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<!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 Vsnapshot" /><link rel="prev" href="functions-info.html" title="9.25. System Information Functions" /><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">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 11.5 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>
The functions described in this section are used to control and
monitor a <span class="productname">PostgreSQL</span> installation.
</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>
<a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-SET-TABLE" title="Table 9.77. Configuration Settings Functions">Table 9.77</a> shows the functions
available to query and alter run-time configuration parameters.
</p><div class="table" id="FUNCTIONS-ADMIN-SET-TABLE"><p class="title"><strong>Table 9.77. 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>
<a id="id-1.5.8.31.3.3.2.2.1.1.1" class="indexterm"></a>
<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>
</td><td><code class="type">text</code></td><td>get current value of setting</td></tr><tr><td>
<a id="id-1.5.8.31.3.3.2.2.2.1.1" class="indexterm"></a>
<code class="literal"><code class="function">set_config(<em class="parameter"><code>setting_name</code></em>,
<em class="parameter"><code>new_value</code></em>,
<em class="parameter"><code>is_local</code></em>)</code></code>
</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>
The function <code class="function">current_setting</code> yields the
current value of the setting <em class="parameter"><code>setting_name</code></em>.
It corresponds to the <acronym class="acronym">SQL</acronym> command
<code class="command">SHOW</code>. An example:
</p><pre class="programlisting">
SELECT current_setting('datestyle');
current_setting
-----------------
ISO, MDY
(1 row)
</pre><p>
If there is no setting named <em class="parameter"><code>setting_name</code></em>,
<code class="function">current_setting</code> throws an error
unless <em class="parameter"><code>missing_ok</code></em> is supplied and is
<code class="literal">true</code>.
</p><p>
<code class="function">set_config</code> sets the parameter
<em class="parameter"><code>setting_name</code></em> to
<em class="parameter"><code>new_value</code></em>. If
<em class="parameter"><code>is_local</code></em> is <code class="literal">true</code>, the
new value will only apply to the current transaction. If you want
the new value to apply for the current session, use
<code class="literal">false</code> instead. The function corresponds to the
SQL command <code class="command">SET</code>. An example:
</p><pre class="programlisting">
SELECT set_config('log_statement_stats', 'off', false);
set_config
------------
off
(1 row)
</pre><p>
</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>
The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-SIGNAL-TABLE" title="Table 9.78. Server Signaling Functions">Table 9.78</a> send control signals to
other server processes. Use of these functions is restricted to
superusers by default but access may be granted to others using
<code class="command">GRANT</code>, with noted exceptions.
</p><div class="table" id="FUNCTIONS-ADMIN-SIGNAL-TABLE"><p class="title"><strong>Table 9.78. 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>
<code class="literal"><code class="function">pg_cancel_backend(<em class="parameter"><code>pid</code></em> <code class="type">int</code>)</code></code>
</td><td><code class="type">boolean</code></td><td>Cancel a backend's current query. This is also allowed if the
calling role is a member of the role whose backend is being canceled or
the calling role has been granted <code class="literal">pg_signal_backend</code>,
however only superusers can cancel superuser backends.
</td></tr><tr><td>
<code class="literal"><code class="function">pg_reload_conf()</code></code>
</td><td><code class="type">boolean</code></td><td>Cause server processes to reload their configuration files</td></tr><tr><td>
<code class="literal"><code class="function">pg_rotate_logfile()</code></code>
</td><td><code class="type">boolean</code></td><td>Rotate server's log file</td></tr><tr><td>
<code class="literal"><code class="function">pg_terminate_backend(<em class="parameter"><code>pid</code></em> <code class="type">int</code>)</code></code>
</td><td><code class="type">boolean</code></td><td>Terminate a backend. This is also allowed if the calling role
is a member of the role whose backend is being terminated or the
calling role has been granted <code class="literal">pg_signal_backend</code>,
however only superusers can terminate superuser backends.
</td></tr></tbody></table></div></div><br class="table-break" /><p>
Each of these functions returns <code class="literal">true</code> if
successful and <code class="literal">false</code> otherwise.
</p><p>
<code class="function">pg_cancel_backend</code> and <code class="function">pg_terminate_backend</code>
send signals (<span class="systemitem">SIGINT</span> or <span class="systemitem">SIGTERM</span>
respectively) to backend processes identified by process ID.
The process ID of an active backend can be found from
the <code class="structfield">pid</code> column of the
<code class="structname">pg_stat_activity</code> view, or by listing the
<code class="command">postgres</code> processes on the server (using
<span class="application">ps</span> on Unix or the <span class="application">Task
Manager</span> on <span class="productname">Windows</span>).
The role of an active backend can be found from the
<code class="structfield">usename</code> column of the
<code class="structname">pg_stat_activity</code> view.
</p><p>
<code class="function">pg_reload_conf</code> sends a <span class="systemitem">SIGHUP</span> signal
to the server, causing configuration files
to be reloaded by all server processes.
</p><p>
<code class="function">pg_rotate_logfile</code> signals the log-file manager to switch
to a new output file immediately. This works only when the built-in
log collector is running, since otherwise there is no log-file manager
subprocess.
</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>
The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-BACKUP-TABLE" title="Table 9.79. Backup Control Functions">Table 9.79</a> assist in making on-line backups.
These functions cannot be executed during recovery (except
non-exclusive <code class="function">pg_start_backup</code>,
non-exclusive <code class="function">pg_stop_backup</code>,
<code class="function">pg_is_in_backup</code>, <code class="function">pg_backup_start_time</code>
and <code class="function">pg_wal_lsn_diff</code>).
</p><div class="table" id="FUNCTIONS-ADMIN-BACKUP-TABLE"><p class="title"><strong>Table 9.79. 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>
<code class="literal"><code class="function">pg_create_restore_point(<em class="parameter"><code>name</code></em> <code class="type">text</code>)</code></code>
</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>
<code class="literal"><code class="function">pg_current_wal_flush_lsn()</code></code>
</td><td><code class="type">pg_lsn</code></td><td>Get current write-ahead log flush location</td></tr><tr><td>
<code class="literal"><code class="function">pg_current_wal_insert_lsn()</code></code>
</td><td><code class="type">pg_lsn</code></td><td>Get current write-ahead log insert location</td></tr><tr><td>
<code class="literal"><code class="function">pg_current_wal_lsn()</code></code>
</td><td><code class="type">pg_lsn</code></td><td>Get current write-ahead log write location</td></tr><tr><td>
<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>
</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>
<code class="literal"><code class="function">pg_stop_backup()</code></code>
</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>
<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>
</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>
<code class="literal"><code class="function">pg_is_in_backup()</code></code>
</td><td><code class="type">bool</code></td><td>True if an on-line exclusive backup is still in progress.</td></tr><tr><td>
<code class="literal"><code class="function">pg_backup_start_time()</code></code>
</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>
<code class="literal"><code class="function">pg_switch_wal()</code></code>
</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>
<code class="literal"><code class="function">pg_walfile_name(<em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>)</code></code>
</td><td><code class="type">text</code></td><td>Convert write-ahead log location to file name</td></tr><tr><td>
<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>
</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>
<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>
</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>
<code class="function">pg_start_backup</code> accepts an arbitrary user-defined label for
the backup. (Typically this would be the name under which the backup dump
file will be stored.) When used in exclusive mode, the function writes a
backup label file (<code class="filename">backup_label</code>) and, if there are any links
in the <code class="filename">pg_tblspc/</code> directory, a tablespace map file
(<code class="filename">tablespace_map</code>) into the database cluster's data directory,
performs a checkpoint, and then returns the backup's starting write-ahead
log location as text. The user can ignore this result value, but it is
provided in case it is useful. When used in non-exclusive mode, the
contents of these files are instead returned by the
<code class="function">pg_stop_backup</code> function, and should be written to the backup
by the caller.
</p><pre class="programlisting">
postgres=# select pg_start_backup('label_goes_here');
pg_start_backup
-----------------
0/D4445B8
(1 row)
</pre><p>
There is an optional second parameter of type <code class="type">boolean</code>. If <code class="literal">true</code>,
it specifies executing <code class="function">pg_start_backup</code> as quickly as
possible. This forces an immediate checkpoint which will cause a
spike in I/O operations, slowing any concurrently executing queries.
</p><p>
In an exclusive backup, <code class="function">pg_stop_backup</code> removes the label file
and, if it exists, the <code class="filename">tablespace_map</code> file created by
<code class="function">pg_start_backup</code>. In a non-exclusive backup, the contents of
the <code class="filename">backup_label</code> and <code class="filename">tablespace_map</code> are returned
in the result of the function, and should be written to files in the
backup (and not in the data directory). There is an optional second
parameter of type <code class="type">boolean</code>. If false, the <code class="function">pg_stop_backup</code>
will return immediately after the backup is completed without waiting for
WAL to be archived. This behavior is only useful for backup
software which independently monitors WAL archiving. Otherwise, WAL
required to make the backup consistent might be missing and make the backup
useless. When this parameter is set to true, <code class="function">pg_stop_backup</code>
will wait for WAL to be archived when archiving is enabled; on the standby,
this means that it will wait only when <code class="varname">archive_mode = always</code>.
If write activity on the primary is low, it may be useful to run
<code class="function">pg_switch_wal</code> on the primary in order to trigger
an immediate segment switch.
</p><p>
When executed on a primary, the function also creates a backup history file
in the write-ahead log
archive area. The history file includes the label given to
<code class="function">pg_start_backup</code>, the starting and ending write-ahead log locations for
the backup, and the starting and ending times of the backup. The return
value is the backup's ending write-ahead log location (which again
can be ignored). After recording the ending location, the current
write-ahead log insertion
point is automatically advanced to the next write-ahead log file, so that the
ending write-ahead log file can be archived immediately to complete the backup.
</p><p>
<code class="function">pg_switch_wal</code> moves to the next write-ahead log file, allowing the
current file to be archived (assuming you are using continuous archiving).
The return value is the ending write-ahead log location + 1 within the just-completed write-ahead log file.
If there has been no write-ahead log activity since the last write-ahead log switch,
<code class="function">pg_switch_wal</code> does nothing and returns the start location
of the write-ahead log file currently in use.
</p><p>
<code class="function">pg_create_restore_point</code> creates a named write-ahead log
record that can be used as recovery target, and returns the corresponding
write-ahead log location. The given name can then be used with
<a class="xref" href="recovery-target-settings.html#RECOVERY-TARGET-NAME">recovery_target_name</a> to specify the point up to which
recovery will proceed. Avoid creating multiple restore points with the
same name, since recovery will stop at the first one whose name matches
the recovery target.
</p><p>
<code class="function">pg_current_wal_lsn</code> displays the current write-ahead log write
location in the same format used by the above functions. Similarly,
<code class="function">pg_current_wal_insert_lsn</code> displays the current write-ahead log
insertion location and <code class="function">pg_current_wal_flush_lsn</code> displays the
current write-ahead log flush location. The insertion location is the <span class="quote">“<span class="quote">logical</span>”</span>
end of the write-ahead log at any instant, while the write location is the end of
what has actually been written out from the server's internal buffers and flush
location is the location guaranteed to be written to durable storage. The write
location is the end of what can be examined from outside the server, and is usually
what you want if you are interested in archiving partially-complete write-ahead log
files. The insertion and flush locations are made available primarily for server
debugging purposes. These are both read-only operations and do not
require superuser permissions.
</p><p>
You can use <code class="function">pg_walfile_name_offset</code> to extract the
corresponding write-ahead log file name and byte offset from the results of any of the
above functions. For example:
</p><pre class="programlisting">
postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
file_name | file_offset
--------------------------+-------------
00000001000000000000000D | 4039624
(1 row)
</pre><p>
Similarly, <code class="function">pg_walfile_name</code> extracts just the write-ahead log file name.
When the given write-ahead log location is exactly at a write-ahead log file boundary, both
these functions return the name of the preceding write-ahead log file.
This is usually the desired behavior for managing write-ahead log archiving
behavior, since the preceding file is the last one that currently
needs to be archived.
</p><p>
<code class="function">pg_wal_lsn_diff</code> calculates the difference in bytes
between two write-ahead log locations. It can be used with
<code class="structname">pg_stat_replication</code> or some functions shown in
<a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-BACKUP-TABLE" title="Table 9.79. Backup Control Functions">Table 9.79</a> to get the replication lag.
</p><p>
For details about proper usage of these functions, see
<a class="xref" href="continuous-archiving.html" title="25.3. Continuous Archiving and Point-in-Time Recovery (PITR)">Section 25.3</a>.
</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>
The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-RECOVERY-INFO-TABLE" title="Table 9.80. Recovery Information Functions">Table 9.80</a> provide information
about the current status of the standby.
These functions may be executed both during recovery and in normal running.
</p><div class="table" id="FUNCTIONS-RECOVERY-INFO-TABLE"><p class="title"><strong>Table 9.80. 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>
<code class="literal"><code class="function">pg_is_in_recovery()</code></code>
</td><td><code class="type">bool</code></td><td>True if recovery is still in progress.
</td></tr><tr><td>
<code class="literal"><code class="function">pg_last_wal_receive_lsn()</code></code>
</td><td><code class="type">pg_lsn</code></td><td>Get last write-ahead log location received and synced to disk by
streaming replication. While streaming replication is in progress
this will increase monotonically. If recovery has completed this will
remain static at
the value of the last WAL record received and synced to disk during
recovery. If streaming replication is disabled, or if it has not yet
started, the function returns NULL.
</td></tr><tr><td>
<code class="literal"><code class="function">pg_last_wal_replay_lsn()</code></code>
</td><td><code class="type">pg_lsn</code></td><td>Get last write-ahead log location replayed during recovery.
If recovery is still in progress this will increase monotonically.
If recovery has completed then this value will remain static at
the value of the last WAL record applied during that recovery.
When the server has been started normally without recovery
the function returns NULL.
</td></tr><tr><td>
<code class="literal"><code class="function">pg_last_xact_replay_timestamp()</code></code>
</td><td><code class="type">timestamp with time zone</code></td><td>Get time stamp of last transaction replayed during recovery.
This is the time at which the commit or abort WAL record for that
transaction was generated on the primary.
If no transactions have been replayed during recovery, this function
returns NULL. Otherwise, if recovery is still in progress this will
increase monotonically. If recovery has completed then this value will
remain static at the value of the last transaction applied during that
recovery. When the server has been started normally without recovery
the function returns NULL.
</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><p>
The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-RECOVERY-CONTROL-TABLE" title="Table 9.81. Recovery Control Functions">Table 9.81</a> control the progress of recovery.
These functions may be executed only during recovery.
</p><div class="table" id="FUNCTIONS-RECOVERY-CONTROL-TABLE"><p class="title"><strong>Table 9.81. 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>
<code class="literal"><code class="function">pg_is_wal_replay_paused()</code></code>
</td><td><code class="type">bool</code></td><td>True if recovery is paused.
</td></tr><tr><td>
<code class="literal"><code class="function">pg_wal_replay_pause()</code></code>
</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).
</td></tr><tr><td>
<code class="literal"><code class="function">pg_wal_replay_resume()</code></code>
</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).
</td></tr></tbody></table></div></div><br class="table-break" /><p>
While recovery is paused no further database changes are applied.
If in hot standby, all new queries will see the same consistent snapshot
of the database, and no further query conflicts will be generated until
recovery is resumed.
</p><p>
If streaming replication is disabled, the paused state may continue
indefinitely without problem. While streaming replication is in
progress WAL records will continue to be received, which will
eventually fill available disk space, depending upon the duration of
the pause, the rate of WAL generation and available disk space.
</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>
<span class="productname">PostgreSQL</span> allows database sessions to synchronize their
snapshots. A <em class="firstterm">snapshot</em> determines which data is visible to the
transaction that is using the snapshot. Synchronized snapshots are
necessary when two or more sessions need to see identical content in the
database. If two sessions just start their transactions independently,
there is always a possibility that some third transaction commits
between the executions of the two <code class="command">START TRANSACTION</code> commands,
so that one session sees the effects of that transaction and the other
does not.
</p><p>
To solve this problem, <span class="productname">PostgreSQL</span> allows a transaction to
<em class="firstterm">export</em> the snapshot it is using. As long as the exporting
transaction remains open, other transactions can <em class="firstterm">import</em> its
snapshot, and thereby be guaranteed that they see exactly the same view
of the database that the first transaction sees. But note that any
database changes made by any one of these transactions remain invisible
to the other transactions, as is usual for changes made by uncommitted
transactions. So the transactions are synchronized with respect to
pre-existing data, but act normally for changes they make themselves.
</p><p>
Snapshots are exported with the <code class="function">pg_export_snapshot</code> function,
shown in <a class="xref" href="functions-admin.html#FUNCTIONS-SNAPSHOT-SYNCHRONIZATION-TABLE" title="Table 9.82. Snapshot Synchronization Functions">Table 9.82</a>, and
imported with the <a class="xref" href="sql-set-transaction.html" title="SET TRANSACTION"><span class="refentrytitle">SET TRANSACTION</span></a> command.
</p><div class="table" id="FUNCTIONS-SNAPSHOT-SYNCHRONIZATION-TABLE"><p class="title"><strong>Table 9.82. 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>
<code class="literal"><code class="function">pg_export_snapshot()</code></code>
</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>
The function <code class="function">pg_export_snapshot</code> saves the current snapshot
and returns a <code class="type">text</code> string identifying the snapshot. This string
must be passed (outside the database) to clients that want to import the
snapshot. The snapshot is available for import only until the end of the
transaction that exported it. A transaction can export more than one
snapshot, if needed. Note that doing so is only useful in <code class="literal">READ
COMMITTED</code> transactions, since in <code class="literal">REPEATABLE READ</code> and
higher isolation levels, transactions use the same snapshot throughout
their lifetime. Once a transaction has exported any snapshots, it cannot
be prepared with <a class="xref" href="sql-prepare-transaction.html" title="PREPARE TRANSACTION"><span class="refentrytitle">PREPARE TRANSACTION</span></a>.
</p><p>
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
exported snapshot.
</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>
The functions shown
in <a class="xref" href="functions-admin.html#FUNCTIONS-REPLICATION-TABLE" title="Table 9.83. Replication SQL Functions">Table 9.83</a> are for
controlling and interacting with replication features.
See <a class="xref" href="warm-standby.html#STREAMING-REPLICATION" title="26.2.5. Streaming Replication">Section 26.2.5</a>,
<a class="xref" href="warm-standby.html#STREAMING-REPLICATION-SLOTS" title="26.2.6. Replication Slots">Section 26.2.6</a>, and
<a class="xref" href="replication-origins.html" title="Chapter 50. Replication Progress Tracking">Chapter 50</a>
for information about the underlying features.
Use of functions for replication origin is restricted to superusers.
Use of functions for replication slot is restricted to superusers
and users having <code class="literal">REPLICATION</code> privilege.
</p><p>
Many of these functions have equivalent commands in the replication
protocol; see <a class="xref" href="protocol-replication.html" title="53.4. Streaming Replication Protocol">Section 53.4</a>.
</p><p>
The functions described in
<a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-BACKUP" title="9.26.3. Backup Control Functions">Section 9.26.3</a>,
<a class="xref" href="functions-admin.html#FUNCTIONS-RECOVERY-CONTROL" title="9.26.4. Recovery Control Functions">Section 9.26.4</a>, and
<a class="xref" href="functions-admin.html#FUNCTIONS-SNAPSHOT-SYNCHRONIZATION" title="9.26.5. Snapshot Synchronization Functions">Section 9.26.5</a>
are also relevant for replication.
</p><div class="table" id="FUNCTIONS-REPLICATION-TABLE"><p class="title"><strong>Table 9.83. 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>
<a id="id-1.5.8.31.8.5.2.2.1.1.1" class="indexterm"></a>
<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>
</td><td>
(<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>)
</td><td>
Creates a new physical replication slot named
<em class="parameter"><code>slot_name</code></em>. The optional second parameter,
when <code class="literal">true</code>, specifies that the <acronym class="acronym">LSN</acronym> for this
replication slot be reserved immediately; otherwise
the <acronym class="acronym">LSN</acronym> is reserved on first connection from a streaming
replication client. Streaming changes from a physical slot is only
possible with the streaming-replication protocol —
see <a class="xref" href="protocol-replication.html" title="53.4. Streaming Replication Protocol">Section 53.4</a>. The optional third
parameter, <em class="parameter"><code>temporary</code></em>, when set to true, specifies that
the slot should not be permanently stored to disk and is only meant
for use by current session. Temporary slots are also
released upon any error. This function corresponds
to the replication protocol command <code class="literal">CREATE_REPLICATION_SLOT
... PHYSICAL</code>.
</td></tr><tr><td>
<a id="id-1.5.8.31.8.5.2.2.2.1.1" class="indexterm"></a>
<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>
</td><td>
<code class="type">void</code>
</td><td>
Drops the physical or logical replication slot
named <em class="parameter"><code>slot_name</code></em>. Same as replication protocol
command <code class="literal">DROP_REPLICATION_SLOT</code>. For logical slots, this must
be called when connected to the same database the slot was created on.
</td></tr><tr><td>
<a id="id-1.5.8.31.8.5.2.2.3.1.1" class="indexterm"></a>
<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>
</td><td>
(<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>)
</td><td>
Creates a new logical (decoding) replication slot named
<em class="parameter"><code>slot_name</code></em> using the output plugin
<em class="parameter"><code>plugin</code></em>. The optional third
parameter, <em class="parameter"><code>temporary</code></em>, when set to true, specifies that
the slot should not be permanently stored to disk and is only meant
for use by current session. Temporary slots are also
released upon any error. A call to this function has the same
effect as the replication protocol command
<code class="literal">CREATE_REPLICATION_SLOT ... LOGICAL</code>.
</td></tr><tr><td>
<a id="id-1.5.8.31.8.5.2.2.4.1.1" class="indexterm"></a>
<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>
</td><td>
(<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>)
</td><td>
Returns changes in the slot <em class="parameter"><code>slot_name</code></em>, starting
from the point at which since changes have been consumed last. If
<em class="parameter"><code>upto_lsn</code></em> and <em class="parameter"><code>upto_nchanges</code></em> are NULL,
logical decoding will continue until end of WAL. If
<em class="parameter"><code>upto_lsn</code></em> is non-NULL, decoding will include only
those transactions which commit prior to the specified LSN. If
<em class="parameter"><code>upto_nchanges</code></em> is non-NULL, decoding will
stop when the number of rows produced by decoding exceeds
the specified value. Note, however, that the actual number of
rows returned may be larger, since this limit is only checked after
adding the rows produced when decoding each new transaction commit.
</td></tr><tr><td>
<a id="id-1.5.8.31.8.5.2.2.5.1.1" class="indexterm"></a>
<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>
</td><td>
(<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>)
</td><td>
Behaves just like
the <code class="function">pg_logical_slot_get_changes()</code> function,
except that changes are not consumed; that is, they will be returned
again on future calls.
</td></tr><tr><td>
<a id="id-1.5.8.31.8.5.2.2.6.1.1" class="indexterm"></a>
<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>
</td><td>
(<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>)
</td><td>
Behaves just like
the <code class="function">pg_logical_slot_get_changes()</code> function,
except that changes are returned as <code class="type">bytea</code>.
</td></tr><tr><td>
<a id="id-1.5.8.31.8.5.2.2.7.1.1" class="indexterm"></a>
<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>
</td><td>
(<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>)
</td><td>
Behaves just like
the <code class="function">pg_logical_slot_get_changes()</code> function,
except that changes are returned as <code class="type">bytea</code> and that
changes are not consumed; that is, they will be returned again
on future calls.
</td></tr><tr><td>
<a id="id-1.5.8.31.8.5.2.2.8.1.1" class="indexterm"></a>
<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>
</td><td>
(<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>)
<code class="type">bool</code>
</td><td>
Advances the current confirmed position of a replication slot named
<em class="parameter"><code>slot_name</code></em>. The slot will not be moved backwards,
and it will not be moved beyond the current insert location. Returns
name of the slot and real position to which it was advanced to.
</td></tr><tr><td id="PG-REPLICATION-ORIGIN-CREATE">
<a id="id-1.5.8.31.8.5.2.2.9.1.1" class="indexterm"></a>
<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>
</td><td>
<code class="type">oid</code>
</td><td>
Create a replication origin with the given external
name, and return the internal id assigned to it.
</td></tr><tr><td id="PG-REPLICATION-ORIGIN-DROP">
<a id="id-1.5.8.31.8.5.2.2.10.1.1" class="indexterm"></a>
<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>
</td><td>
<code class="type">void</code>
</td><td>
Delete a previously created replication origin, including any
associated replay progress.
</td></tr><tr><td>
<a id="id-1.5.8.31.8.5.2.2.11.1.1" class="indexterm"></a>
<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>
</td><td>
<code class="type">oid</code>
</td><td>
Lookup a replication origin by name and return the internal id. If no
corresponding replication origin is found an error is thrown.
</td></tr><tr><td id="PG-REPLICATION-ORIGIN-SESSION-SETUP">
<a id="id-1.5.8.31.8.5.2.2.12.1.1" class="indexterm"></a>
<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>
</td><td>
<code class="type">void</code>
</td><td>
Mark the current session as replaying from the given
origin, allowing replay progress to be tracked. Use
<code class="function">pg_replication_origin_session_reset</code> to revert.
Can only be used if no previous origin is configured.
</td></tr><tr><td>
<a id="id-1.5.8.31.8.5.2.2.13.1.1" class="indexterm"></a>
<code class="literal"><code class="function">pg_replication_origin_session_reset()</code></code>
</td><td>
<code class="type">void</code>
</td><td>
Cancel the effects
of <code class="function">pg_replication_origin_session_setup()</code>.
</td></tr><tr><td>
<a id="id-1.5.8.31.8.5.2.2.14.1.1" class="indexterm"></a>
<code class="literal"><code class="function">pg_replication_origin_session_is_setup()</code></code>
</td><td>
<code class="type">bool</code>
</td><td>
Has a replication origin been configured in the current session?
</td></tr><tr><td id="PG-REPLICATION-ORIGIN-SESSION-PROGRESS">
<a id="id-1.5.8.31.8.5.2.2.15.1.1" class="indexterm"></a>
<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>
</td><td>
<code class="type">pg_lsn</code>
</td><td>
Return the replay location for the replication origin configured in
the current session. The parameter <em class="parameter"><code>flush</code></em>
determines whether the corresponding local transaction will be
guaranteed to have been flushed to disk or not.
</td></tr><tr><td id="PG-REPLICATION-ORIGIN-XACT-SETUP">
<a id="id-1.5.8.31.8.5.2.2.16.1.1" class="indexterm"></a>
<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>
</td><td>
<code class="type">void</code>
</td><td>
Mark the current transaction as replaying a transaction that has
committed at the given <acronym class="acronym">LSN</acronym> and timestamp. Can
only be called when a replication origin has previously been
configured using
<code class="function">pg_replication_origin_session_setup()</code>.
</td></tr><tr><td id="PG-REPLICATION-ORIGIN-XACT-RESET">
<a id="id-1.5.8.31.8.5.2.2.17.1.1" class="indexterm"></a>
<code class="literal"><code class="function">pg_replication_origin_xact_reset()</code></code>
</td><td>
<code class="type">void</code>
</td><td>
Cancel the effects of
<code class="function">pg_replication_origin_xact_setup()</code>.
</td></tr><tr><td id="PG-REPLICATION-ORIGIN-ADVANCE">
<a id="id-1.5.8.31.8.5.2.2.18.1.1" class="indexterm"></a>
<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>
</td><td>
<code class="type">void</code>
</td><td>
Set replication progress for the given node to the given
location. This primarily is useful for setting up the initial location
or a new location after configuration changes and similar. Be aware
that careless use of this function can lead to inconsistently
replicated data.
</td></tr><tr><td id="PG-REPLICATION-ORIGIN-PROGRESS">
<a id="id-1.5.8.31.8.5.2.2.19.1.1" class="indexterm"></a>
<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>
</td><td>
<code class="type">pg_lsn</code>
</td><td>
Return the replay location for the given replication origin. The
parameter <em class="parameter"><code>flush</code></em> determines whether the
corresponding local transaction will be guaranteed to have been
flushed to disk or not.
</td></tr><tr><td id="PG-LOGICAL-EMIT-MESSAGE-TEXT">
<a id="id-1.5.8.31.8.5.2.2.20.1.1" class="indexterm"></a>
<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>
</td><td>
<code class="type">pg_lsn</code>
</td><td>
Emit text logical decoding message. This can be used to pass generic
messages to logical decoding plugins through WAL. The parameter
<em class="parameter"><code>transactional</code></em> specifies if the message should
be part of current transaction or if it should be written immediately
and decoded as soon as the logical decoding reads the record. The
<em class="parameter"><code>prefix</code></em> is textual prefix used by the logical
decoding plugins to easily recognize interesting messages for them.
The <em class="parameter"><code>content</code></em> is the text of the message.
</td></tr><tr><td id="PG-LOGICAL-EMIT-MESSAGE-BYTEA">
<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>
</td><td>
<code class="type">pg_lsn</code>
</td><td>
Emit binary logical decoding message. This can be used to pass generic
messages to logical decoding plugins through WAL. The parameter
<em class="parameter"><code>transactional</code></em> specifies if the message should
be part of current transaction or if it should be written immediately
and decoded as soon as the logical decoding reads the record. The
<em class="parameter"><code>prefix</code></em> is textual prefix used by the logical
decoding plugins to easily recognize interesting messages for them.
The <em class="parameter"><code>content</code></em> is the binary content of the
message.
</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>
The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-DBSIZE" title="Table 9.84. Database Object Size Functions">Table 9.84</a> calculate
the disk space usage of database objects.
</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 9.84. 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>
<code class="literal"><code class="function">pg_database_size(<code class="type">oid</code>)</code></code>
</td><td><code class="type">bigint</code></td><td>Disk space used by the database with the specified OID</td></tr><tr><td>
<code class="literal"><code class="function">pg_database_size(<code class="type">name</code>)</code></code>
</td><td><code class="type">bigint</code></td><td>Disk space used by the database with the specified name</td></tr><tr><td>
<code class="literal"><code class="function">pg_indexes_size(<code class="type">regclass</code>)</code></code>
</td><td><code class="type">bigint</code></td><td>
Total disk space used by indexes attached to the specified table
</td></tr><tr><td>
<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>
</td><td><code class="type">bigint</code></td><td>
Disk space used by the specified fork (<code class="literal">'main'</code>,
<code class="literal">'fsm'</code>, <code class="literal">'vm'</code>, or <code class="literal">'init'</code>)
of the specified table or index
</td></tr><tr><td>
<code class="literal"><code class="function">pg_relation_size(<em class="parameter"><code>relation</code></em> <code class="type">regclass</code>)</code></code>
</td><td><code class="type">bigint</code></td><td>
Shorthand for <code class="literal">pg_relation_size(..., 'main')</code>
</td></tr><tr><td>
<code class="literal"><code class="function">pg_size_bytes(<code class="type">text</code>)</code></code>
</td><td><code class="type">bigint</code></td><td>
Converts a size in human-readable format with size units into bytes
</td></tr><tr><td>
<code class="literal"><code class="function">pg_size_pretty(<code class="type">bigint</code>)</code></code>
</td><td><code class="type">text</code></td><td>
Converts a size in bytes expressed as a 64-bit integer into a
human-readable format with size units
</td></tr><tr><td>
<code class="literal"><code class="function">pg_size_pretty(<code class="type">numeric</code>)</code></code>
</td><td><code class="type">text</code></td><td>
Converts a size in bytes expressed as a numeric value into a
human-readable format with size units
</td></tr><tr><td>
<code class="literal"><code class="function">pg_table_size(<code class="type">regclass</code>)</code></code>
</td><td><code class="type">bigint</code></td><td>
Disk space used by the specified table, excluding indexes
(but including TOAST, free space map, and visibility map)
</td></tr><tr><td>
<code class="literal"><code class="function">pg_tablespace_size(<code class="type">oid</code>)</code></code>
</td><td><code class="type">bigint</code></td><td>Disk space used by the tablespace with the specified OID</td></tr><tr><td>
<code class="literal"><code class="function">pg_tablespace_size(<code class="type">name</code>)</code></code>
</td><td><code class="type">bigint</code></td><td>Disk space used by the tablespace with the specified name</td></tr><tr><td>
<code class="literal"><code class="function">pg_total_relation_size(<code class="type">regclass</code>)</code></code>
</td><td><code class="type">bigint</code></td><td>
Total disk space used by the specified table,
including all indexes and <acronym class="acronym">TOAST</acronym> data
</td></tr></tbody></table></div></div><br class="table-break" /><p>
<code class="function">pg_column_size</code> shows the space used to store any individual
data value.
</p><p>
<code class="function">pg_total_relation_size</code> accepts the OID or name of a
table or toast table, and returns the total on-disk space used for
that table, including all associated indexes. This function is
equivalent to <code class="function">pg_table_size</code>
<code class="literal">+</code> <code class="function">pg_indexes_size</code>.
</p><p>
<code class="function">pg_table_size</code> accepts the OID or name of a table and
returns the disk space needed for that table, exclusive of indexes.
(TOAST space, free space map, and visibility map are included.)
</p><p>
<code class="function">pg_indexes_size</code> accepts the OID or name of a table and
returns the total disk space used by all the indexes attached to that
table.
</p><p>
<code class="function">pg_database_size</code> and <code class="function">pg_tablespace_size</code>
accept the OID or name of a database or tablespace, and return the total
disk space used therein. To use <code class="function">pg_database_size</code>,
you must have <code class="literal">CONNECT</code> permission on the specified database
(which is granted by default), or be a member of the <code class="literal">pg_read_all_stats</code>
role. To use <code class="function">pg_tablespace_size</code>, you must have
<code class="literal">CREATE</code> permission on the specified tablespace, or be a member
of the <code class="literal">pg_read_all_stats</code> role unless it is the default tablespace for
the current database.
</p><p>
<code class="function">pg_relation_size</code> accepts the OID or name of a table, index
or toast table, and returns the on-disk size in bytes of one fork of
that relation. (Note that for most purposes it is more convenient to
use the higher-level functions <code class="function">pg_total_relation_size</code>
or <code class="function">pg_table_size</code>, which sum the sizes of all forks.)
With one argument, it returns the size of the main data fork of the
relation. The second argument can be provided to specify which fork
to examine:
</p><div class="itemizedlist"><ul class="itemizedlist compact" style="list-style-type: disc; "><li class="listitem"><p>
<code class="literal">'main'</code> returns the size of the main
data fork of the relation.
</p></li><li class="listitem"><p>
<code class="literal">'fsm'</code> returns the size of the Free Space Map
(see <a class="xref" href="storage-fsm.html" title="68.3. Free Space Map">Section 68.3</a>) associated with the relation.
</p></li><li class="listitem"><p>
<code class="literal">'vm'</code> returns the size of the Visibility Map
(see <a class="xref" href="storage-vm.html" title="68.4. Visibility Map">Section 68.4</a>) associated with the relation.
</p></li><li class="listitem"><p>
<code class="literal">'init'</code> returns the size of the initialization
fork, if any, associated with the relation.
</p></li></ul></div><p>
</p><p>
<code class="function">pg_size_pretty</code> can be used to format the result of one of
the other functions in a human-readable way, using bytes, kB, MB, GB or TB
as appropriate.
</p><p>
<code class="function">pg_size_bytes</code> can be used to get the size in bytes from a
string in human-readable format. The input may have units of bytes, kB,
MB, GB or TB, and is parsed case-insensitively. If no units are specified,
bytes are assumed.
</p><div class="note"><h3 class="title">Note</h3><p>
The units kB, MB, GB and TB used by the functions
<code class="function">pg_size_pretty</code> and <code class="function">pg_size_bytes</code> are defined
using powers of 2 rather than powers of 10, so 1kB is 1024 bytes, 1MB is
1024<sup>2</sup> = 1048576 bytes, and so on.
</p></div><p>
The functions above that operate on tables or indexes accept a
<code class="type">regclass</code> argument, which is simply the OID of the table or index
in the <code class="structname">pg_class</code> system catalog. You do not have to look up
the OID by hand, however, since the <code class="type">regclass</code> data type's input
converter will do the work for you. Just write the table name enclosed in
single quotes so that it looks like a literal constant. For compatibility
with the handling of ordinary <acronym class="acronym">SQL</acronym> names, the string
will be converted to lower case unless it contains double quotes around
the table name.
</p><p>
If an OID that does not represent an existing object is passed as
argument to one of the above functions, NULL is returned.
</p><p>
The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-DBLOCATION" title="Table 9.85. Database Object Location Functions">Table 9.85</a> assist
in identifying the specific disk files associated with database objects.
</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 9.85. 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>
<code class="literal"><code class="function">pg_relation_filenode(<em class="parameter"><code>relation</code></em> <code class="type">regclass</code>)</code></code>
</td><td><code class="type">oid</code></td><td>
Filenode number of the specified relation
</td></tr><tr><td>
<code class="literal"><code class="function">pg_relation_filepath(<em class="parameter"><code>relation</code></em> <code class="type">regclass</code>)</code></code>
</td><td><code class="type">text</code></td><td>
File path name of the specified relation
</td></tr><tr><td>
<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>
</td><td><code class="type">regclass</code></td><td>
Find the relation associated with a given tablespace and filenode
</td></tr></tbody></table></div></div><br class="table-break" /><p>
<code class="function">pg_relation_filenode</code> accepts the OID or name of a table,
index, sequence, or toast table, and returns the <span class="quote">“<span class="quote">filenode</span>”</span> number
currently assigned to it. The filenode is the base component of the file
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>
for more information). For most tables the result is the same as
<code class="structname">pg_class</code>.<code class="structfield">relfilenode</code>, but for certain
system catalogs <code class="structfield">relfilenode</code> is zero and this function must
be used to get the correct value. The function returns NULL if passed
a relation that does not have storage, such as a view.
</p><p>
<code class="function">pg_relation_filepath</code> is similar to
<code class="function">pg_relation_filenode</code>, but it returns the entire file path name
(relative to the database cluster's data directory <code class="varname">PGDATA</code>) of
the relation.
</p><p>
<code class="function">pg_filenode_relation</code> is the reverse of
<code class="function">pg_relation_filenode</code>. Given a <span class="quote">“<span class="quote">tablespace</span>”</span> OID and
a <span class="quote">“<span class="quote">filenode</span>”</span>, it returns the associated relation's OID. For a table
in the database's default tablespace, the tablespace can be specified as 0.
</p><p>
<a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-COLLATION" title="Table 9.86. Collation Management Functions">Table 9.86</a> lists functions used to manage
collations.
</p><div class="table" id="FUNCTIONS-ADMIN-COLLATION"><p class="title"><strong>Table 9.86. 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>
<a id="id-1.5.8.31.9.33.2.2.1.1.1" class="indexterm"></a>
<code class="literal"><code class="function">pg_collation_actual_version(<code class="type">oid</code>)</code></code>
</td><td><code class="type">text</code></td><td>Return actual version of collation from operating system</td></tr><tr><td>
<a id="id-1.5.8.31.9.33.2.2.2.1.1" class="indexterm"></a>
<code class="literal"><code class="function">pg_import_system_collations(<em class="parameter"><code>schema</code></em> <code class="type">regnamespace</code>)</code></code>
</td><td><code class="type">integer</code></td><td>Import operating system collations</td></tr></tbody></table></div></div><br class="table-break" /><p>
<code class="function">pg_collation_actual_version</code> returns the actual
version of the collation object as it is currently installed in the
operating system. If this is different from the value
in <code class="literal">pg_collation.collversion</code>, then objects depending on
the collation might need to be rebuilt. See also
<a class="xref" href="sql-altercollation.html" title="ALTER COLLATION"><span class="refentrytitle">ALTER COLLATION</span></a>.
</p><p>
<code class="function">pg_import_system_collations</code> adds collations to the system
catalog <code class="literal">pg_collation</code> based on all the
locales it finds in the operating system. This is
what <code class="command">initdb</code> uses;
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
locales are installed into the operating system later on, this function
can be run again to add collations for the new locales. Locales that
match existing entries in <code class="literal">pg_collation</code> will be skipped.
(But collation objects based on locales that are no longer
present in the operating system are not removed by this function.)
The <em class="parameter"><code>schema</code></em> parameter would typically
be <code class="literal">pg_catalog</code>, but that is not a requirement;
the collations could be installed into some other schema as well.
The function returns the number of new collation objects it created.
</p></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>
<a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-INDEX-TABLE" title="Table 9.87. Index Maintenance Functions">Table 9.87</a> shows the functions
available for index maintenance tasks.
These functions cannot be executed during recovery.
Use of these functions is restricted to superusers and the owner
of the given index.
</p><div class="table" id="FUNCTIONS-ADMIN-INDEX-TABLE"><p class="title"><strong>Table 9.87. 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>
<code class="literal"><code class="function">brin_summarize_new_values(<em class="parameter"><code>index</code></em> <code class="type">regclass</code>)</code></code>
</td><td><code class="type">integer</code></td><td>summarize page ranges not already summarized</td></tr><tr><td>
<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>
</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>
<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>
</td><td><code class="type">integer</code></td><td>de-summarize the page range covering the given block, if summarized</td></tr><tr><td>
<code class="literal"><code class="function">gin_clean_pending_list(<em class="parameter"><code>index</code></em> <code class="type">regclass</code>)</code></code>
</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>
<code class="function">brin_summarize_new_values</code> accepts the OID or name of a
BRIN index and inspects the index to find page ranges in the base table
that are not currently summarized by the index; for any such range
it creates a new summary index tuple by scanning the table pages.
It returns the number of new page range summaries that were inserted
into the index. <code class="function">brin_summarize_range</code> does the same, except
it only summarizes the range that covers the given block number.
</p><p>
<code class="function">gin_clean_pending_list</code> accepts the OID or name of
a GIN index and cleans up the pending list of the specified index
by moving entries in it to the main GIN data structure in bulk.
It returns the number of pages removed from the pending list.
Note that if the argument is a GIN index built with
the <code class="literal">fastupdate</code> option disabled, no cleanup happens and the
return value is 0, because the index doesn't have a pending list.
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>
for details of the pending list and <code class="literal">fastupdate</code> option.
</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>
The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-GENFILE-TABLE" title="Table 9.88. Generic File Access Functions">Table 9.88</a> provide native access to
files on the machine hosting the server. Only files within the
database cluster directory and the <code class="varname">log_directory</code> can be
accessed unless the user is granted the role
<code class="literal">pg_read_server_files</code>. Use a relative path for files in
the cluster directory, and a path matching the <code class="varname">log_directory</code>
configuration setting for log files.
</p><p>
Note that granting users the EXECUTE privilege on
<code class="function">pg_read_file()</code>, or related functions, allows them the
ability to read any file on the server which the database can read and
that those reads bypass all in-database privilege checks. This means that,
among other things, a user with this access is able to read the contents of the
<code class="literal">pg_authid</code> table where authentication information is contained,
as well as read any file in the database. Therefore, granting access to these
functions should be carefully considered.
</p><div class="table" id="FUNCTIONS-ADMIN-GENFILE-TABLE"><p class="title"><strong>Table 9.88. 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>
<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>
</td><td><code class="type">setof text</code></td><td>
List the contents of a directory. Restricted to superusers by default, but other users can be granted EXECUTE to run the function.
</td></tr><tr><td>
<code class="literal"><code class="function">pg_ls_logdir()</code></code>
</td><td><code class="type">setof record</code></td><td>
List the name, size, and last modification time of files in the log
directory. Access is granted to members of the <code class="literal">pg_monitor</code>
role and may be granted to other non-superuser roles.
</td></tr><tr><td>
<code class="literal"><code class="function">pg_ls_waldir()</code></code>
</td><td><code class="type">setof record</code></td><td>
List the name, size, and last modification time of files in the WAL
directory. Access is granted to members of the <code class="literal">pg_monitor</code>
role and may be granted to other non-superuser roles.
</td></tr><tr><td>
<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>
</td><td><code class="type">text</code></td><td>
Return the contents of a text file. Restricted to superusers by default, but other users can be granted EXECUTE to run the function.
</td></tr><tr><td>
<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>
</td><td><code class="type">bytea</code></td><td>
Return the contents of a file. Restricted to superusers by default, but other users can be granted EXECUTE to run the function.
</td></tr><tr><td>
<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>
</td><td><code class="type">record</code></td><td>
Return information about a file. Restricted to superusers by default, but other users can be granted EXECUTE to run the function.
</td></tr></tbody></table></div></div><br class="table-break" /><p>
Some of these functions take an optional <em class="parameter"><code>missing_ok</code></em> parameter,
which specifies the behavior when the file or directory does not exist.
If <code class="literal">true</code>, the function returns NULL (except
<code class="function">pg_ls_dir</code>, which returns an empty result set). If
<code class="literal">false</code>, an error is raised. The default is <code class="literal">false</code>.
</p><a id="id-1.5.8.31.11.6" class="indexterm"></a><p>
<code class="function">pg_ls_dir</code> returns the names of all files (and directories
and other special files) in the specified directory. The <em class="parameter"><code>
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
included in the result set. The default is to exclude them
(<code class="literal">false</code>), but including them can be useful when
<em class="parameter"><code>missing_ok</code></em> is <code class="literal">true</code>, to distinguish an
empty directory from an non-existent directory.
</p><a id="id-1.5.8.31.11.8" class="indexterm"></a><p>
<code class="function">pg_ls_logdir</code> returns the name, size, and last modified time
(mtime) of each file in the log directory. By default, only superusers
and members of the <code class="literal">pg_monitor</code> role can use this function.
Access may be granted to others using <code class="command">GRANT</code>.
</p><a id="id-1.5.8.31.11.10" class="indexterm"></a><p>
<code class="function">pg_ls_waldir</code> returns the name, size, and last modified time
(mtime) of each file in the write ahead log (WAL) directory. By
default only superusers and members of the <code class="literal">pg_monitor</code> role
can use this function. Access may be granted to others using
<code class="command">GRANT</code>.
</p><a id="id-1.5.8.31.11.12" class="indexterm"></a><p>
<code class="function">pg_read_file</code> returns part of a text file, starting
at the given <em class="parameter"><code>offset</code></em>, returning at most <em class="parameter"><code>length</code></em>
bytes (less if the end of file is reached first). If <em class="parameter"><code>offset</code></em>
is negative, it is relative to the end of the file.
If <em class="parameter"><code>offset</code></em> and <em class="parameter"><code>length</code></em> are omitted, the entire
file is returned. The bytes read from the file are interpreted as a string
in the server encoding; an error is thrown if they are not valid in that
encoding.
</p><a id="id-1.5.8.31.11.14" class="indexterm"></a><p>
<code class="function">pg_read_binary_file</code> is similar to
<code class="function">pg_read_file</code>, except that the result is a <code class="type">bytea</code> value;
accordingly, no encoding checks are performed.
In combination with the <code class="function">convert_from</code> function, this function
can be used to read a file in a specified encoding:
</p><pre class="programlisting">
SELECT convert_from(pg_read_binary_file('file_in_utf8.txt'), 'UTF8');
</pre><p>
</p><a id="id-1.5.8.31.11.16" class="indexterm"></a><p>
<code class="function">pg_stat_file</code> returns a record containing the file
size, last accessed time stamp, last modified time stamp,
last file status change time stamp (Unix platforms only),
file creation time stamp (Windows only), and a <code class="type">boolean</code>
indicating if it is a directory. Typical usages include:
</p><pre class="programlisting">
SELECT * FROM pg_stat_file('filename');
SELECT (pg_stat_file('filename')).modification;
</pre><p>
</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>
The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADVISORY-LOCKS-TABLE" title="Table 9.89. Advisory Lock Functions">Table 9.89</a>
manage advisory locks. For details about proper use of these functions,
see <a class="xref" href="explicit-locking.html#ADVISORY-LOCKS" title="13.3.5. Advisory Locks">Section 13.3.5</a>.
</p><div class="table" id="FUNCTIONS-ADVISORY-LOCKS-TABLE"><p class="title"><strong>Table 9.89. 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>
<code class="literal"><code class="function">pg_advisory_lock(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>
</td><td><code class="type">void</code></td><td>Obtain exclusive session level advisory lock</td></tr><tr><td>
<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>
</td><td><code class="type">void</code></td><td>Obtain exclusive session level advisory lock</td></tr><tr><td>
<code class="literal"><code class="function">pg_advisory_lock_shared(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>
</td><td><code class="type">void</code></td><td>Obtain shared session level advisory lock</td></tr><tr><td>
<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>
</td><td><code class="type">void</code></td><td>Obtain shared session level advisory lock</td></tr><tr><td>
<code class="literal"><code class="function">pg_advisory_unlock(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>
</td><td><code class="type">boolean</code></td><td>Release an exclusive session level advisory lock</td></tr><tr><td>
<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>
</td><td><code class="type">boolean</code></td><td>Release an exclusive session level advisory lock</td></tr><tr><td>
<code class="literal"><code class="function">pg_advisory_unlock_all()</code></code>
</td><td><code class="type">void</code></td><td>Release all session level advisory locks held by the current session</td></tr><tr><td>
<code class="literal"><code class="function">pg_advisory_unlock_shared(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>
</td><td><code class="type">boolean</code></td><td>Release a shared session level advisory lock</td></tr><tr><td>
<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>
</td><td><code class="type">boolean</code></td><td>Release a shared session level advisory lock</td></tr><tr><td>
<code class="literal"><code class="function">pg_advisory_xact_lock(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>
</td><td><code class="type">void</code></td><td>Obtain exclusive transaction level advisory lock</td></tr><tr><td>
<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>
</td><td><code class="type">void</code></td><td>Obtain exclusive transaction level advisory lock</td></tr><tr><td>
<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>
</td><td><code class="type">void</code></td><td>Obtain shared transaction level advisory lock</td></tr><tr><td>
<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>
</td><td><code class="type">void</code></td><td>Obtain shared transaction level advisory lock</td></tr><tr><td>
<code class="literal"><code class="function">pg_try_advisory_lock(<em class="parameter"><code>key</code></em> <code class="type">bigint</code>)</code></code>
</td><td><code class="type">boolean</code></td><td>Obtain exclusive session level advisory lock if available</td></tr><tr><td>
<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>
</td><td><code class="type">boolean</code></td><td>Obtain exclusive session level advisory lock if available</td></tr><tr><td>
<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>
</td><td><code class="type">boolean</code></td><td>Obtain shared session level advisory lock if available</td></tr><tr><td>
<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>
</td><td><code class="type">boolean</code></td><td>Obtain shared session level advisory lock if available</td></tr><tr><td>
<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>
</td><td><code class="type">boolean</code></td><td>Obtain exclusive transaction level advisory lock if available</td></tr><tr><td>
<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>
</td><td><code class="type">boolean</code></td><td>Obtain exclusive transaction level advisory lock if available</td></tr><tr><td>
<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>
</td><td><code class="type">boolean</code></td><td>Obtain shared transaction level advisory lock if available</td></tr><tr><td>
<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>
</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>
<code class="function">pg_advisory_lock</code> locks an application-defined resource,
which can be identified either by a single 64-bit key value or two
32-bit key values (note that these two key spaces do not overlap).
If another session already holds a lock on the same resource identifier,
this function will wait until the resource becomes available. The lock
is exclusive. Multiple lock requests stack, so that if the same resource
is locked three times it must then be unlocked three times to be
released for other sessions' use.
</p><a id="id-1.5.8.31.12.6" class="indexterm"></a><p>
<code class="function">pg_advisory_lock_shared</code> works the same as
<code class="function">pg_advisory_lock</code>,
except the lock can be shared with other sessions requesting shared locks.
Only would-be exclusive lockers are locked out.
</p><a id="id-1.5.8.31.12.8" class="indexterm"></a><p>
<code class="function">pg_try_advisory_lock</code> is similar to
<code class="function">pg_advisory_lock</code>, except the function will not wait for the
lock to become available. It will either obtain the lock immediately and
return <code class="literal">true</code>, or return <code class="literal">false</code> if the lock cannot be
acquired immediately.
</p><a id="id-1.5.8.31.12.10" class="indexterm"></a><p>
<code class="function">pg_try_advisory_lock_shared</code> works the same as
<code class="function">pg_try_advisory_lock</code>, except it attempts to acquire
a shared rather than an exclusive lock.
</p><a id="id-1.5.8.31.12.12" class="indexterm"></a><p>
<code class="function">pg_advisory_unlock</code> will release a previously-acquired
exclusive session level advisory lock. It
returns <code class="literal">true</code> if the lock is successfully released.
If the lock was not held, it will return <code class="literal">false</code>,
and in addition, an SQL warning will be reported by the server.
</p><a id="id-1.5.8.31.12.14" class="indexterm"></a><p>
<code class="function">pg_advisory_unlock_shared</code> works the same as
<code class="function">pg_advisory_unlock</code>,
except it releases a shared session level advisory lock.
</p><a id="id-1.5.8.31.12.16" class="indexterm"></a><p>
<code class="function">pg_advisory_unlock_all</code> will release all session level advisory
locks held by the current session. (This function is implicitly invoked
at session end, even if the client disconnects ungracefully.)
</p><a id="id-1.5.8.31.12.18" class="indexterm"></a><p>
<code class="function">pg_advisory_xact_lock</code> works the same as
<code class="function">pg_advisory_lock</code>, except the lock is automatically released
at the end of the current transaction and cannot be released explicitly.
</p><a id="id-1.5.8.31.12.20" class="indexterm"></a><p>
<code class="function">pg_advisory_xact_lock_shared</code> works the same as
<code class="function">pg_advisory_lock_shared</code>, except the lock is automatically released
at the end of the current transaction and cannot be released explicitly.
</p><a id="id-1.5.8.31.12.22" class="indexterm"></a><p>
<code class="function">pg_try_advisory_xact_lock</code> works the same as
<code class="function">pg_try_advisory_lock</code>, except the lock, if acquired,
is automatically released at the end of the current transaction and
cannot be released explicitly.
</p><a id="id-1.5.8.31.12.24" class="indexterm"></a><p>
<code class="function">pg_try_advisory_xact_lock_shared</code> works the same as
<code class="function">pg_try_advisory_lock_shared</code>, except the lock, if acquired,
is automatically released at the end of the current transaction and
cannot be released explicitly.
</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 </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>
