!--
2016-04-01 [9ee014fc8] Bloom index contrib module
-->
       <para>
        Add <filename>contrib/bloom</> module that implements an index
        access method based on Bloom filtering (Teodor Sigaev, Alexander
        Korotkov)
       </para>

       <para>
        This is primarily a proof-of-concept for non-core index access
        methods, but it could be useful in its own right for queries that
        search many columns.
       </para>
      </listitem>

      <listitem>
<!--
2015-12-18 [33bd250f6] Cube extension kNN support
2015-12-28 [81ee726d8] Code and docs review for cube kNN support.
-->
       <para>
        In <filename>contrib/cube</>, introduce distance operators for
        cubes, and support kNN-style searches in GiST indexes on cube
        columns (Stas Kelvich)
       </para>
      </listitem>

      <listitem>
<!--
2016-02-03 [41d2c081c] Make hstore_to_jsonb_loose match hstore_to_json_loose on
-->
       <para>
        Make <filename>contrib/hstore</>'s <link
        linkend="hstore-func-table"><function>hstore_to_jsonb_loose()</></>
        and <function>hstore_to_json_loose()</> functions agree on what
        is a number (Tom Lane)
       </para>

       <para>
        Previously, <function>hstore_to_jsonb_loose()</> would convert
        numeric-looking strings to <acronym>JSON</> numbers, rather than
        strings, even if they did not exactly match the <acronym>JSON</>
        syntax specification for numbers.  This was inconsistent with
        <function>hstore_to_json_loose()</>, so tighten the test to match
        the <acronym>JSON</> syntax.
       </para>
      </listitem>

      <listitem>
<!--
2015-07-21 [c6fbe6d6f] Add selectivity estimation functions for intarray operat
-->
       <para>
        Add selectivity estimation functions for
        <filename>contrib/intarray</> operators to improve plans for
        queries using those operators (Yury Zhuravlev, Alexander Korotkov)
       </para>
      </listitem>

      <listitem>
<!--
2015-11-25 [d6061f83a] Improve pageinspect module
-->
       <para>
        Make <link
        linkend="pageinspect"><filename>contrib/pageinspect</></>'s
        <function>heap_page_items()</> function show the raw data in each
        tuple, and add new functions <function>tuple_data_split()</> and
        <function>heap_page_item_attrs()</> for inspection of individual
        tuple fields (Nikolay Shaplov)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-09 [188f359d3] pgcrypto: support changing S2K iteration count
-->
       <para>
        Add an optional <literal>S2K</> iteration count parameter to
        <link linkend="pgcrypto"><filename>contrib/pgcrypto</></>'s
        <function>pgp_sym_encrypt()</> function (Jeff Janes)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-16 [f576b17cd] Add word_similarity to pg_trgm contrib module.
-->
       <para>
        Add support for <quote>word similarity</> to
        <filename>contrib/pg_trgm</> (Alexander Korotkov, Artur Zakirov)
       </para>

       <para>
        These functions and operators measure the similarity between one
        string and the most similar single word of another string.
       </para>
      </listitem>

      <listitem>
<!--
2016-03-16 [5871b8848] GUC variable pg_trgm.similarity_threshold insead of set_
2016-06-20 [9c852566a] Fix comparison of similarity to threshold in GIST trigra
-->
       <para>
        Add configuration parameter
        <varname>pg_trgm.similarity_threshold</> for <link
        linkend="pgtrgm"><filename>contrib/pg_trgm</></>'s similarity
        threshold (Artur Zakirov)
       </para>

       <para>
        This threshold has always been configurable, but formerly it was
        controlled by special-purpose functions <function>set_limit()</>
        and <function>show_limit()</>.  Those are now deprecated.
       </para>
      </listitem>

      <listitem>
<!--
2015-07-20 [97f301464] This supports the triconsistent function for pg_trgm GIN
-->
       <para>
        Improve <filename>contrib/pg_trgm</>'s GIN operator class to
        speed up index searches in which both common and rare keys appear
        (Jeff Janes)
       </para>
      </listitem>

      <listitem>
<!--
2015-12-25 [25bfa7efd] Improve the gin index scan performance in pg_trgm.
-->
       <para>
        Improve performance of similarity searches in
        <filename>contrib/pg_trgm</> GIN indexes (Christophe Fornaroli)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-08 [ba0a198fb] Add pg_visibility contrib module.
2016-06-17 [71d05a2c7] pg_visibility: Add pg_truncate_visibility_map function.
-->
       <para>
        Add <filename>contrib/pg_visibility</> module to allow examining
        table visibility maps (Robert Haas)
       </para>
      </listitem>

      <listitem>
<!--
2015-09-07 [49124613f] contrib/sslinfo: add ssl_extension_info SRF
-->
       <para>
        Add <link linkend="sslinfo"><function>ssl_extension_info()</></>
        function to <filename>contrib/sslinfo</>, to print information
        about <acronym>SSL</> extensions present in the <literal>X509</>
        certificate used for the current connection (Dmitry Voronin)
       </para>
      </listitem>

    </itemizedlist>

    <sect4>
     <title><filename>postgres_fdw</></title>

     <itemizedlist>

      <listitem>
<!--
2015-11-03 [d89494166] Allow postgres_fdw to ship extension funcs/operators for
-->
       <para>
        Allow extension-provided operators and functions to be sent for
        remote execution, if the extension is whitelisted in the foreign
        server's options (Paul Ramsey)
       </para>

       <para>
        Users can enable this feature when the extension is known to exist
        in a compatible version in the remote database.  It allows more
        efficient execution of queries involving extension operators.
       </para>
      </listitem>

      <listitem>
<!--
2015-11-03 [f18c944b6] postgres_fdw: Add ORDER BY to some remote SQL queries.
2015-12-22 [ccd8f9792] postgres_fdw: Consider requesting sorted data so we can
-->
       <para>
        Consider performing sorts on the remote server (Ashutosh Bapat)
       </para>
      </listitem>

      <listitem>
<!--
2016-02-09 [e4106b252] postgres_fdw: Push down joins to remote servers.
2016-03-09 [aa09cd242] postgres_fdw: Consider foreign joining and foreign sorti
-->
       <para>
        Consider performing joins on the remote server (Shigeru Hanada,
        Ashutosh Bapat)
       </para>
      </listitem>

      <listitem>
<!--
2016-03-18 [0bf3ae88a] Directly modify foreign tables.
-->
       <para>
        When feasible, perform <command>UPDATE</> or <command>DELETE</>
        entirely on the remote server (Etsuro Fujita)
       </para>

       <para>
        Formerly, this involved sending a <command>SELECT FOR UPDATE</>
        command and then updating or deleting the selected rows one-by-one.
        While that is still necessary if the operation requires any local
        processing, it can now be done remotely if all elements of the
        query are safe to send to the remote server.
       </para>
      </listitem>

      <listitem>
<!--
2016-02-03 [dc203dc3a] postgres_fdw: Allow fetch_size to be set per-table or pe
-->
       <para>
        Allow the fetch size to be set as a server or table option
        (Corey Huinker)
       </para>

       <para>
        Formerly, <filename>postgres_fdw</> always fetched 100 rows at
        a time from remote queries; now that behavior is configurable.
       </para>
      </listitem>

      <listitem>
<!--
2016-01-28 [96198d94c] Avoid multiple foreign server connections when all use s
-->
       <para>
        Use a single foreign-server connection for local user IDs that
        all map to the same remote user (Ashutosh Bapat)
       </para>
      </listitem>

      <listitem>
<!--
2016-04-21 [f039eaac7] Allow queries submitted by postgres_fdw to be canceled.
2016-05-16 [1b812afb0] Fix multiple problems in postgres_fdw query cancellation
-->
       <para>
        Transmit query cancellation requests to the remote server
        (Michael Paquier)
       </para>

       <para>
        Previously, a local query cancellation request did not cause an
        already-sent remote query to terminate early.
       </para>
      </listitem>

     </itemizedlist>

    </sect4>

   </sect3>

  </sect2>

 </sect1>
