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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>9.26. System Administration Functions</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="functions-info.html" title="9.25. System Information Functions and Operators" /><link rel="next" href="functions-trigger.html" title="9.27. Trigger Functions" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">9.26. System Administration Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="functions-info.html" title="9.25. System Information Functions and Operators">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><th width="60%" align="center">Chapter 9. Functions and Operators</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="functions-trigger.html" title="9.27. Trigger Functions">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="FUNCTIONS-ADMIN"><div class="titlepage"><div><div><h2 class="title" style="clear: both">9.26. System Administration Functions</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-ADMIN-SET">9.26.1. Configuration Settings Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-ADMIN-SIGNAL">9.26.2. Server Signaling Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-ADMIN-BACKUP">9.26.3. Backup Control Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-RECOVERY-CONTROL">9.26.4. Recovery Control Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-SNAPSHOT-SYNCHRONIZATION">9.26.5. Snapshot Synchronization Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-REPLICATION">9.26.6. Replication Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-ADMIN-DBOBJECT">9.26.7. Database Object Management Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-ADMIN-INDEX">9.26.8. Index Maintenance Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-ADMIN-GENFILE">9.26.9. Generic File Access Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-ADVISORY-LOCKS">9.26.10. Advisory Lock Functions</a></span></dt></dl></div><p>

  3.     The functions described in this section are used to control and

  4.     monitor a <span class="productname">PostgreSQL</span> installation.

  5.    </p><div class="sect2" id="FUNCTIONS-ADMIN-SET"><div class="titlepage"><div><div><h3 class="title">9.26.1. Configuration Settings Functions</h3></div></div></div><p>

  6.     <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-SET-TABLE" title="Table 9.82. Configuration Settings Functions">Table 9.82</a> shows the functions

  7.     available to query and alter run-time configuration parameters.

  8.    </p><div class="table" id="FUNCTIONS-ADMIN-SET-TABLE"><p class="title"><strong>Table 9.82. Configuration Settings Functions</strong></p><div class="table-contents"><table class="table" summary="Configuration Settings Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>

  9.         <a id="id-1.5.8.31.3.3.2.2.1.1.1" class="indexterm"></a>

  10.         <code class="literal"><code class="function">current_setting(<em class="parameter"><code>setting_name</code></em> [, <em class="parameter"><code>missing_ok</code></em> ])</code></code>

  11.        </td><td><code class="type">text</code></td><td>get current value of setting</td></tr><tr><td>

  12.         <a id="id-1.5.8.31.3.3.2.2.2.1.1" class="indexterm"></a>

  13.         <code class="literal"><code class="function">set_config(<em class="parameter"><code>setting_name</code></em>,

  14.                              <em class="parameter"><code>new_value</code></em>,

  15.                              <em class="parameter"><code>is_local</code></em>)</code></code>

  16.        </td><td><code class="type">text</code></td><td>set parameter and return new value</td></tr></tbody></table></div></div><br class="table-break" /><a id="id-1.5.8.31.3.4" class="indexterm"></a><a id="id-1.5.8.31.3.5" class="indexterm"></a><a id="id-1.5.8.31.3.6" class="indexterm"></a><p>

  17.     The function <code class="function">current_setting</code> yields the

  18.     current value of the setting <em class="parameter"><code>setting_name</code></em>.

  19.     It corresponds to the <acronym class="acronym">SQL</acronym> command

  20.     <code class="command">SHOW</code>.  An example:

  21. </p><pre class="programlisting">

  22. SELECT current_setting('datestyle');

  23. 

  24.  current_setting

  25. -----------------

  26.  ISO, MDY

  27. (1 row)

  28. </pre><p>

  29. 

  30.     If there is no setting named <em class="parameter"><code>setting_name</code></em>,

  31.     <code class="function">current_setting</code> throws an error

  32.     unless <em class="parameter"><code>missing_ok</code></em> is supplied and is

  33.     <code class="literal">true</code>.

  34.    </p><p>

  35.     <code class="function">set_config</code> sets the parameter

  36.     <em class="parameter"><code>setting_name</code></em> to

  37.     <em class="parameter"><code>new_value</code></em>.  If

  38.     <em class="parameter"><code>is_local</code></em> is <code class="literal">true</code>, the

  39.     new value will only apply to the current transaction. If you want

  40.     the new value to apply for the current session, use

  41.     <code class="literal">false</code> instead. The function corresponds to the

  42.     SQL command <code class="command">SET</code>. An example:

  43. </p><pre class="programlisting">

  44. SELECT set_config('log_statement_stats', 'off', false);

  45. 

  46.  set_config

  47. ------------

  48.  off

  49. (1 row)

  50. </pre><p>

  51.    </p></div><div class="sect2" id="FUNCTIONS-ADMIN-SIGNAL"><div class="titlepage"><div><div><h3 class="title">9.26.2. Server Signaling Functions</h3></div></div></div><a id="id-1.5.8.31.4.2" class="indexterm"></a><a id="id-1.5.8.31.4.3" class="indexterm"></a><a id="id-1.5.8.31.4.4" class="indexterm"></a><a id="id-1.5.8.31.4.5" class="indexterm"></a><a id="id-1.5.8.31.4.6" class="indexterm"></a><p>

  52.     The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-SIGNAL-TABLE" title="Table 9.83. Server Signaling Functions">Table 9.83</a> send control signals to

  53.     other server processes.  Use of these functions is restricted to

  54.     superusers by default but access may be granted to others using

  55.     <code class="command">GRANT</code>, with noted exceptions.

  56.    </p><div class="table" id="FUNCTIONS-ADMIN-SIGNAL-TABLE"><p class="title"><strong>Table 9.83. Server Signaling Functions</strong></p><div class="table-contents"><table class="table" summary="Server Signaling Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>

  57.         <code class="literal"><code class="function">pg_cancel_backend(<em class="parameter"><code>pid</code></em> <code class="type">int</code>)</code></code>

  58.         </td><td><code class="type">boolean</code></td><td>Cancel a backend's current query.  This is also allowed if the

  59.         calling role is a member of the role whose backend is being canceled or

  60.         the calling role has been granted <code class="literal">pg_signal_backend</code>,

  61.         however only superusers can cancel superuser backends.

  62.         </td></tr><tr><td>

  63.         <code class="literal"><code class="function">pg_reload_conf()</code></code>

  64.         </td><td><code class="type">boolean</code></td><td>Cause server processes to reload their configuration files</td></tr><tr><td>

  65.         <code class="literal"><code class="function">pg_rotate_logfile()</code></code>

  66.         </td><td><code class="type">boolean</code></td><td>Rotate server's log file</td></tr><tr><td>

  67.         <code class="literal"><code class="function">pg_terminate_backend(<em class="parameter"><code>pid</code></em> <code class="type">int</code>)</code></code>

  68.         </td><td><code class="type">boolean</code></td><td>Terminate a backend.  This is also allowed if the calling role

  69.         is a member of the role whose backend is being terminated or the

  70.         calling role has been granted <code class="literal">pg_signal_backend</code>,

  71.         however only superusers can terminate superuser backends.

  72.        </td></tr></tbody></table></div></div><br class="table-break" /><p>

  73.     Each of these functions returns <code class="literal">true</code> if

  74.     successful and <code class="literal">false</code> otherwise.

  75.    </p><p>

  76.     <code class="function">pg_cancel_backend</code> and <code class="function">pg_terminate_backend</code>

  77.     send signals (<span class="systemitem">SIGINT</span> or <span class="systemitem">SIGTERM</span>

  78.     respectively) to backend processes identified by process ID.

  79.     The process ID of an active backend can be found from

  80.     the <code class="structfield">pid</code> column of the

  81.     <code class="structname">pg_stat_activity</code> view, or by listing the

  82.     <code class="command">postgres</code> processes on the server (using

  83.     <span class="application">ps</span> on Unix or the <span class="application">Task

  84.     Manager</span> on <span class="productname">Windows</span>).

  85.     The role of an active backend can be found from the

  86.     <code class="structfield">usename</code> column of the

  87.     <code class="structname">pg_stat_activity</code> view.

  88.    </p><p>

  89.     <code class="function">pg_reload_conf</code> sends a <span class="systemitem">SIGHUP</span> signal

  90.     to the server, causing configuration files

  91.     to be reloaded by all server processes.

  92.    </p><p>

  93.     <code class="function">pg_rotate_logfile</code> signals the log-file manager to switch

  94.     to a new output file immediately.  This works only when the built-in

  95.     log collector is running, since otherwise there is no log-file manager

  96.     subprocess.

  97.    </p></div><div class="sect2" id="FUNCTIONS-ADMIN-BACKUP"><div class="titlepage"><div><div><h3 class="title">9.26.3. Backup Control Functions</h3></div></div></div><a id="id-1.5.8.31.5.2" class="indexterm"></a><a id="id-1.5.8.31.5.3" class="indexterm"></a><a id="id-1.5.8.31.5.4" class="indexterm"></a><a id="id-1.5.8.31.5.5" class="indexterm"></a><a id="id-1.5.8.31.5.6" class="indexterm"></a><a id="id-1.5.8.31.5.7" class="indexterm"></a><a id="id-1.5.8.31.5.8" class="indexterm"></a><a id="id-1.5.8.31.5.9" class="indexterm"></a><a id="id-1.5.8.31.5.10" class="indexterm"></a><a id="id-1.5.8.31.5.11" class="indexterm"></a><a id="id-1.5.8.31.5.12" class="indexterm"></a><a id="id-1.5.8.31.5.13" class="indexterm"></a><a id="id-1.5.8.31.5.14" class="indexterm"></a><p>

  98.     The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-BACKUP-TABLE" title="Table 9.84. Backup Control Functions">Table 9.84</a> assist in making on-line backups.

  99.     These functions cannot be executed during recovery (except

  100.     non-exclusive <code class="function">pg_start_backup</code>,

  101.     non-exclusive <code class="function">pg_stop_backup</code>,

  102.     <code class="function">pg_is_in_backup</code>, <code class="function">pg_backup_start_time</code>

  103.     and <code class="function">pg_wal_lsn_diff</code>).

  104.    </p><div class="table" id="FUNCTIONS-ADMIN-BACKUP-TABLE"><p class="title"><strong>Table 9.84. Backup Control Functions</strong></p><div class="table-contents"><table class="table" summary="Backup Control Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>

  105.         <code class="literal"><code class="function">pg_create_restore_point(<em class="parameter"><code>name</code></em> <code class="type">text</code>)</code></code>

  106.         </td><td><code class="type">pg_lsn</code></td><td>Create a named point for performing restore (restricted to superusers by default, but other users can be granted EXECUTE to run the function)</td></tr><tr><td>

  107.         <code class="literal"><code class="function">pg_current_wal_flush_lsn()</code></code>

  108.         </td><td><code class="type">pg_lsn</code></td><td>Get current write-ahead log flush location</td></tr><tr><td>

  109.         <code class="literal"><code class="function">pg_current_wal_insert_lsn()</code></code>

  110.         </td><td><code class="type">pg_lsn</code></td><td>Get current write-ahead log insert location</td></tr><tr><td>

  111.         <code class="literal"><code class="function">pg_current_wal_lsn()</code></code>

  112.         </td><td><code class="type">pg_lsn</code></td><td>Get current write-ahead log write location</td></tr><tr><td>

  113.         <code class="literal"><code class="function">pg_start_backup(<em class="parameter"><code>label</code></em> <code class="type">text</code> [<span class="optional">, <em class="parameter"><code>fast</code></em> <code class="type">boolean</code> [<span class="optional">, <em class="parameter"><code>exclusive</code></em> <code class="type">boolean</code> </span>]</span>])</code></code>

  114.         </td><td><code class="type">pg_lsn</code></td><td>Prepare for performing on-line backup (restricted to superusers by default, but other users can be granted EXECUTE to run the function)</td></tr><tr><td>

  115.         <code class="literal"><code class="function">pg_stop_backup()</code></code>

  116.         </td><td><code class="type">pg_lsn</code></td><td>Finish performing exclusive on-line backup (restricted to superusers by default, but other users can be granted EXECUTE to run the function)</td></tr><tr><td>

  117.         <code class="literal"><code class="function">pg_stop_backup(<em class="parameter"><code>exclusive</code></em> <code class="type">boolean</code> [<span class="optional">, <em class="parameter"><code>wait_for_archive</code></em> <code class="type">boolean</code> </span>])</code></code>

  118.         </td><td><code class="type">setof record</code></td><td>Finish performing exclusive or non-exclusive on-line backup (restricted to superusers by default, but other users can be granted EXECUTE to run the function)</td></tr><tr><td>

  119.         <code class="literal"><code class="function">pg_is_in_backup()</code></code>

  120.         </td><td><code class="type">bool</code></td><td>True if an on-line exclusive backup is still in progress.</td></tr><tr><td>

  121.         <code class="literal"><code class="function">pg_backup_start_time()</code></code>

  122.         </td><td><code class="type">timestamp with time zone</code></td><td>Get start time of an on-line exclusive backup in progress.</td></tr><tr><td>

  123.         <code class="literal"><code class="function">pg_switch_wal()</code></code>

  124.         </td><td><code class="type">pg_lsn</code></td><td>Force switch to a new write-ahead log file (restricted to superusers by default, but other users can be granted EXECUTE to run the function)</td></tr><tr><td>

  125.         <code class="literal"><code class="function">pg_walfile_name(<em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>)</code></code>

  126.         </td><td><code class="type">text</code></td><td>Convert write-ahead log location to file name</td></tr><tr><td>

  127.         <code class="literal"><code class="function">pg_walfile_name_offset(<em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>)</code></code>

  128.         </td><td><code class="type">text</code>, <code class="type">integer</code></td><td>Convert write-ahead log location to file name and decimal byte offset within file</td></tr><tr><td>

  129.         <code class="literal"><code class="function">pg_wal_lsn_diff(<em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>, <em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>)</code></code>

  130.        </td><td><code class="type">numeric</code></td><td>Calculate the difference between two write-ahead log locations</td></tr></tbody></table></div></div><br class="table-break" /><p>

  131.     <code class="function">pg_start_backup</code> accepts an arbitrary user-defined label for

  132.     the backup.  (Typically this would be the name under which the backup dump

  133.     file will be stored.) When used in exclusive mode, the function writes a

  134.     backup label file (<code class="filename">backup_label</code>) and, if there are any links

  135.     in the <code class="filename">pg_tblspc/</code> directory, a tablespace map file

  136.     (<code class="filename">tablespace_map</code>) into the database cluster's data directory,

  137.     performs a checkpoint, and then returns the backup's starting write-ahead

  138.     log location as text.  The user can ignore this result value, but it is

  139.     provided in case it is useful. When used in non-exclusive mode, the

  140.     contents of these files are instead returned by the

  141.     <code class="function">pg_stop_backup</code> function, and should be written to the backup

  142.     by the caller.

  143. 

  144. </p><pre class="programlisting">

  145. postgres=# select pg_start_backup('label_goes_here');

  146.  pg_start_backup

  147. -----------------

  148.  0/D4445B8

  149. (1 row)

  150. </pre><p>

  151.     There is an optional second parameter of type <code class="type">boolean</code>.  If <code class="literal">true</code>,

  152.     it specifies executing <code class="function">pg_start_backup</code> as quickly as

  153.     possible.  This forces an immediate checkpoint which will cause a

  154.     spike in I/O operations, slowing any concurrently executing queries.

  155.    </p><p>

  156.     In an exclusive backup, <code class="function">pg_stop_backup</code> removes the label file

  157.     and, if it exists, the <code class="filename">tablespace_map</code> file created by

  158.     <code class="function">pg_start_backup</code>. In a non-exclusive backup, the contents of

  159.     the <code class="filename">backup_label</code> and <code class="filename">tablespace_map</code> are returned

  160.     in the result of the function, and should be written to files in the

  161.     backup (and not in the data directory).  There is an optional second

  162.     parameter of type <code class="type">boolean</code>.  If false, the <code class="function">pg_stop_backup</code>

  163.     will return immediately after the backup is completed without waiting for

  164.     WAL to be archived.  This behavior is only useful for backup

  165.     software which independently monitors WAL archiving. Otherwise, WAL

  166.     required to make the backup consistent might be missing and make the backup

  167.     useless.  When this parameter is set to true, <code class="function">pg_stop_backup</code>

  168.     will wait for WAL to be archived when archiving is enabled; on the standby,

  169.     this means that it will wait only when <code class="varname">archive_mode = always</code>.

  170.     If write activity on the primary is low, it may be useful to run

  171.     <code class="function">pg_switch_wal</code> on the primary in order to trigger

  172.     an immediate segment switch.

  173.    </p><p>

  174.     When executed on a primary, the function also creates a backup history file

  175.     in the write-ahead log

  176.     archive area. The history file includes the label given to

  177.     <code class="function">pg_start_backup</code>, the starting and ending write-ahead log locations for

  178.     the backup, and the starting and ending times of the backup.  The return

  179.     value is the backup's ending write-ahead log location (which again

  180.     can be ignored).  After recording the ending location, the current

  181.     write-ahead log insertion

  182.     point is automatically advanced to the next write-ahead log file, so that the

  183.     ending write-ahead log file can be archived immediately to complete the backup.

  184.    </p><p>

  185.     <code class="function">pg_switch_wal</code> moves to the next write-ahead log file, allowing the

  186.     current file to be archived (assuming you are using continuous archiving).

  187.     The return value is the ending write-ahead log location + 1 within the just-completed write-ahead log file.

  188.     If there has been no write-ahead log activity since the last write-ahead log switch,

  189.     <code class="function">pg_switch_wal</code> does nothing and returns the start location

  190.     of the write-ahead log file currently in use.

  191.    </p><p>

  192.     <code class="function">pg_create_restore_point</code> creates a named write-ahead log

  193.     record that can be used as recovery target, and returns the corresponding

  194.     write-ahead log location.  The given name can then be used with

  195.     <a class="xref" href="runtime-config-wal.html#GUC-RECOVERY-TARGET-NAME">recovery_target_name</a> to specify the point up to which

  196.     recovery will proceed.  Avoid creating multiple restore points with the

  197.     same name, since recovery will stop at the first one whose name matches

  198.     the recovery target.

  199.    </p><p>

  200.     <code class="function">pg_current_wal_lsn</code> displays the current write-ahead log write

  201.     location in the same format used by the above functions.  Similarly,

  202.     <code class="function">pg_current_wal_insert_lsn</code> displays the current write-ahead log

  203.     insertion location and <code class="function">pg_current_wal_flush_lsn</code> displays the

  204.     current write-ahead log flush location. The insertion location is the <span class="quote">“<span class="quote">logical</span>”</span>

  205.     end of the write-ahead log at any instant, while the write location is the end of

  206.     what has actually been written out from the server's internal buffers and flush

  207.     location is the location guaranteed to be written to durable storage. The write

  208.     location is the end of what can be examined from outside the server, and is usually

  209.     what you want if you are interested in archiving partially-complete write-ahead log

  210.     files.  The insertion and flush locations are made available primarily for server

  211.     debugging purposes.  These are both read-only operations and do not

  212.     require superuser permissions.

  213.    </p><p>

  214.     You can use <code class="function">pg_walfile_name_offset</code> to extract the

  215.     corresponding write-ahead log file name and byte offset from the results of any of the

  216.     above functions.  For example:

  217. </p><pre class="programlisting">

  218. postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());

  219.         file_name         | file_offset 

  220. --------------------------+-------------

  221.  00000001000000000000000D |     4039624

  222. (1 row)

  223. </pre><p>

  224.     Similarly, <code class="function">pg_walfile_name</code> extracts just the write-ahead log file name.

  225.     When the given write-ahead log location is exactly at a write-ahead log file boundary, both

  226.     these functions return the name of the preceding write-ahead log file.

  227.     This is usually the desired behavior for managing write-ahead log archiving

  228.     behavior, since the preceding file is the last one that currently

  229.     needs to be archived.

  230.    </p><p>

  231.     <code class="function">pg_wal_lsn_diff</code> calculates the difference in bytes

  232.     between two write-ahead log locations. It can be used with

  233.     <code class="structname">pg_stat_replication</code> or some functions shown in

  234.     <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-BACKUP-TABLE" title="Table 9.84. Backup Control Functions">Table 9.84</a> to get the replication lag.

  235.    </p><p>

  236.     For details about proper usage of these functions, see

  237.     <a class="xref" href="continuous-archiving.html" title="25.3. Continuous Archiving and Point-in-Time Recovery (PITR)">Section 25.3</a>.

  238.    </p></div><div class="sect2" id="FUNCTIONS-RECOVERY-CONTROL"><div class="titlepage"><div><div><h3 class="title">9.26.4. Recovery Control Functions</h3></div></div></div><a id="id-1.5.8.31.6.2" class="indexterm"></a><a id="id-1.5.8.31.6.3" class="indexterm"></a><a id="id-1.5.8.31.6.4" class="indexterm"></a><a id="id-1.5.8.31.6.5" class="indexterm"></a><p>

  239.     The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-RECOVERY-INFO-TABLE" title="Table 9.85. Recovery Information Functions">Table 9.85</a> provide information

  240.     about the current status of the standby.

  241.     These functions may be executed both during recovery and in normal running.

  242.    </p><div class="table" id="FUNCTIONS-RECOVERY-INFO-TABLE"><p class="title"><strong>Table 9.85. Recovery Information Functions</strong></p><div class="table-contents"><table class="table" summary="Recovery Information Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>

  243.         <code class="literal"><code class="function">pg_is_in_recovery()</code></code>

  244.         </td><td><code class="type">bool</code></td><td>True if recovery is still in progress.

  245.        </td></tr><tr><td>

  246.         <code class="literal"><code class="function">pg_last_wal_receive_lsn()</code></code>

  247.         </td><td><code class="type">pg_lsn</code></td><td>Get last write-ahead log location received and synced to disk by

  248.         streaming replication. While streaming replication is in progress

  249.         this will increase monotonically. If recovery has completed this will

  250.         remain static at

  251.         the value of the last WAL record received and synced to disk during

  252.         recovery. If streaming replication is disabled, or if it has not yet

  253.         started, the function returns NULL.

  254.        </td></tr><tr><td>

  255.         <code class="literal"><code class="function">pg_last_wal_replay_lsn()</code></code>

  256.         </td><td><code class="type">pg_lsn</code></td><td>Get last write-ahead log location replayed during recovery.

  257.         If recovery is still in progress this will increase monotonically.

  258.         If recovery has completed then this value will remain static at

  259.         the value of the last WAL record applied during that recovery.

  260.         When the server has been started normally without recovery

  261.         the function returns NULL.

  262.        </td></tr><tr><td>

  263.         <code class="literal"><code class="function">pg_last_xact_replay_timestamp()</code></code>

  264.         </td><td><code class="type">timestamp with time zone</code></td><td>Get time stamp of last transaction replayed during recovery.

  265.         This is the time at which the commit or abort WAL record for that

  266.         transaction was generated on the primary.

  267.         If no transactions have been replayed during recovery, this function

  268.         returns NULL.  Otherwise, if recovery is still in progress this will

  269.         increase monotonically.  If recovery has completed then this value will

  270.         remain static at the value of the last transaction applied during that

  271.         recovery.  When the server has been started normally without recovery

  272.         the function returns NULL.

  273.        </td></tr></tbody></table></div></div><br class="table-break" /><a id="id-1.5.8.31.6.8" class="indexterm"></a><a id="id-1.5.8.31.6.9" class="indexterm"></a><a id="id-1.5.8.31.6.10" class="indexterm"></a><a id="id-1.5.8.31.6.11" class="indexterm"></a><p>

  274.     The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-RECOVERY-CONTROL-TABLE" title="Table 9.86. Recovery Control Functions">Table 9.86</a> control the progress of recovery.

  275.     These functions may be executed only during recovery.

  276.    </p><div class="table" id="FUNCTIONS-RECOVERY-CONTROL-TABLE"><p class="title"><strong>Table 9.86. Recovery Control Functions</strong></p><div class="table-contents"><table class="table" summary="Recovery Control Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>

  277.         <code class="literal"><code class="function">pg_is_wal_replay_paused()</code></code>

  278.         </td><td><code class="type">bool</code></td><td>True if recovery is paused.

  279.        </td></tr><tr><td>

  280.         <code class="literal"><code class="function">pg_promote(<em class="parameter"><code>wait</code></em> <code class="type">boolean</code> DEFAULT true, <em class="parameter"><code>wait_seconds</code></em> <code class="type">integer</code> DEFAULT 60)</code></code>

  281.         </td><td><code class="type">boolean</code></td><td>

  282.         Promotes a physical standby server.  With <em class="parameter"><code>wait</code></em>

  283.         set to <code class="literal">true</code> (the default), the function waits until

  284.         promotion is completed or <em class="parameter"><code>wait_seconds</code></em> seconds

  285.         have passed, and returns <code class="literal">true</code> if promotion is

  286.         successful and <code class="literal">false</code> otherwise.

  287.         If <em class="parameter"><code>wait</code></em> is set to <code class="literal">false</code>, the

  288.         function returns <code class="literal">true</code> immediately after sending

  289.         <code class="literal">SIGUSR1</code> to the postmaster to trigger the promotion.

  290.         This function is restricted to superusers by default, but other users

  291.         can be granted EXECUTE to run the function.

  292.        </td></tr><tr><td>

  293.         <code class="literal"><code class="function">pg_wal_replay_pause()</code></code>

  294.         </td><td><code class="type">void</code></td><td>Pauses recovery immediately (restricted to superusers by default, but other users can be granted EXECUTE to run the function).

  295.        </td></tr><tr><td>

  296.         <code class="literal"><code class="function">pg_wal_replay_resume()</code></code>

  297.         </td><td><code class="type">void</code></td><td>Restarts recovery if it was paused (restricted to superusers by default, but other users can be granted EXECUTE to run the function).

  298.        </td></tr></tbody></table></div></div><br class="table-break" /><p>

  299.     While recovery is paused no further database changes are applied.

  300.     If in hot standby, all new queries will see the same consistent snapshot

  301.     of the database, and no further query conflicts will be generated until

  302.     recovery is resumed.

  303.    </p><p>

  304.     If streaming replication is disabled, the paused state may continue

  305.     indefinitely without problem. While streaming replication is in

  306.     progress WAL records will continue to be received, which will

  307.     eventually fill available disk space, depending upon the duration of

  308.     the pause, the rate of WAL generation and available disk space.

  309.    </p></div><div class="sect2" id="FUNCTIONS-SNAPSHOT-SYNCHRONIZATION"><div class="titlepage"><div><div><h3 class="title">9.26.5. Snapshot Synchronization Functions</h3></div></div></div><a id="id-1.5.8.31.7.2" class="indexterm"></a><p>

  310.     <span class="productname">PostgreSQL</span> allows database sessions to synchronize their

  311.     snapshots. A <em class="firstterm">snapshot</em> determines which data is visible to the

  312.     transaction that is using the snapshot. Synchronized snapshots are

  313.     necessary when two or more sessions need to see identical content in the

  314.     database. If two sessions just start their transactions independently,

  315.     there is always a possibility that some third transaction commits

  316.     between the executions of the two <code class="command">START TRANSACTION</code> commands,

  317.     so that one session sees the effects of that transaction and the other

  318.     does not.

  319.    </p><p>

  320.     To solve this problem, <span class="productname">PostgreSQL</span> allows a transaction to

  321.     <em class="firstterm">export</em> the snapshot it is using.  As long as the exporting

  322.     transaction remains open, other transactions can <em class="firstterm">import</em> its

  323.     snapshot, and thereby be guaranteed that they see exactly the same view

  324.     of the database that the first transaction sees.  But note that any

  325.     database changes made by any one of these transactions remain invisible

  326.     to the other transactions, as is usual for changes made by uncommitted

  327.     transactions.  So the transactions are synchronized with respect to

  328.     pre-existing data, but act normally for changes they make themselves.

  329.    </p><p>

  330.     Snapshots are exported with the <code class="function">pg_export_snapshot</code> function,

  331.     shown in <a class="xref" href="functions-admin.html#FUNCTIONS-SNAPSHOT-SYNCHRONIZATION-TABLE" title="Table 9.87. Snapshot Synchronization Functions">Table 9.87</a>, and

  332.     imported with the <a class="xref" href="sql-set-transaction.html" title="SET TRANSACTION"><span class="refentrytitle">SET TRANSACTION</span></a> command.

  333.    </p><div class="table" id="FUNCTIONS-SNAPSHOT-SYNCHRONIZATION-TABLE"><p class="title"><strong>Table 9.87. Snapshot Synchronization Functions</strong></p><div class="table-contents"><table class="table" summary="Snapshot Synchronization Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>

  334.         <code class="literal"><code class="function">pg_export_snapshot()</code></code>

  335.        </td><td><code class="type">text</code></td><td>Save the current snapshot and return its identifier</td></tr></tbody></table></div></div><br class="table-break" /><p>

  336.     The function <code class="function">pg_export_snapshot</code> saves the current snapshot

  337.     and returns a <code class="type">text</code> string identifying the snapshot.  This string

  338.     must be passed (outside the database) to clients that want to import the

  339.     snapshot.  The snapshot is available for import only until the end of the

  340.     transaction that exported it.  A transaction can export more than one

  341.     snapshot, if needed.  Note that doing so is only useful in <code class="literal">READ

  342.     COMMITTED</code> transactions, since in <code class="literal">REPEATABLE READ</code> and

  343.     higher isolation levels, transactions use the same snapshot throughout

  344.     their lifetime.  Once a transaction has exported any snapshots, it cannot

  345.     be prepared with <a class="xref" href="sql-prepare-transaction.html" title="PREPARE TRANSACTION"><span class="refentrytitle">PREPARE TRANSACTION</span></a>.

  346.    </p><p>

  347.     See  <a class="xref" href="sql-set-transaction.html" title="SET TRANSACTION"><span class="refentrytitle">SET TRANSACTION</span></a> for details of how to use an

  348.     exported snapshot.

  349.    </p></div><div class="sect2" id="FUNCTIONS-REPLICATION"><div class="titlepage"><div><div><h3 class="title">9.26.6. Replication Functions</h3></div></div></div><p>

  350.     The functions shown

  351.     in <a class="xref" href="functions-admin.html#FUNCTIONS-REPLICATION-TABLE" title="Table 9.88. Replication SQL Functions">Table 9.88</a> are for

  352.     controlling and interacting with replication features.

  353.     See <a class="xref" href="warm-standby.html#STREAMING-REPLICATION" title="26.2.5. Streaming Replication">Section 26.2.5</a>,

  354.     <a class="xref" href="warm-standby.html#STREAMING-REPLICATION-SLOTS" title="26.2.6. Replication Slots">Section 26.2.6</a>, and

  355.     <a class="xref" href="replication-origins.html" title="Chapter 49. Replication Progress Tracking">Chapter 49</a>

  356.     for information about the underlying features.

  357.     Use of functions for replication origin is restricted to superusers.

  358.     Use of functions for replication slot is restricted to superusers

  359.     and users having <code class="literal">REPLICATION</code> privilege.

  360.    </p><p>

  361.     Many of these functions have equivalent commands in the replication

  362.     protocol; see <a class="xref" href="protocol-replication.html" title="52.4. Streaming Replication Protocol">Section 52.4</a>.

  363.    </p><p>

  364.     The functions described in

  365.     <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-BACKUP" title="9.26.3. Backup Control Functions">Section 9.26.3</a>,

  366.     <a class="xref" href="functions-admin.html#FUNCTIONS-RECOVERY-CONTROL" title="9.26.4. Recovery Control Functions">Section 9.26.4</a>, and

  367.     <a class="xref" href="functions-admin.html#FUNCTIONS-SNAPSHOT-SYNCHRONIZATION" title="9.26.5. Snapshot Synchronization Functions">Section 9.26.5</a>

  368.     are also relevant for replication.

  369.    </p><div class="table" id="FUNCTIONS-REPLICATION-TABLE"><p class="title"><strong>Table 9.88. Replication <acronym class="acronym">SQL</acronym> Functions</strong></p><div class="table-contents"><table class="table" summary="Replication SQL Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Function</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>

  370.         <a id="id-1.5.8.31.8.5.2.2.1.1.1" class="indexterm"></a>

  371.         <code class="literal"><code class="function">pg_create_physical_replication_slot(<em class="parameter"><code>slot_name</code></em> <code class="type">name</code> [<span class="optional">, <em class="parameter"><code>immediately_reserve</code></em> <code class="type">boolean</code>, <em class="parameter"><code>temporary</code></em> <code class="type">boolean</code></span>])</code></code>

  372.        </td><td>

  373.         (<em class="parameter"><code>slot_name</code></em> <code class="type">name</code>, <em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>)

  374.        </td><td>

  375.         Creates a new physical replication slot named

  376.         <em class="parameter"><code>slot_name</code></em>. The optional second parameter,

  377.         when <code class="literal">true</code>, specifies that the <acronym class="acronym">LSN</acronym> for this

  378.         replication slot be reserved immediately; otherwise

  379.         the <acronym class="acronym">LSN</acronym> is reserved on first connection from a streaming

  380.         replication client. Streaming changes from a physical slot is only

  381.         possible with the streaming-replication protocol —

  382.         see <a class="xref" href="protocol-replication.html" title="52.4. Streaming Replication Protocol">Section 52.4</a>. The optional third

  383.         parameter, <em class="parameter"><code>temporary</code></em>, when set to true, specifies that

  384.         the slot should not be permanently stored to disk and is only meant

  385.         for use by current session. Temporary slots are also

  386.         released upon any error. This function corresponds

  387.         to the replication protocol command <code class="literal">CREATE_REPLICATION_SLOT

  388.         ... PHYSICAL</code>.

  389.        </td></tr><tr><td>

  390.         <a id="id-1.5.8.31.8.5.2.2.2.1.1" class="indexterm"></a>

  391.         <code class="literal"><code class="function">pg_drop_replication_slot(<em class="parameter"><code>slot_name</code></em> <code class="type">name</code>)</code></code>

  392.        </td><td>

  393.         <code class="type">void</code>

  394.        </td><td>

  395.         Drops the physical or logical replication slot

  396.         named <em class="parameter"><code>slot_name</code></em>. Same as replication protocol

  397.         command <code class="literal">DROP_REPLICATION_SLOT</code>. For logical slots, this must

  398.         be called when connected to the same database the slot was created on.

  399.        </td></tr><tr><td>

  400.         <a id="id-1.5.8.31.8.5.2.2.3.1.1" class="indexterm"></a>

  401.         <code class="literal"><code class="function">pg_create_logical_replication_slot(<em class="parameter"><code>slot_name</code></em> <code class="type">name</code>, <em class="parameter"><code>plugin</code></em> <code class="type">name</code> [<span class="optional">, <em class="parameter"><code>temporary</code></em> <code class="type">boolean</code></span>])</code></code>

  402.        </td><td>

  403.         (<em class="parameter"><code>slot_name</code></em> <code class="type">name</code>, <em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>)

  404.        </td><td>

  405.         Creates a new logical (decoding) replication slot named

  406.         <em class="parameter"><code>slot_name</code></em> using the output plugin

  407.         <em class="parameter"><code>plugin</code></em>. The optional third

  408.         parameter, <em class="parameter"><code>temporary</code></em>, when set to true, specifies that

  409.         the slot should not be permanently stored to disk and is only meant

  410.         for use by current session. Temporary slots are also

  411.         released upon any error. A call to this function has the same

  412.         effect as the replication protocol command

  413.         <code class="literal">CREATE_REPLICATION_SLOT ... LOGICAL</code>.

  414.        </td></tr><tr><td>

  415.         <a id="id-1.5.8.31.8.5.2.2.4.1.1" class="indexterm"></a>

  416.         <code class="literal"><code class="function">pg_copy_physical_replication_slot(<em class="parameter"><code>src_slot_name</code></em> <code class="type">name</code>, <em class="parameter"><code>dst_slot_name</code></em> <code class="type">name</code> [<span class="optional">, <em class="parameter"><code>temporary</code></em> <code class="type">boolean</code></span>])</code></code>

  417.        </td><td>

  418.         (<em class="parameter"><code>slot_name</code></em> <code class="type">name</code>, <em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>)

  419.        </td><td>

  420.         Copies an existing physical replication slot named <em class="parameter"><code>src_slot_name</code></em>

  421.         to a physical replication slot named <em class="parameter"><code>dst_slot_name</code></em>.

  422.         The copied physical slot starts to reserve WAL from the same <acronym class="acronym">LSN</acronym> as the

  423.         source slot.

  424.         <em class="parameter"><code>temporary</code></em> is optional. If <em class="parameter"><code>temporary</code></em>

  425.         is omitted, the same value as the source slot is used.

  426.        </td></tr><tr><td>

  427.         <a id="id-1.5.8.31.8.5.2.2.5.1.1" class="indexterm"></a>

  428.         <code class="literal"><code class="function">pg_copy_logical_replication_slot(<em class="parameter"><code>src_slot_name</code></em> <code class="type">name</code>, <em class="parameter"><code>dst_slot_name</code></em> <code class="type">name</code> [<span class="optional">, <em class="parameter"><code>temporary</code></em> <code class="type">boolean</code> [<span class="optional">, <em class="parameter"><code>plugin</code></em> <code class="type">name</code></span>]</span>])</code></code>

  429.        </td><td>

  430.         (<em class="parameter"><code>slot_name</code></em> <code class="type">name</code>, <em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>)

  431.        </td><td>

  432.         Copies an existing logical replication slot named <em class="parameter"><code>src_slot_name</code></em>

  433.         to a logical replication slot named <em class="parameter"><code>dst_slot_name</code></em>

  434.         while changing the output plugin and persistence. The copied logical slot starts

  435.         from the same <acronym class="acronym">LSN</acronym> as the source logical slot. Both

  436.         <em class="parameter"><code>temporary</code></em> and <em class="parameter"><code>plugin</code></em> are optional.

  437.         If <em class="parameter"><code>temporary</code></em> or <em class="parameter"><code>plugin</code></em> are omitted,

  438.         the same values as the source logical slot are used.

  439.        </td></tr><tr><td>

  440.         <a id="id-1.5.8.31.8.5.2.2.6.1.1" class="indexterm"></a>

  441.         <code class="literal"><code class="function">pg_logical_slot_get_changes(<em class="parameter"><code>slot_name</code></em> <code class="type">name</code>, <em class="parameter"><code>upto_lsn</code></em> <code class="type">pg_lsn</code>, <em class="parameter"><code>upto_nchanges</code></em> <code class="type">int</code>, VARIADIC <em class="parameter"><code>options</code></em> <code class="type">text[]</code>)</code></code>

  442.        </td><td>

  443.         (<em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>, <em class="parameter"><code>xid</code></em> <code class="type">xid</code>, <em class="parameter"><code>data</code></em> <code class="type">text</code>)

  444.        </td><td>

  445.         Returns changes in the slot <em class="parameter"><code>slot_name</code></em>, starting

  446.         from the point at which since changes have been consumed last.  If

  447.         <em class="parameter"><code>upto_lsn</code></em> and <em class="parameter"><code>upto_nchanges</code></em> are NULL,

  448.         logical decoding will continue until end of WAL.  If

  449.         <em class="parameter"><code>upto_lsn</code></em> is non-NULL, decoding will include only

  450.         those transactions which commit prior to the specified LSN.  If

  451.         <em class="parameter"><code>upto_nchanges</code></em> is non-NULL, decoding will

  452.         stop when the number of rows produced by decoding exceeds

  453.         the specified value.  Note, however, that the actual number of

  454.         rows returned may be larger, since this limit is only checked after

  455.         adding the rows produced when decoding each new transaction commit.

  456.        </td></tr><tr><td>

  457.         <a id="id-1.5.8.31.8.5.2.2.7.1.1" class="indexterm"></a>

  458.         <code class="literal"><code class="function">pg_logical_slot_peek_changes(<em class="parameter"><code>slot_name</code></em> <code class="type">name</code>, <em class="parameter"><code>upto_lsn</code></em> <code class="type">pg_lsn</code>, <em class="parameter"><code>upto_nchanges</code></em> <code class="type">int</code>, VARIADIC <em class="parameter"><code>options</code></em> <code class="type">text[]</code>)</code></code>

  459.        </td><td>

  460.         (<em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>, <em class="parameter"><code>xid</code></em> <code class="type">xid</code>, <em class="parameter"><code>data</code></em> <code class="type">text</code>)

  461.        </td><td>

  462.         Behaves just like

  463.         the <code class="function">pg_logical_slot_get_changes()</code> function,

  464.         except that changes are not consumed; that is, they will be returned

  465.         again on future calls.

  466.        </td></tr><tr><td>

  467.         <a id="id-1.5.8.31.8.5.2.2.8.1.1" class="indexterm"></a>

  468.         <code class="literal"><code class="function">pg_logical_slot_get_binary_changes(<em class="parameter"><code>slot_name</code></em> <code class="type">name</code>, <em class="parameter"><code>upto_lsn</code></em> <code class="type">pg_lsn</code>, <em class="parameter"><code>upto_nchanges</code></em> <code class="type">int</code>, VARIADIC <em class="parameter"><code>options</code></em> <code class="type">text[]</code>)</code></code>

  469.        </td><td>

  470.         (<em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>, <em class="parameter"><code>xid</code></em> <code class="type">xid</code>, <em class="parameter"><code>data</code></em> <code class="type">bytea</code>)

  471.        </td><td>

  472.         Behaves just like

  473.         the <code class="function">pg_logical_slot_get_changes()</code> function,

  474.         except that changes are returned as <code class="type">bytea</code>.

  475.        </td></tr><tr><td>

  476.         <a id="id-1.5.8.31.8.5.2.2.9.1.1" class="indexterm"></a>

  477.         <code class="literal"><code class="function">pg_logical_slot_peek_binary_changes(<em class="parameter"><code>slot_name</code></em> <code class="type">name</code>, <em class="parameter"><code>upto_lsn</code></em> <code class="type">pg_lsn</code>, <em class="parameter"><code>upto_nchanges</code></em> <code class="type">int</code>, VARIADIC <em class="parameter"><code>options</code></em> <code class="type">text[]</code>)</code></code>

  478.        </td><td>

  479.         (<em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>, <em class="parameter"><code>xid</code></em> <code class="type">xid</code>, <em class="parameter"><code>data</code></em> <code class="type">bytea</code>)

  480.        </td><td>

  481.         Behaves just like

  482.         the <code class="function">pg_logical_slot_get_changes()</code> function,

  483.         except that changes are returned as <code class="type">bytea</code> and that

  484.         changes are not consumed; that is, they will be returned again

  485.         on future calls.

  486.        </td></tr><tr><td>

  487.         <a id="id-1.5.8.31.8.5.2.2.10.1.1" class="indexterm"></a>

  488.         <code class="literal"><code class="function">pg_replication_slot_advance(<em class="parameter"><code>slot_name</code></em> <code class="type">name</code>, <em class="parameter"><code>upto_lsn</code></em> <code class="type">pg_lsn</code>)</code></code>

  489.        </td><td>

  490.         (<em class="parameter"><code>slot_name</code></em> <code class="type">name</code>, <em class="parameter"><code>end_lsn</code></em> <code class="type">pg_lsn</code>)

  491.         <code class="type">bool</code>

  492.        </td><td>

  493.         Advances the current confirmed position of a replication slot named

  494.         <em class="parameter"><code>slot_name</code></em>. The slot will not be moved backwards,

  495.         and it will not be moved beyond the current insert location. Returns

  496.         the name of the slot and the real position to which it was advanced to.

  497.         The information of the updated slot is written out at the follow-up

  498.         checkpoint if any advancing is done. In the event of a crash, the

  499.         slot may return to an earlier position.

  500.        </td></tr><tr><td id="PG-REPLICATION-ORIGIN-CREATE">

  501.         <a id="id-1.5.8.31.8.5.2.2.11.1.1" class="indexterm"></a>

  502.         <code class="literal"><code class="function">pg_replication_origin_create(<em class="parameter"><code>node_name</code></em> <code class="type">text</code>)</code></code>

  503.        </td><td>

  504.         <code class="type">oid</code>

  505.        </td><td>

  506.         Create a replication origin with the given external

  507.         name, and return the internal id assigned to it.

  508.        </td></tr><tr><td id="PG-REPLICATION-ORIGIN-DROP">

  509.         <a id="id-1.5.8.31.8.5.2.2.12.1.1" class="indexterm"></a>

  510.         <code class="literal"><code class="function">pg_replication_origin_drop(<em class="parameter"><code>node_name</code></em> <code class="type">text</code>)</code></code>

  511.        </td><td>

  512.         <code class="type">void</code>

  513.        </td><td>

  514.         Delete a previously created replication origin, including any

  515.         associated replay progress.

  516.        </td></tr><tr><td>

  517.         <a id="id-1.5.8.31.8.5.2.2.13.1.1" class="indexterm"></a>

  518.         <code class="literal"><code class="function">pg_replication_origin_oid(<em class="parameter"><code>node_name</code></em> <code class="type">text</code>)</code></code>

  519.        </td><td>

  520.         <code class="type">oid</code>

  521.        </td><td>

  522.         Lookup a replication origin by name and return the internal id. If no

  523.         corresponding replication origin is found an error is thrown.

  524.        </td></tr><tr><td id="PG-REPLICATION-ORIGIN-SESSION-SETUP">

  525.         <a id="id-1.5.8.31.8.5.2.2.14.1.1" class="indexterm"></a>

  526.         <code class="literal"><code class="function">pg_replication_origin_session_setup(<em class="parameter"><code>node_name</code></em> <code class="type">text</code>)</code></code>

  527.        </td><td>

  528.         <code class="type">void</code>

  529.        </td><td>

  530.         Mark the current session as replaying from the given

  531.         origin, allowing replay progress to be tracked.  Use

  532.         <code class="function">pg_replication_origin_session_reset</code> to revert.

  533.         Can only be used if no previous origin is configured.

  534.        </td></tr><tr><td>

  535.         <a id="id-1.5.8.31.8.5.2.2.15.1.1" class="indexterm"></a>

  536.         <code class="literal"><code class="function">pg_replication_origin_session_reset()</code></code>

  537.        </td><td>

  538.         <code class="type">void</code>

  539.        </td><td>

  540.         Cancel the effects

  541.         of <code class="function">pg_replication_origin_session_setup()</code>.

  542.        </td></tr><tr><td>

  543.         <a id="id-1.5.8.31.8.5.2.2.16.1.1" class="indexterm"></a>

  544.         <code class="literal"><code class="function">pg_replication_origin_session_is_setup()</code></code>

  545.        </td><td>

  546.         <code class="type">bool</code>

  547.        </td><td>

  548.         Has a replication origin been configured in the current session?

  549.        </td></tr><tr><td id="PG-REPLICATION-ORIGIN-SESSION-PROGRESS">

  550.         <a id="id-1.5.8.31.8.5.2.2.17.1.1" class="indexterm"></a>

  551.         <code class="literal"><code class="function">pg_replication_origin_session_progress(<em class="parameter"><code>flush</code></em> <code class="type">bool</code>)</code></code>

  552.        </td><td>

  553.         <code class="type">pg_lsn</code>

  554.        </td><td>

  555.         Return the replay location for the replication origin configured in

  556.         the current session. The parameter <em class="parameter"><code>flush</code></em>

  557.         determines whether the corresponding local transaction will be

  558.         guaranteed to have been flushed to disk or not.

  559.        </td></tr><tr><td id="PG-REPLICATION-ORIGIN-XACT-SETUP">

  560.         <a id="id-1.5.8.31.8.5.2.2.18.1.1" class="indexterm"></a>

  561.         <code class="literal"><code class="function">pg_replication_origin_xact_setup(<em class="parameter"><code>origin_lsn</code></em> <code class="type">pg_lsn</code>, <em class="parameter"><code>origin_timestamp</code></em> <code class="type">timestamptz</code>)</code></code>

  562.        </td><td>

  563.         <code class="type">void</code>

  564.        </td><td>

  565.         Mark the current transaction as replaying a transaction that has

  566.         committed at the given <acronym class="acronym">LSN</acronym> and timestamp. Can

  567.         only be called when a replication origin has previously been

  568.         configured using

  569.         <code class="function">pg_replication_origin_session_setup()</code>.

  570.        </td></tr><tr><td id="PG-REPLICATION-ORIGIN-XACT-RESET">

  571.         <a id="id-1.5.8.31.8.5.2.2.19.1.1" class="indexterm"></a>

  572.         <code class="literal"><code class="function">pg_replication_origin_xact_reset()</code></code>

  573.        </td><td>

  574.         <code class="type">void</code>

  575.        </td><td>

  576.         Cancel the effects of

  577.         <code class="function">pg_replication_origin_xact_setup()</code>.

  578.        </td></tr><tr><td id="PG-REPLICATION-ORIGIN-ADVANCE">

  579.         <a id="id-1.5.8.31.8.5.2.2.20.1.1" class="indexterm"></a>

  580.         <code class="literal">pg_replication_origin_advance<code class="function">(<em class="parameter"><code>node_name</code></em> <code class="type">text</code>, <em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>)</code></code>

  581.        </td><td>

  582.         <code class="type">void</code>

  583.        </td><td>

  584.         Set replication progress for the given node to the given

  585.         location. This primarily is useful for setting up the initial location

  586.         or a new location after configuration changes and similar. Be aware

  587.         that careless use of this function can lead to inconsistently

  588.         replicated data.

  589.        </td></tr><tr><td id="PG-REPLICATION-ORIGIN-PROGRESS">

  590.         <a id="id-1.5.8.31.8.5.2.2.21.1.1" class="indexterm"></a>

  591.         <code class="literal"><code class="function">pg_replication_origin_progress(<em class="parameter"><code>node_name</code></em> <code class="type">text</code>, <em class="parameter"><code>flush</code></em> <code class="type">bool</code>)</code></code>

  592.        </td><td>

  593.         <code class="type">pg_lsn</code>

  594.        </td><td>

  595.         Return the replay location for the given replication origin. The

  596.         parameter <em class="parameter"><code>flush</code></em> determines whether the

  597.         corresponding local transaction will be guaranteed to have been

  598.         flushed to disk or not.

  599.        </td></tr><tr><td id="PG-LOGICAL-EMIT-MESSAGE-TEXT">

  600.         <a id="id-1.5.8.31.8.5.2.2.22.1.1" class="indexterm"></a>

  601.         <code class="literal"><code class="function">pg_logical_emit_message(<em class="parameter"><code>transactional</code></em> <code class="type">bool</code>, <em class="parameter"><code>prefix</code></em> <code class="type">text</code>, <em class="parameter"><code>content</code></em> <code class="type">text</code>)</code></code>

  602.        </td><td>

  603.         <code class="type">pg_lsn</code>

  604.        </td><td>

  605.         Emit text logical decoding message. This can be used to pass generic

  606.         messages to logical decoding plugins through WAL. The parameter

  607.         <em class="parameter"><code>transactional</code></em> specifies if the message should

  608.         be part of current transaction or if it should be written immediately

  609.         and decoded as soon as the logical decoding reads the record. The

  610.         <em class="parameter"><code>prefix</code></em> is textual prefix used by the logical

  611.         decoding plugins to easily recognize interesting messages for them.

  612.         The <em class="parameter"><code>content</code></em> is the text of the message.

  613.        </td></tr><tr><td id="PG-LOGICAL-EMIT-MESSAGE-BYTEA">

  614.         <code class="literal"><code class="function">pg_logical_emit_message(<em class="parameter"><code>transactional</code></em> <code class="type">bool</code>, <em class="parameter"><code>prefix</code></em> <code class="type">text</code>, <em class="parameter"><code>content</code></em> <code class="type">bytea</code>)</code></code>

  615.        </td><td>

  616.         <code class="type">pg_lsn</code>

  617.        </td><td>

  618.         Emit binary logical decoding message. This can be used to pass generic

  619.         messages to logical decoding plugins through WAL. The parameter

  620.         <em class="parameter"><code>transactional</code></em> specifies if the message should

  621.         be part of current transaction or if it should be written immediately

  622.         and decoded as soon as the logical decoding reads the record. The

  623.         <em class="parameter"><code>prefix</code></em> is textual prefix used by the logical

  624.         decoding plugins to easily recognize interesting messages for them.

  625.         The <em class="parameter"><code>content</code></em> is the binary content of the

  626.         message.

  627.        </td></tr></tbody></table></div></div><br class="table-break" /></div><div class="sect2" id="FUNCTIONS-ADMIN-DBOBJECT"><div class="titlepage"><div><div><h3 class="title">9.26.7. Database Object Management Functions</h3></div></div></div><p>

  628.     The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-DBSIZE" title="Table 9.89. Database Object Size Functions">Table 9.89</a> calculate

  629.     the disk space usage of database objects.

  630.    </p><a id="id-1.5.8.31.9.3" class="indexterm"></a><a id="id-1.5.8.31.9.4" class="indexterm"></a><a id="id-1.5.8.31.9.5" class="indexterm"></a><a id="id-1.5.8.31.9.6" class="indexterm"></a><a id="id-1.5.8.31.9.7" class="indexterm"></a><a id="id-1.5.8.31.9.8" class="indexterm"></a><a id="id-1.5.8.31.9.9" class="indexterm"></a><a id="id-1.5.8.31.9.10" class="indexterm"></a><a id="id-1.5.8.31.9.11" class="indexterm"></a><div class="table" id="FUNCTIONS-ADMIN-DBSIZE"><p class="title"><strong>Table 9.89. Database Object Size Functions</strong></p><div class="table-contents"><table class="table" summary="Database Object Size Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td><code class="literal"><code class="function">pg_column_size(<code class="type">any</code>)</code></code></td><td><code class="type">int</code></td><td>Number of bytes used to store a particular value (possibly compressed)</td></tr><tr><td>

  631.         <code class="literal"><code class="function">pg_database_size(<code class="type">oid</code>)</code></code>

  632.         </td><td><code class="type">bigint</code></td><td>Disk space used by the database with the specified OID</td></tr><tr><td>

  633.         <code class="literal"><code class="function">pg_database_size(<code class="type">name</code>)</code></code>

  634.         </td><td><code class="type">bigint</code></td><td>Disk space used by the database with the specified name</td></tr><tr><td>

  635.         <code class="literal"><code class="function">pg_indexes_size(<code class="type">regclass</code>)</code></code>

  636.         </td><td><code class="type">bigint</code></td><td>

  637.         Total disk space used by indexes attached to the specified table

  638.        </td></tr><tr><td>

  639.         <code class="literal"><code class="function">pg_relation_size(<em class="parameter"><code>relation</code></em> <code class="type">regclass</code>, <em class="parameter"><code>fork</code></em> <code class="type">text</code>)</code></code>

  640.         </td><td><code class="type">bigint</code></td><td>

  641.         Disk space used by the specified fork (<code class="literal">'main'</code>,

  642.         <code class="literal">'fsm'</code>, <code class="literal">'vm'</code>, or <code class="literal">'init'</code>)

  643.         of the specified table or index

  644.        </td></tr><tr><td>

  645.         <code class="literal"><code class="function">pg_relation_size(<em class="parameter"><code>relation</code></em> <code class="type">regclass</code>)</code></code>

  646.         </td><td><code class="type">bigint</code></td><td>

  647.         Shorthand for <code class="literal">pg_relation_size(..., 'main')</code>

  648.        </td></tr><tr><td>

  649.         <code class="literal"><code class="function">pg_size_bytes(<code class="type">text</code>)</code></code>

  650.         </td><td><code class="type">bigint</code></td><td>

  651.          Converts a size in human-readable format with size units into bytes

  652.        </td></tr><tr><td>

  653.         <code class="literal"><code class="function">pg_size_pretty(<code class="type">bigint</code>)</code></code>

  654.         </td><td><code class="type">text</code></td><td>

  655.          Converts a size in bytes expressed as a 64-bit integer into a

  656.          human-readable format with size units

  657.        </td></tr><tr><td>

  658.         <code class="literal"><code class="function">pg_size_pretty(<code class="type">numeric</code>)</code></code>

  659.         </td><td><code class="type">text</code></td><td>

  660.          Converts a size in bytes expressed as a numeric value into a

  661.          human-readable format with size units

  662.        </td></tr><tr><td>

  663.         <code class="literal"><code class="function">pg_table_size(<code class="type">regclass</code>)</code></code>

  664.         </td><td><code class="type">bigint</code></td><td>

  665.         Disk space used by the specified table, excluding indexes

  666.         (but including TOAST, free space map, and visibility map)

  667.        </td></tr><tr><td>

  668.         <code class="literal"><code class="function">pg_tablespace_size(<code class="type">oid</code>)</code></code>

  669.         </td><td><code class="type">bigint</code></td><td>Disk space used by the tablespace with the specified OID</td></tr><tr><td>

  670.         <code class="literal"><code class="function">pg_tablespace_size(<code class="type">name</code>)</code></code>

  671.         </td><td><code class="type">bigint</code></td><td>Disk space used by the tablespace with the specified name</td></tr><tr><td>

  672.         <code class="literal"><code class="function">pg_total_relation_size(<code class="type">regclass</code>)</code></code>

  673.         </td><td><code class="type">bigint</code></td><td>

  674.         Total disk space used by the specified table,

  675.         including all indexes and <acronym class="acronym">TOAST</acronym> data

  676.        </td></tr></tbody></table></div></div><br class="table-break" /><p>

  677.     <code class="function">pg_column_size</code> shows the space used to store any individual

  678.     data value.

  679.    </p><p>

  680.     <code class="function">pg_total_relation_size</code> accepts the OID or name of a

  681.     table or toast table, and returns the total on-disk space used for

  682.     that table, including all associated indexes.  This function is

  683.     equivalent to <code class="function">pg_table_size</code>

  684.     <code class="literal">+</code> <code class="function">pg_indexes_size</code>.

  685.    </p><p>

  686.     <code class="function">pg_table_size</code> accepts the OID or name of a table and

  687.     returns the disk space needed for that table, exclusive of indexes.

  688.     (TOAST space, free space map, and visibility map are included.)

  689.    </p><p>

  690.     <code class="function">pg_indexes_size</code> accepts the OID or name of a table and

  691.     returns the total disk space used by all the indexes attached to that

  692.     table.

  693.    </p><p>

  694.     <code class="function">pg_database_size</code> and <code class="function">pg_tablespace_size</code>

  695.     accept the OID or name of a database or tablespace, and return the total

  696.     disk space used therein.  To use <code class="function">pg_database_size</code>,

  697.     you must have <code class="literal">CONNECT</code> permission on the specified database

  698.     (which is granted by default), or be a member of the <code class="literal">pg_read_all_stats</code>

  699.     role. To use <code class="function">pg_tablespace_size</code>, you must have

  700.     <code class="literal">CREATE</code> permission on the specified tablespace, or be a member

  701.     of the <code class="literal">pg_read_all_stats</code> role unless it is the default tablespace for

  702.     the current database.

  703.    </p><p>

  704.     <code class="function">pg_relation_size</code> accepts the OID or name of a table, index

  705.     or toast table, and returns the on-disk size in bytes of one fork of

  706.     that relation.  (Note that for most purposes it is more convenient to

  707.     use the higher-level functions <code class="function">pg_total_relation_size</code>

  708.     or <code class="function">pg_table_size</code>, which sum the sizes of all forks.)

  709.     With one argument, it returns the size of the main data fork of the

  710.     relation.  The second argument can be provided to specify which fork

  711.     to examine:

  712.     </p><div class="itemizedlist"><ul class="itemizedlist compact" style="list-style-type: disc; "><li class="listitem"><p>

  713.        <code class="literal">'main'</code> returns the size of the main

  714.        data fork of the relation.

  715.       </p></li><li class="listitem"><p>

  716.        <code class="literal">'fsm'</code> returns the size of the Free Space Map

  717.        (see <a class="xref" href="storage-fsm.html" title="68.3. Free Space Map">Section 68.3</a>) associated with the relation.

  718.       </p></li><li class="listitem"><p>

  719.        <code class="literal">'vm'</code> returns the size of the Visibility Map

  720.        (see <a class="xref" href="storage-vm.html" title="68.4. Visibility Map">Section 68.4</a>) associated with the relation.

  721.       </p></li><li class="listitem"><p>

  722.        <code class="literal">'init'</code> returns the size of the initialization

  723.        fork, if any, associated with the relation.

  724.       </p></li></ul></div><p>

  725.    </p><p>

  726.     <code class="function">pg_size_pretty</code> can be used to format the result of one of

  727.     the other functions in a human-readable way, using bytes, kB, MB, GB or TB

  728.     as appropriate.

  729.    </p><p>

  730.     <code class="function">pg_size_bytes</code> can be used to get the size in bytes from a

  731.     string in human-readable format. The input may have units of bytes, kB,

  732.     MB, GB or TB, and is parsed case-insensitively. If no units are specified,

  733.     bytes are assumed.

  734.    </p><div class="note"><h3 class="title">Note</h3><p>

  735.      The units kB, MB, GB and TB used by the functions

  736.      <code class="function">pg_size_pretty</code> and <code class="function">pg_size_bytes</code> are defined

  737.      using powers of 2 rather than powers of 10, so 1kB is 1024 bytes, 1MB is

  738.      1024<sup>2</sup> = 1048576 bytes, and so on.

  739.     </p></div><p>

  740.     The functions above that operate on tables or indexes accept a

  741.     <code class="type">regclass</code> argument, which is simply the OID of the table or index

  742.     in the <code class="structname">pg_class</code> system catalog.  You do not have to look up

  743.     the OID by hand, however, since the <code class="type">regclass</code> data type's input

  744.     converter will do the work for you.  Just write the table name enclosed in

  745.     single quotes so that it looks like a literal constant.  For compatibility

  746.     with the handling of ordinary <acronym class="acronym">SQL</acronym> names, the string

  747.     will be converted to lower case unless it contains double quotes around

  748.     the table name.

  749.    </p><p>

  750.     If an OID that does not represent an existing object is passed as

  751.     argument to one of the above functions, NULL is returned.

  752.    </p><p>

  753.     The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-DBLOCATION" title="Table 9.90. Database Object Location Functions">Table 9.90</a> assist

  754.     in identifying the specific disk files associated with database objects.

  755.    </p><a id="id-1.5.8.31.9.25" class="indexterm"></a><a id="id-1.5.8.31.9.26" class="indexterm"></a><a id="id-1.5.8.31.9.27" class="indexterm"></a><div class="table" id="FUNCTIONS-ADMIN-DBLOCATION"><p class="title"><strong>Table 9.90. Database Object Location Functions</strong></p><div class="table-contents"><table class="table" summary="Database Object Location Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>

  756.         <code class="literal"><code class="function">pg_relation_filenode(<em class="parameter"><code>relation</code></em> <code class="type">regclass</code>)</code></code>

  757.         </td><td><code class="type">oid</code></td><td>

  758.         Filenode number of the specified relation

  759.        </td></tr><tr><td>

  760.         <code class="literal"><code class="function">pg_relation_filepath(<em class="parameter"><code>relation</code></em> <code class="type">regclass</code>)</code></code>

  761.         </td><td><code class="type">text</code></td><td>

  762.         File path name of the specified relation

  763.        </td></tr><tr><td>

  764.         <code class="literal"><code class="function">pg_filenode_relation(<em class="parameter"><code>tablespace</code></em> <code class="type">oid</code>, <em class="parameter"><code>filenode</code></em> <code class="type">oid</code>)</code></code>

  765.         </td><td><code class="type">regclass</code></td><td>

  766.         Find the relation associated with a given tablespace and filenode

  767.        </td></tr></tbody></table></div></div><br class="table-break" /><p>

  768.     <code class="function">pg_relation_filenode</code> accepts the OID or name of a table,

  769.     index, sequence, or toast table, and returns the <span class="quote">“<span class="quote">filenode</span>”</span> number

  770.     currently assigned to it.  The filenode is the base component of the file

  771.     name(s) used for the relation (see <a class="xref" href="storage-file-layout.html" title="68.1. Database File Layout">Section 68.1</a>

  772.     for more information).  For most tables the result is the same as

  773.     <code class="structname">pg_class</code>.<code class="structfield">relfilenode</code>, but for certain

  774.     system catalogs <code class="structfield">relfilenode</code> is zero and this function must

  775.     be used to get the correct value.  The function returns NULL if passed

  776.     a relation that does not have storage, such as a view.

  777.    </p><p>

  778.     <code class="function">pg_relation_filepath</code> is similar to

  779.     <code class="function">pg_relation_filenode</code>, but it returns the entire file path name

  780.     (relative to the database cluster's data directory <code class="varname">PGDATA</code>) of

  781.     the relation.

  782.    </p><p>

  783.     <code class="function">pg_filenode_relation</code> is the reverse of

  784.     <code class="function">pg_relation_filenode</code>. Given a <span class="quote">“<span class="quote">tablespace</span>”</span> OID and

  785.     a <span class="quote">“<span class="quote">filenode</span>”</span>, it returns the associated relation's OID. For a table

  786.     in the database's default tablespace, the tablespace can be specified as 0.

  787.    </p><p>

  788.     <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-COLLATION" title="Table 9.91. Collation Management Functions">Table 9.91</a> lists functions used to manage

  789.     collations.

  790.    </p><div class="table" id="FUNCTIONS-ADMIN-COLLATION"><p class="title"><strong>Table 9.91. Collation Management Functions</strong></p><div class="table-contents"><table class="table" summary="Collation Management Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>

  791.         <a id="id-1.5.8.31.9.33.2.2.1.1.1" class="indexterm"></a>

  792.         <code class="literal"><code class="function">pg_collation_actual_version(<code class="type">oid</code>)</code></code>

  793.        </td><td><code class="type">text</code></td><td>Return actual version of collation from operating system</td></tr><tr><td>

  794.         <a id="id-1.5.8.31.9.33.2.2.2.1.1" class="indexterm"></a>

  795.         <code class="literal"><code class="function">pg_import_system_collations(<em class="parameter"><code>schema</code></em> <code class="type">regnamespace</code>)</code></code>

  796.        </td><td><code class="type">integer</code></td><td>Import operating system collations</td></tr></tbody></table></div></div><br class="table-break" /><p>

  797.     <code class="function">pg_collation_actual_version</code> returns the actual

  798.     version of the collation object as it is currently installed in the

  799.     operating system.  If this is different from the value

  800.     in <code class="literal">pg_collation.collversion</code>, then objects depending on

  801.     the collation might need to be rebuilt.  See also

  802.     <a class="xref" href="sql-altercollation.html" title="ALTER COLLATION"><span class="refentrytitle">ALTER COLLATION</span></a>.

  803.    </p><p>

  804.     <code class="function">pg_import_system_collations</code> adds collations to the system

  805.     catalog <code class="literal">pg_collation</code> based on all the

  806.     locales it finds in the operating system.  This is

  807.     what <code class="command">initdb</code> uses;

  808.     see <a class="xref" href="collation.html#COLLATION-MANAGING" title="23.2.2. Managing Collations">Section 23.2.2</a> for more details.  If additional

  809.     locales are installed into the operating system later on, this function

  810.     can be run again to add collations for the new locales.  Locales that

  811.     match existing entries in <code class="literal">pg_collation</code> will be skipped.

  812.     (But collation objects based on locales that are no longer

  813.     present in the operating system are not removed by this function.)

  814.     The <em class="parameter"><code>schema</code></em> parameter would typically

  815.     be <code class="literal">pg_catalog</code>, but that is not a requirement;

  816.     the collations could be installed into some other schema as well.

  817.     The function returns the number of new collation objects it created.

  818.    </p><div class="table" id="FUNCTIONS-INFO-PARTITION"><p class="title"><strong>Table 9.92. Partitioning Information Functions</strong></p><div class="table-contents"><table class="table" summary="Partitioning Information Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>

  819.         <a id="id-1.5.8.31.9.36.2.2.1.1.1" class="indexterm"></a>

  820.         <code class="literal"><code class="function">pg_partition_tree(<code class="type">regclass</code>)</code></code>

  821.        </td><td><code class="type">setof record</code></td><td>

  822.         List information about tables or indexes in a partition tree for a

  823.         given partitioned table or partitioned index, with one row for each

  824.         partition.  Information provided includes the name of the partition,

  825.         the name of its immediate parent, a boolean value telling if the

  826.         partition is a leaf, and an integer telling its level in the hierarchy.

  827.         The value of level begins at <code class="literal">0</code> for the input table

  828.         or index in its role as the root of the partition tree,

  829.         <code class="literal">1</code> for its partitions, <code class="literal">2</code> for

  830.         their partitions, and so on.

  831.        </td></tr><tr><td>

  832.         <a id="id-1.5.8.31.9.36.2.2.2.1.1" class="indexterm"></a>

  833.         <code class="literal"><code class="function">pg_partition_ancestors(<code class="type">regclass</code>)</code></code>

  834.        </td><td><code class="type">setof regclass</code></td><td>

  835.         List the ancestor relations of the given partition,

  836.         including the partition itself.

  837.        </td></tr><tr><td>

  838.         <a id="id-1.5.8.31.9.36.2.2.3.1.1" class="indexterm"></a>

  839.         <code class="literal"><code class="function">pg_partition_root(<code class="type">regclass</code>)</code></code>

  840.        </td><td><code class="type">regclass</code></td><td>

  841.         Return the top-most parent of a partition tree to which the given

  842.         relation belongs.

  843.        </td></tr></tbody></table></div></div><br class="table-break" /><p>

  844.     To check the total size of the data contained in

  845.     <code class="structname">measurement</code> table described in

  846.     <a class="xref" href="ddl-partitioning.html#DDL-PARTITIONING-DECLARATIVE-EXAMPLE" title="5.11.2.1. Example">Section 5.11.2.1</a>, one could use the

  847.     following query:

  848.    </p><pre class="programlisting">

  849. =# SELECT pg_size_pretty(sum(pg_relation_size(relid))) AS total_size

  850.      FROM pg_partition_tree('measurement');

  851.  total_size 

  852. ------------

  853.  24 kB

  854. (1 row)

  855. </pre></div><div class="sect2" id="FUNCTIONS-ADMIN-INDEX"><div class="titlepage"><div><div><h3 class="title">9.26.8. Index Maintenance Functions</h3></div></div></div><a id="id-1.5.8.31.10.2" class="indexterm"></a><a id="id-1.5.8.31.10.3" class="indexterm"></a><a id="id-1.5.8.31.10.4" class="indexterm"></a><a id="id-1.5.8.31.10.5" class="indexterm"></a><p>

  856.     <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-INDEX-TABLE" title="Table 9.93. Index Maintenance Functions">Table 9.93</a> shows the functions

  857.     available for index maintenance tasks.

  858.     These functions cannot be executed during recovery.

  859.     Use of these functions is restricted to superusers and the owner

  860.     of the given index.

  861.    </p><div class="table" id="FUNCTIONS-ADMIN-INDEX-TABLE"><p class="title"><strong>Table 9.93. Index Maintenance Functions</strong></p><div class="table-contents"><table class="table" summary="Index Maintenance Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>

  862.         <code class="literal"><code class="function">brin_summarize_new_values(<em class="parameter"><code>index</code></em> <code class="type">regclass</code>)</code></code>

  863.        </td><td><code class="type">integer</code></td><td>summarize page ranges not already summarized</td></tr><tr><td>

  864.         <code class="literal"><code class="function">brin_summarize_range(<em class="parameter"><code>index</code></em> <code class="type">regclass</code>, <em class="parameter"><code>blockNumber</code></em> <code class="type">bigint</code>)</code></code>

  865.        </td><td><code class="type">integer</code></td><td>summarize the page range covering the given block, if not already summarized</td></tr><tr><td>

  866.         <code class="literal"><code class="function">brin_desummarize_range(<em class="parameter"><code>index</code></em> <code class="type">regclass</code>, <em class="parameter"><code>blockNumber</code></em> <code class="type">bigint</code>)</code></code>

  867.        </td><td><code class="type">integer</code></td><td>de-summarize the page range covering the given block, if summarized</td></tr><tr><td>

  868.         <code class="literal"><code class="function">gin_clean_pending_list(<em class="parameter"><code>index</code></em> <code class="type">regclass</code>)</code></code>

  869.        </td><td><code class="type">bigint</code></td><td>move GIN pending list entries into main index structure</td></tr></tbody></table></div></div><br class="table-break" /><p>

  870.     <code class="function">brin_summarize_new_values</code> accepts the OID or name of a

  871.     BRIN index and inspects the index to find page ranges in the base table

  872.     that are not currently summarized by the index; for any such range

  873.     it creates a new summary index tuple by scanning the table pages.

  874.     It returns the number of new page range summaries that were inserted

  875.     into the index.  <code class="function">brin_summarize_range</code> does the same, except

  876.     it only summarizes the range that covers the given block number.

  877.    </p><p>

  878.     <code class="function">gin_clean_pending_list</code> accepts the OID or name of

  879.     a GIN index and cleans up the pending list of the specified index

  880.     by moving entries in it to the main GIN data structure in bulk.

  881.     It returns the number of pages removed from the pending list.

  882.     Note that if the argument is a GIN index built with

  883.     the <code class="literal">fastupdate</code> option disabled, no cleanup happens and the

  884.     return value is 0, because the index doesn't have a pending list.

  885.     Please see <a class="xref" href="gin-implementation.html#GIN-FAST-UPDATE" title="66.4.1. GIN Fast Update Technique">Section 66.4.1</a> and <a class="xref" href="gin-tips.html" title="66.5. GIN Tips and Tricks">Section 66.5</a>

  886.     for details of the pending list and <code class="literal">fastupdate</code> option.

  887.    </p></div><div class="sect2" id="FUNCTIONS-ADMIN-GENFILE"><div class="titlepage"><div><div><h3 class="title">9.26.9. Generic File Access Functions</h3></div></div></div><p>

  888.     The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-GENFILE-TABLE" title="Table 9.94. Generic File Access Functions">Table 9.94</a> provide native access to

  889.     files on the machine hosting the server. Only files within the

  890.     database cluster directory and the <code class="varname">log_directory</code> can be

  891.     accessed unless the user is granted the role

  892.     <code class="literal">pg_read_server_files</code>.  Use a relative path for files in

  893.     the cluster directory, and a path matching the <code class="varname">log_directory</code>

  894.     configuration setting for log files.

  895.    </p><p>

  896.     Note that granting users the EXECUTE privilege on

  897.     <code class="function">pg_read_file()</code>, or related functions, allows them the

  898.     ability to read any file on the server which the database can read and

  899.     that those reads bypass all in-database privilege checks.  This means that,

  900.     among other things, a user with this access is able to read the contents of the

  901.     <code class="literal">pg_authid</code> table where authentication information is contained,

  902.     as well as read any file in the database.  Therefore, granting access to these

  903.     functions should be carefully considered.

  904.    </p><div class="table" id="FUNCTIONS-ADMIN-GENFILE-TABLE"><p class="title"><strong>Table 9.94. Generic File Access Functions</strong></p><div class="table-contents"><table class="table" summary="Generic File Access Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>

  905.         <code class="literal"><code class="function">pg_ls_dir(<em class="parameter"><code>dirname</code></em> <code class="type">text</code> [, <em class="parameter"><code>missing_ok</code></em> <code class="type">boolean</code>, <em class="parameter"><code>include_dot_dirs</code></em> <code class="type">boolean</code>])</code></code>

  906.        </td><td><code class="type">setof text</code></td><td>

  907.         List the contents of a directory.  Restricted to superusers by default, but other users can be granted EXECUTE to run the function.

  908.        </td></tr><tr><td>

  909.         <code class="literal"><code class="function">pg_ls_logdir()</code></code>

  910.        </td><td><code class="type">setof record</code></td><td>

  911.         List the name, size, and last modification time of files in the log

  912.         directory. Access is granted to members of the <code class="literal">pg_monitor</code>

  913.         role and may be granted to other non-superuser roles.

  914.        </td></tr><tr><td>

  915.         <code class="literal"><code class="function">pg_ls_waldir()</code></code>

  916.        </td><td><code class="type">setof record</code></td><td>

  917.         List the name, size, and last modification time of files in the WAL

  918.         directory. Access is granted to members of the <code class="literal">pg_monitor</code>

  919.         role and may be granted to other non-superuser roles.

  920.        </td></tr><tr><td>

  921.         <code class="literal"><code class="function">pg_ls_archive_statusdir()</code></code>

  922.        </td><td><code class="type">setof record</code></td><td>

  923.         List the name, size, and last modification time of files in the WAL

  924.         archive status directory. Access is granted to members of the

  925.         <code class="literal">pg_monitor</code> role and may be granted to other

  926.         non-superuser roles.

  927.        </td></tr><tr><td>

  928.         <code class="literal"><code class="function">pg_ls_tmpdir([<span class="optional"><em class="parameter"><code>tablespace</code></em> <code class="type">oid</code></span>])</code></code>

  929.        </td><td><code class="type">setof record</code></td><td>

  930.         List the name, size, and last modification time of files in the

  931.         temporary directory for <em class="parameter"><code>tablespace</code></em>.  If

  932.         <em class="parameter"><code>tablespace</code></em> is not provided, the

  933.         <code class="literal">pg_default</code> tablespace is used.  Access is granted

  934.         to members of the <code class="literal">pg_monitor</code> role and may be

  935.         granted to other non-superuser roles.

  936.        </td></tr><tr><td>

  937.         <code class="literal"><code class="function">pg_read_file(<em class="parameter"><code>filename</code></em> <code class="type">text</code> [, <em class="parameter"><code>offset</code></em> <code class="type">bigint</code>, <em class="parameter"><code>length</code></em> <code class="type">bigint</code> [, <em class="parameter"><code>missing_ok</code></em> <code class="type">boolean</code>] ])</code></code>

  938.        </td><td><code class="type">text</code></td><td>

  939.         Return the contents of a text file.  Restricted to superusers by default, but other users can be granted EXECUTE to run the function.

  940.        </td></tr><tr><td>

  941.         <code class="literal"><code class="function">pg_read_binary_file(<em class="parameter"><code>filename</code></em> <code class="type">text</code> [, <em class="parameter"><code>offset</code></em> <code class="type">bigint</code>, <em class="parameter"><code>length</code></em> <code class="type">bigint</code> [, <em class="parameter"><code>missing_ok</code></em> <code class="type">boolean</code>] ])</code></code>

  942.        </td><td><code class="type">bytea</code></td><td>

  943.         Return the contents of a file.  Restricted to superusers by default, but other users can be granted EXECUTE to run the function.

  944.        </td></tr><tr><td>

  945.         <code class="literal"><code class="function">pg_stat_file(<em class="parameter"><code>filename</code></em> <code class="type">text</code>[, <em class="parameter"><code>missing_ok</code></em> <code class="type">boolean</code>])</code></code>

  946.        </td><td><code class="type">record</code></td><td>

  947.         Return information about a file.  Restricted to superusers by default, but other users can be granted EXECUTE to run the function.

  948.        </td></tr></tbody></table></div></div><br class="table-break" /><p>

  949.     Some of these functions take an optional <em class="parameter"><code>missing_ok</code></em> parameter,

  950.     which specifies the behavior when the file or directory does not exist.

  951.     If <code class="literal">true</code>, the function returns NULL (except

  952.     <code class="function">pg_ls_dir</code>, which returns an empty result set). If

  953.     <code class="literal">false</code>, an error is raised. The default is <code class="literal">false</code>.

  954.    </p><a id="id-1.5.8.31.11.6" class="indexterm"></a><p>

  955.     <code class="function">pg_ls_dir</code> returns the names of all files (and directories

  956.     and other special files) in the specified directory. The <em class="parameter"><code>

  957.     include_dot_dirs</code></em> indicates whether <span class="quote">“<span class="quote">.</span>”</span> and <span class="quote">“<span class="quote">..</span>”</span> are

  958.     included in the result set. The default is to exclude them

  959.     (<code class="literal">false</code>), but including them can be useful when

  960.     <em class="parameter"><code>missing_ok</code></em> is <code class="literal">true</code>, to distinguish an

  961.     empty directory from an non-existent directory.

  962.    </p><a id="id-1.5.8.31.11.8" class="indexterm"></a><p>

  963.     <code class="function">pg_ls_logdir</code> returns the name, size, and last modified time

  964.     (mtime) of each file in the log directory. By default, only superusers

  965.     and members of the <code class="literal">pg_monitor</code> role can use this function.

  966.     Access may be granted to others using <code class="command">GRANT</code>.

  967.     Filenames beginning with a dot, directories, and other special files are not shown.

  968.    </p><a id="id-1.5.8.31.11.10" class="indexterm"></a><p>

  969.     <code class="function">pg_ls_waldir</code> returns the name, size, and last modified time

  970.     (mtime) of each file in the write ahead log (WAL) directory. By

  971.     default only superusers and members of the <code class="literal">pg_monitor</code> role

  972.     can use this function. Access may be granted to others using

  973.     <code class="command">GRANT</code>.

  974.     Filenames beginning with a dot, directories, and other special files are not shown.

  975.    </p><a id="id-1.5.8.31.11.12" class="indexterm"></a><p>

  976.     <code class="function">pg_ls_archive_statusdir</code> returns the name, size, and

  977.     last modified time (mtime) of each file in the WAL archive status

  978.     directory <code class="filename">pg_wal/archive_status</code>. By default only

  979.     superusers and members of the <code class="literal">pg_monitor</code> role can

  980.     use this function. Access may be granted to others using

  981.     <code class="command">GRANT</code>.

  982.     Filenames beginning with a dot, directories, and other special files are not shown.

  983.    </p><a id="id-1.5.8.31.11.14" class="indexterm"></a><p>

  984.     <code class="function">pg_ls_tmpdir</code> returns the name, size, and last modified

  985.     time (mtime) of each file in the temporary file directory for the specified

  986.     <em class="parameter"><code>tablespace</code></em>.  If <em class="parameter"><code>tablespace</code></em> is

  987.     not provided, the <code class="literal">pg_default</code> tablespace is used.  By

  988.     default only superusers and members of the <code class="literal">pg_monitor</code>

  989.     role can use this function.  Access may be granted to others using

  990.     <code class="command">GRANT</code>.

  991.     Filenames beginning with a dot, directories, and other special files are not shown.

  992.    </p><a id="id-1.5.8.31.11.16" class="indexterm"></a><p>

  993.     <code class="function">pg_read_file</code> returns part of a text file, starting

  994.     at the given <em class="parameter"><code>offset</code></em>, returning at most <em class="parameter"><code>length</code></em>

  995.     bytes (less if the end of file is reached first).  If <em class="parameter"><code>offset</code></em>

  996.     is negative, it is relative to the end of the file.

  997.     If <em class="parameter"><code>offset</code></em> and <em class="parameter"><code>length</code></em> are omitted, the entire

  998.     file is returned.  The bytes read from the file are interpreted as a string

  999.     in the server encoding; an error is thrown if they are not valid in that

  1000.     encoding.

  1001.    </p><a id="id-1.5.8.31.11.18" class="indexterm"></a><p>

  1002.     <code class="function">pg_read_binary_file</code> is similar to

  1003.     <code class="function">pg_read_file</code>, except that the result is a <code class="type">bytea</code> value;

  1004.     accordingly, no encoding checks are performed.

  1005.     In combination with the <code class="function">convert_from</code> function, this function

  1006.     can be used to read a file in a specified encoding:

  1007. </p><pre class="programlisting">

  1008. SELECT convert_from(pg_read_binary_file('file_in_utf8.txt'), 'UTF8');

  1009. </pre><p>

  1010.    </p><a id="id-1.5.8.31.11.20" class="indexterm"></a><p>

  1011.     <code class="function">pg_stat_file</code> returns a record containing the file

  1012.     size, last accessed time stamp, last modified time stamp,

  1013.     last file status change time stamp (Unix platforms only),

  1014.     file creation time stamp (Windows only), and a <code class="type">boolean</code>

  1015.     indicating if it is a directory.  Typical usages include:

  1016. </p><pre class="programlisting">

  1017. SELECT * FROM pg_stat_file('filename');

  1018. SELECT (pg_stat_file('filename')).modification;

  1019. </pre><p>

  1020.    </p></div><div class="sect2" id="FUNCTIONS-ADVISORY-LOCKS"><div class="titlepage"><div><div><h3 class="title">9.26.10. Advisory Lock Functions</h3></div></div></div><p>

  1021.     The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADVISORY-LOCKS-TABLE" title="Table 9.95. Advisory Lock Functions">Table 9.95</a>

  1022.     manage advisory locks.  For details about proper use of these functions,

  1023.     see <a class="xref" href="explicit-locking.html#ADVISORY-LOCKS" title="13.3.5. Advisory Locks">Section 13.3.5</a>.

  1024.    </p><div class="table" id="FUNCTIONS-ADVISORY-LOCKS-TABLE"><p class="title"><strong>Table 9.95. Advisory Lock Functions</strong></p><div class="table-contents"><table class="table" summary="Advisory Lock Functions" border="1"><colgroup><col /><col /><col /></colgroup><thead><tr><th>Name</th><th>Return Type</th><th>Description</th></tr></thead><tbody><tr><td>

  1025.         <code class="literal"><code class="function">pg_advisory_lock(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>

  1026.        </td><td><code class="type">void</code></td><td>Obtain exclusive session level advisory lock</td></tr><tr><td>

  1027.         <code class="literal"><code class="function">pg_advisory_lock(<em class="parameter"><code>key1</code></em> <code class="type">int</code>, <em class="parameter"><code>key2</code></em> <code class="type">int</code>)</code></code>

  1028.        </td><td><code class="type">void</code></td><td>Obtain exclusive session level advisory lock</td></tr><tr><td>

  1029.         <code class="literal"><code class="function">pg_advisory_lock_shared(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>

  1030.        </td><td><code class="type">void</code></td><td>Obtain shared session level advisory lock</td></tr><tr><td>

  1031.         <code class="literal"><code class="function">pg_advisory_lock_shared(<em class="parameter"><code>key1</code></em> <code class="type">int</code>, <em class="parameter"><code>key2</code></em> <code class="type">int</code>)</code></code>

  1032.        </td><td><code class="type">void</code></td><td>Obtain shared session level advisory lock</td></tr><tr><td>

  1033.         <code class="literal"><code class="function">pg_advisory_unlock(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>

  1034.        </td><td><code class="type">boolean</code></td><td>Release an exclusive session level advisory lock</td></tr><tr><td>

  1035.         <code class="literal"><code class="function">pg_advisory_unlock(<em class="parameter"><code>key1</code></em> <code class="type">int</code>, <em class="parameter"><code>key2</code></em> <code class="type">int</code>)</code></code>

  1036.        </td><td><code class="type">boolean</code></td><td>Release an exclusive session level advisory lock</td></tr><tr><td>

  1037.         <code class="literal"><code class="function">pg_advisory_unlock_all()</code></code>

  1038.        </td><td><code class="type">void</code></td><td>Release all session level advisory locks held by the current session</td></tr><tr><td>

  1039.         <code class="literal"><code class="function">pg_advisory_unlock_shared(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>

  1040.        </td><td><code class="type">boolean</code></td><td>Release a shared session level advisory lock</td></tr><tr><td>

  1041.         <code class="literal"><code class="function">pg_advisory_unlock_shared(<em class="parameter"><code>key1</code></em> <code class="type">int</code>, <em class="parameter"><code>key2</code></em> <code class="type">int</code>)</code></code>

  1042.        </td><td><code class="type">boolean</code></td><td>Release a shared session level advisory lock</td></tr><tr><td>

  1043.         <code class="literal"><code class="function">pg_advisory_xact_lock(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>

  1044.        </td><td><code class="type">void</code></td><td>Obtain exclusive transaction level advisory lock</td></tr><tr><td>

  1045.         <code class="literal"><code class="function">pg_advisory_xact_lock(<em class="parameter"><code>key1</code></em> <code class="type">int</code>, <em class="parameter"><code>key2</code></em> <code class="type">int</code>)</code></code>

  1046.        </td><td><code class="type">void</code></td><td>Obtain exclusive transaction level advisory lock</td></tr><tr><td>

  1047.         <code class="literal"><code class="function">pg_advisory_xact_lock_shared(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>

  1048.        </td><td><code class="type">void</code></td><td>Obtain shared transaction level advisory lock</td></tr><tr><td>

  1049.         <code class="literal"><code class="function">pg_advisory_xact_lock_shared(<em class="parameter"><code>key1</code></em> <code class="type">int</code>, <em class="parameter"><code>key2</code></em> <code class="type">int</code>)</code></code>

  1050.        </td><td><code class="type">void</code></td><td>Obtain shared transaction level advisory lock</td></tr><tr><td>

  1051.         <code class="literal"><code class="function">pg_try_advisory_lock(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>

  1052.        </td><td><code class="type">boolean</code></td><td>Obtain exclusive session level advisory lock if available</td></tr><tr><td>

  1053.         <code class="literal"><code class="function">pg_try_advisory_lock(<em class="parameter"><code>key1</code></em> <code class="type">int</code>, <em class="parameter"><code>key2</code></em> <code class="type">int</code>)</code></code>

  1054.        </td><td><code class="type">boolean</code></td><td>Obtain exclusive session level advisory lock if available</td></tr><tr><td>

  1055.         <code class="literal"><code class="function">pg_try_advisory_lock_shared(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>

  1056.        </td><td><code class="type">boolean</code></td><td>Obtain shared session level advisory lock if available</td></tr><tr><td>

  1057.         <code class="literal"><code class="function">pg_try_advisory_lock_shared(<em class="parameter"><code>key1</code></em> <code class="type">int</code>, <em class="parameter"><code>key2</code></em> <code class="type">int</code>)</code></code>

  1058.        </td><td><code class="type">boolean</code></td><td>Obtain shared session level advisory lock if available</td></tr><tr><td>

  1059.         <code class="literal"><code class="function">pg_try_advisory_xact_lock(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>

  1060.        </td><td><code class="type">boolean</code></td><td>Obtain exclusive transaction level advisory lock if available</td></tr><tr><td>

  1061.         <code class="literal"><code class="function">pg_try_advisory_xact_lock(<em class="parameter"><code>key1</code></em> <code class="type">int</code>, <em class="parameter"><code>key2</code></em> <code class="type">int</code>)</code></code>

  1062.        </td><td><code class="type">boolean</code></td><td>Obtain exclusive transaction level advisory lock if available</td></tr><tr><td>

  1063.         <code class="literal"><code class="function">pg_try_advisory_xact_lock_shared(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>

  1064.        </td><td><code class="type">boolean</code></td><td>Obtain shared transaction level advisory lock if available</td></tr><tr><td>

  1065.         <code class="literal"><code class="function">pg_try_advisory_xact_lock_shared(<em class="parameter"><code>key1</code></em> <code class="type">int</code>, <em class="parameter"><code>key2</code></em> <code class="type">int</code>)</code></code>

  1066.        </td><td><code class="type">boolean</code></td><td>Obtain shared transaction level advisory lock if available</td></tr></tbody></table></div></div><br class="table-break" /><a id="id-1.5.8.31.12.4" class="indexterm"></a><p>

  1067.     <code class="function">pg_advisory_lock</code> locks an application-defined resource,

  1068.     which can be identified either by a single 64-bit key value or two

  1069.     32-bit key values (note that these two key spaces do not overlap).

  1070.     If another session already holds a lock on the same resource identifier,

  1071.     this function will wait until the resource becomes available.  The lock

  1072.     is exclusive.  Multiple lock requests stack, so that if the same resource

  1073.     is locked three times it must then be unlocked three times to be

  1074.     released for other sessions' use.

  1075.    </p><a id="id-1.5.8.31.12.6" class="indexterm"></a><p>

  1076.     <code class="function">pg_advisory_lock_shared</code> works the same as

  1077.     <code class="function">pg_advisory_lock</code>,

  1078.     except the lock can be shared with other sessions requesting shared locks.

  1079.     Only would-be exclusive lockers are locked out.

  1080.    </p><a id="id-1.5.8.31.12.8" class="indexterm"></a><p>

  1081.     <code class="function">pg_try_advisory_lock</code> is similar to

  1082.     <code class="function">pg_advisory_lock</code>, except the function will not wait for the

  1083.     lock to become available.  It will either obtain the lock immediately and

  1084.     return <code class="literal">true</code>, or return <code class="literal">false</code> if the lock cannot be

  1085.     acquired immediately.

  1086.    </p><a id="id-1.5.8.31.12.10" class="indexterm"></a><p>

  1087.     <code class="function">pg_try_advisory_lock_shared</code> works the same as

  1088.     <code class="function">pg_try_advisory_lock</code>, except it attempts to acquire

  1089.     a shared rather than an exclusive lock.

  1090.    </p><a id="id-1.5.8.31.12.12" class="indexterm"></a><p>

  1091.     <code class="function">pg_advisory_unlock</code> will release a previously-acquired

  1092.     exclusive session level advisory lock.  It

  1093.     returns <code class="literal">true</code> if the lock is successfully released.

  1094.     If the lock was not held, it will return <code class="literal">false</code>,

  1095.     and in addition, an SQL warning will be reported by the server.

  1096.    </p><a id="id-1.5.8.31.12.14" class="indexterm"></a><p>

  1097.     <code class="function">pg_advisory_unlock_shared</code> works the same as

  1098.     <code class="function">pg_advisory_unlock</code>,

  1099.     except it releases a shared session level advisory lock.

  1100.    </p><a id="id-1.5.8.31.12.16" class="indexterm"></a><p>

  1101.     <code class="function">pg_advisory_unlock_all</code> will release all session level advisory

  1102.     locks held by the current session.  (This function is implicitly invoked

  1103.     at session end, even if the client disconnects ungracefully.)

  1104.    </p><a id="id-1.5.8.31.12.18" class="indexterm"></a><p>

  1105.     <code class="function">pg_advisory_xact_lock</code> works the same as

  1106.     <code class="function">pg_advisory_lock</code>, except the lock is automatically released

  1107.     at the end of the current transaction and cannot be released explicitly.

  1108.    </p><a id="id-1.5.8.31.12.20" class="indexterm"></a><p>

  1109.     <code class="function">pg_advisory_xact_lock_shared</code> works the same as

  1110.     <code class="function">pg_advisory_lock_shared</code>, except the lock is automatically released

  1111.     at the end of the current transaction and cannot be released explicitly.

  1112.    </p><a id="id-1.5.8.31.12.22" class="indexterm"></a><p>

  1113.     <code class="function">pg_try_advisory_xact_lock</code> works the same as

  1114.     <code class="function">pg_try_advisory_lock</code>, except the lock, if acquired,

  1115.     is automatically released at the end of the current transaction and

  1116.     cannot be released explicitly.

  1117.    </p><a id="id-1.5.8.31.12.24" class="indexterm"></a><p>

  1118.     <code class="function">pg_try_advisory_xact_lock_shared</code> works the same as

  1119.     <code class="function">pg_try_advisory_lock_shared</code>, except the lock, if acquired,

  1120.     is automatically released at the end of the current transaction and

  1121.     cannot be released explicitly.

  1122.    </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="functions-info.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="functions.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="functions-trigger.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">9.25. System Information Functions and Operators </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 9.27. Trigger Functions</td></tr></table></div></body></html>
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