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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!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>9.27. 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="9.26. System Information Functions and Operators" /><link rel="next" href="functions-trigger.html" title="9.28. Trigger Functions" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">9.27. System Administration Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="functions-info.html" title="9.26. 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 15.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="functions-trigger.html" title="9.28. Trigger Functions">Next</a></td></tr></table><hr /></div><div class="sect1" id="FUNCTIONS-ADMIN"><div class="titlepage"><div><div><h2 class="title" style="clear: both">9.27. 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">9.27.1. Configuration Settings Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-ADMIN-SIGNAL">9.27.2. Server Signaling Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-ADMIN-BACKUP">9.27.3. Backup Control Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-RECOVERY-CONTROL">9.27.4. Recovery Control Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-SNAPSHOT-SYNCHRONIZATION">9.27.5. Snapshot Synchronization Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-REPLICATION">9.27.6. Replication Management Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-ADMIN-DBOBJECT">9.27.7. Database Object Management Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-ADMIN-INDEX">9.27.8. Index Maintenance Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-ADMIN-GENFILE">9.27.9. Generic File Access Functions</a></span></dt><dt><span class="sect2"><a href="functions-admin.html#FUNCTIONS-ADVISORY-LOCKS">9.27.10. 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">9.27.1. Configuration Settings Functions</h3></div></div></div><a id="id-1.5.8.33.3.2" class="indexterm"></a><a id="id-1.5.8.33.3.3" class="indexterm"></a><a id="id-1.5.8.33.3.4" class="indexterm"></a><p>
<a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-SET-TABLE" title="Table 9.87. Configuration Settings Functions">Table 9.87</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 9.87. Configuration Settings Functions</strong></p><div class="table-contents"><table class="table" summary="Configuration Settings Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p>
<p>
Example(s)
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.3.6.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">current_setting</code> ( <em class="parameter"><code>setting_name</code></em> <code class="type">text</code> [<span class="optional">, <em class="parameter"><code>missing_ok</code></em> <code class="type">boolean</code> </span>] )
→ <code class="returnvalue">text</code>
</p>
<p>
Returns the current value of the
setting <em class="parameter"><code>setting_name</code></em>. If there is no such
setting, <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> (in which case NULL is returned).
This function corresponds to
the <acronym class="acronym">SQL</acronym> command <a class="xref" href="sql-show.html" title="SHOW"><span class="refentrytitle">SHOW</span></a>.
</p>
<p>
<code class="literal">current_setting('datestyle')</code>
→ <code class="returnvalue">ISO, MDY</code>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.3.6.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">set_config</code> (
<em class="parameter"><code>setting_name</code></em> <code class="type">text</code>,
<em class="parameter"><code>new_value</code></em> <code class="type">text</code>,
<em class="parameter"><code>is_local</code></em> <code class="type">boolean</code> )
→ <code class="returnvalue">text</code>
</p>
<p>
Sets the parameter <em class="parameter"><code>setting_name</code></em>
to <em class="parameter"><code>new_value</code></em>, and returns that value.
If <em class="parameter"><code>is_local</code></em> is <code class="literal">true</code>, the new
value will only apply during the current transaction. If you want the
new value to apply for the rest of the current session,
use <code class="literal">false</code> instead. This function corresponds to
the SQL command <a class="xref" href="sql-set.html" title="SET"><span class="refentrytitle">SET</span></a>.
</p>
<p>
<code class="literal">set_config('log_statement_stats', 'off', false)</code>
→ <code class="returnvalue">off</code>
</p></td></tr></tbody></table></div></div><br class="table-break" /></div><div class="sect2" id="FUNCTIONS-ADMIN-SIGNAL"><div class="titlepage"><div><div><h3 class="title">9.27.2. Server Signaling Functions</h3></div></div></div><a id="id-1.5.8.33.4.2" class="indexterm"></a><p>
The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-SIGNAL-TABLE" title="Table 9.88. Server Signaling Functions">Table 9.88</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><p>
Each of these functions returns <code class="literal">true</code> if
the signal was successfully sent and <code class="literal">false</code>
if sending the signal failed.
</p><div class="table" id="FUNCTIONS-ADMIN-SIGNAL-TABLE"><p class="title"><strong>Table 9.88. Server Signaling Functions</strong></p><div class="table-contents"><table class="table" summary="Server Signaling Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.4.5.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">pg_cancel_backend</code> ( <em class="parameter"><code>pid</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p>
Cancels the current query of the session whose backend process has the
specified process ID. This is also allowed if the
calling role is a member of the role whose backend is being canceled or
the calling role has privileges of <code class="literal">pg_signal_backend</code>,
however only superusers can cancel superuser backends.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.4.5.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">pg_log_backend_memory_contexts</code> ( <em class="parameter"><code>pid</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p>
Requests to log the memory contexts of the backend with the
specified process ID. This function can send the request to
backends and auxiliary processes except logger. These memory contexts
will be logged at
<code class="literal">LOG</code> message level. They will appear in
the server log based on the log configuration set
(see <a class="xref" href="runtime-config-logging.html" title="20.8. Error Reporting and Logging">Section 20.8</a> for more information),
but will not be sent to the client regardless of
<a class="xref" href="runtime-config-client.html#GUC-CLIENT-MIN-MESSAGES">client_min_messages</a>.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.4.5.2.2.3.1.1.1" class="indexterm"></a>
<code class="function">pg_reload_conf</code> ()
→ <code class="returnvalue">boolean</code>
</p>
<p>
Causes all processes of the <span class="productname">PostgreSQL</span>
server to reload their configuration files. (This is initiated by
sending a <span class="systemitem">SIGHUP</span> signal to the postmaster
process, which in turn sends <span class="systemitem">SIGHUP</span> to each
of its children.) You can use the
<a class="link" href="view-pg-file-settings.html" title="54.7. pg_file_settings"><code class="structname">pg_file_settings</code></a>,
<a class="link" href="view-pg-hba-file-rules.html" title="54.9. pg_hba_file_rules"><code class="structname">pg_hba_file_rules</code></a> and
<a class="link" href="view-pg-hba-file-rules.html" title="54.9. pg_hba_file_rules"><code class="structname">pg_ident_file_mappings</code></a> views
to check the configuration files for possible errors, before reloading.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.4.5.2.2.4.1.1.1" class="indexterm"></a>
<code class="function">pg_rotate_logfile</code> ()
→ <code class="returnvalue">boolean</code>
</p>
<p>
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></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.4.5.2.2.5.1.1.1" class="indexterm"></a>
<code class="function">pg_terminate_backend</code> ( <em class="parameter"><code>pid</code></em> <code class="type">integer</code>, <em class="parameter"><code>timeout</code></em> <code class="type">bigint</code> <code class="literal">DEFAULT</code> <code class="literal">0</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p>
Terminates the session whose backend process has the
specified process ID. This is also allowed if the calling role
is a member of the role whose backend is being terminated or the
calling role has privileges of <code class="literal">pg_signal_backend</code>,
however only superusers can terminate superuser backends.
</p>
<p>
If <em class="parameter"><code>timeout</code></em> is not specified or zero, this
function returns <code class="literal">true</code> whether the process actually
terminates or not, indicating only that the sending of the signal was
successful. If the <em class="parameter"><code>timeout</code></em> is specified (in
milliseconds) and greater than zero, the function waits until the
process is actually terminated or until the given time has passed. If
the process is terminated, the function
returns <code class="literal">true</code>. On timeout, a warning is emitted and
<code class="literal">false</code> is returned.
</p></td></tr></tbody></table></div></div><br class="table-break" /><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_log_backend_memory_contexts</code> can be used
to log the memory contexts of a backend process. For example:
</p><pre class="programlisting">
postgres=# SELECT pg_log_backend_memory_contexts(pg_backend_pid());
pg_log_backend_memory_contexts
--------------------------------
t
(1 row)
</pre><p>
One message for each memory context will be logged. For example:
</p><pre class="screen">
LOG: logging memory contexts of PID 10377
STATEMENT: SELECT pg_log_backend_memory_contexts(pg_backend_pid());
LOG: level: 0; TopMemoryContext: 80800 total in 6 blocks; 14432 free (5 chunks); 66368 used
LOG: level: 1; pgstat TabStatusArray lookup hash table: 8192 total in 1 blocks; 1408 free (0 chunks); 6784 used
LOG: level: 1; TopTransactionContext: 8192 total in 1 blocks; 7720 free (1 chunks); 472 used
LOG: level: 1; RowDescriptionContext: 8192 total in 1 blocks; 6880 free (0 chunks); 1312 used
LOG: level: 1; MessageContext: 16384 total in 2 blocks; 5152 free (0 chunks); 11232 used
LOG: level: 1; Operator class cache: 8192 total in 1 blocks; 512 free (0 chunks); 7680 used
LOG: level: 1; smgr relation table: 16384 total in 2 blocks; 4544 free (3 chunks); 11840 used
LOG: level: 1; TransactionAbortContext: 32768 total in 1 blocks; 32504 free (0 chunks); 264 used
...
LOG: level: 1; ErrorContext: 8192 total in 1 blocks; 7928 free (3 chunks); 264 used
LOG: Grand total: 1651920 bytes in 201 blocks; 622360 free (88 chunks); 1029560 used
</pre><p>
If there are more than 100 child contexts under the same parent, the first
100 child contexts are logged, along with a summary of the remaining contexts.
Note that frequent calls to this function could incur significant overhead,
because it may generate a large number of log messages.
</p></div><div class="sect2" id="FUNCTIONS-ADMIN-BACKUP"><div class="titlepage"><div><div><h3 class="title">9.27.3. Backup Control Functions</h3></div></div></div><a id="id-1.5.8.33.5.2" class="indexterm"></a><p>
The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-BACKUP-TABLE" title="Table 9.89. Backup Control Functions">Table 9.89</a> assist in making on-line backups.
These functions cannot be executed during recovery (except
<code class="function">pg_backup_start</code>,
<code class="function">pg_backup_stop</code>,
and <code class="function">pg_wal_lsn_diff</code>).
</p><p>
For details about proper usage of these functions, see
<a class="xref" href="continuous-archiving.html" title="26.3. Continuous Archiving and Point-in-Time Recovery (PITR)">Section 26.3</a>.
</p><div class="table" id="FUNCTIONS-ADMIN-BACKUP-TABLE"><p class="title"><strong>Table 9.89. Backup Control Functions</strong></p><div class="table-contents"><table class="table" summary="Backup Control Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.5.5.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">pg_create_restore_point</code> ( <em class="parameter"><code>name</code></em> <code class="type">text</code> )
→ <code class="returnvalue">pg_lsn</code>
</p>
<p>
Creates a named marker record in the write-ahead log that can later be
used as a recovery target, and returns the corresponding write-ahead
log location. The given name can then be used with
<a class="xref" href="runtime-config-wal.html#GUC-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>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.5.5.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">pg_current_wal_flush_lsn</code> ()
→ <code class="returnvalue">pg_lsn</code>
</p>
<p>
Returns the current write-ahead log flush location (see notes below).
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.5.5.2.2.3.1.1.1" class="indexterm"></a>
<code class="function">pg_current_wal_insert_lsn</code> ()
→ <code class="returnvalue">pg_lsn</code>
</p>
<p>
Returns the current write-ahead log insert location (see notes below).
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.5.5.2.2.4.1.1.1" class="indexterm"></a>
<code class="function">pg_current_wal_lsn</code> ()
→ <code class="returnvalue">pg_lsn</code>
</p>
<p>
Returns the current write-ahead log write location (see notes below).
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.5.5.2.2.5.1.1.1" class="indexterm"></a>
<code class="function">pg_backup_start</code> (
<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>] )
→ <code class="returnvalue">pg_lsn</code>
</p>
<p>
Prepares the server to begin an on-line backup. The only required
parameter is an arbitrary user-defined label for the backup.
(Typically this would be the name under which the backup dump file
will be stored.)
If the optional second parameter is given as <code class="literal">true</code>,
it specifies executing <code class="function">pg_backup_start</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>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.5.5.2.2.6.1.1.1" class="indexterm"></a>
<code class="function">pg_backup_stop</code> (
[<span class="optional"><em class="parameter"><code>wait_for_archive</code></em> <code class="type">boolean</code>
</span>] )
→ <code class="returnvalue">record</code>
( <em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code>,
<em class="parameter"><code>labelfile</code></em> <code class="type">text</code>,
<em class="parameter"><code>spcmapfile</code></em> <code class="type">text</code> )
</p>
<p>
Finishes performing an on-line backup. The desired contents of the
backup label file and the tablespace map file are returned as part of
the result of the function and must be written to files in the
backup area. These files must not be written to the live data directory
(doing so will cause PostgreSQL to fail to restart in the event of a
crash).
</p>
<p>
There is an optional parameter of type <code class="type">boolean</code>.
If false, the function will return immediately after the backup is
completed, without waiting for WAL to be archived. This behavior is
only useful with backup software that independently monitors WAL
archiving. Otherwise, WAL required to make the backup consistent might
be missing and make the backup useless. By default or when this
parameter is true, <code class="function">pg_backup_stop</code> will wait for
WAL to be archived when archiving is enabled. (On a standby, this
means that it will wait only when <code class="varname">archive_mode</code> =
<code class="literal">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, this 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_backup_start</code>, the
starting and ending write-ahead log locations for the backup, and the
starting and ending times of the backup. 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>
The result of the function is a single record.
The <em class="parameter"><code>lsn</code></em> column holds the backup's ending
write-ahead log location (which again can be ignored). The second
column returns the contents of the backup label file, and the third
column returns the contents of the tablespace map file. These must be
stored as part of the backup and are required as part of the restore
process.
</p>
<p>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.5.5.2.2.7.1.1.1" class="indexterm"></a>
<code class="function">pg_switch_wal</code> ()
→ <code class="returnvalue">pg_lsn</code>
</p>
<p>
Forces the server to switch to a new write-ahead log file, which
allows the current file to be archived (assuming you are using
continuous archiving). The result is the ending write-ahead log
location plus 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>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.5.5.2.2.8.1.1.1" class="indexterm"></a>
<code class="function">pg_walfile_name</code> ( <em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code> )
→ <code class="returnvalue">text</code>
</p>
<p>
Converts a write-ahead log location to the name of the WAL file
holding that location.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.5.5.2.2.9.1.1.1" class="indexterm"></a>
<code class="function">pg_walfile_name_offset</code> ( <em class="parameter"><code>lsn</code></em> <code class="type">pg_lsn</code> )
→ <code class="returnvalue">record</code>
( <em class="parameter"><code>file_name</code></em> <code class="type">text</code>,
<em class="parameter"><code>file_offset</code></em> <code class="type">integer</code> )
</p>
<p>
Converts a write-ahead log location to a WAL file name and byte offset
within that file.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.5.5.2.2.10.1.1.1" class="indexterm"></a>
<code class="function">pg_wal_lsn_diff</code> ( <em class="parameter"><code>lsn1</code></em> <code class="type">pg_lsn</code>, <em class="parameter"><code>lsn2</code></em> <code class="type">pg_lsn</code> )
→ <code class="returnvalue">numeric</code>
</p>
<p>
Calculates the difference in bytes (<em class="parameter"><code>lsn1</code></em> - <em class="parameter"><code>lsn2</code></em>) between two write-ahead log
locations. This can be used
with <code class="structname">pg_stat_replication</code> or some of the
functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-BACKUP-TABLE" title="Table 9.89. Backup Control Functions">Table 9.89</a> to
get the replication lag.
</p></td></tr></tbody></table></div></div><br class="table-break" /><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 the flush location is the last
location known 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 all 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
a <code class="type">pg_lsn</code> value. For example:
</p><pre class="programlisting">
postgres=# SELECT * FROM pg_walfile_name_offset((pg_backup_stop()).lsn);
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></div><div class="sect2" id="FUNCTIONS-RECOVERY-CONTROL"><div class="titlepage"><div><div><h3 class="title">9.27.4. Recovery Control Functions</h3></div></div></div><p>
The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-RECOVERY-INFO-TABLE" title="Table 9.90. Recovery Information Functions">Table 9.90</a> provide information
about the current status of a standby server.
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 9.90. Recovery Information Functions</strong></p><div class="table-contents"><table class="table" summary="Recovery Information Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.6.3.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">pg_is_in_recovery</code> ()
→ <code class="returnvalue">boolean</code>
</p>
<p>
Returns true if recovery is still in progress.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.6.3.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">pg_last_wal_receive_lsn</code> ()
→ <code class="returnvalue">pg_lsn</code>
</p>
<p>
Returns the last write-ahead log location that has been received and
synced to disk by streaming replication. While streaming replication
is in progress this will increase monotonically. If recovery has
completed then this will remain static at the location 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 <code class="literal">NULL</code>.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.6.3.2.2.3.1.1.1" class="indexterm"></a>
<code class="function">pg_last_wal_replay_lsn</code> ()
→ <code class="returnvalue">pg_lsn</code>
</p>
<p>
Returns the last write-ahead log location that has been replayed
during recovery. If recovery is still in progress this will increase
monotonically. If recovery has completed then this will remain
static at the location of the last WAL record applied during recovery.
When the server has been started normally without recovery, the
function returns <code class="literal">NULL</code>.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.6.3.2.2.4.1.1.1" class="indexterm"></a>
<code class="function">pg_last_xact_replay_timestamp</code> ()
→ <code class="returnvalue">timestamp with time zone</code>
</p>
<p>
Returns the time stamp of the 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, the function
returns <code class="literal">NULL</code>. Otherwise, if recovery is still in
progress this will increase monotonically. If recovery has completed
then this will remain static at the time of the last transaction
applied during recovery. When the server has been started normally
without recovery, the function returns <code class="literal">NULL</code>.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.6.3.2.2.5.1.1.1" class="indexterm"></a>
<code class="function">pg_get_wal_resource_managers</code> ()
→ <code class="returnvalue">setof record</code>
( <em class="parameter"><code>rm_id</code></em> <code class="type">integer</code>,
<em class="parameter"><code>rm_name</code></em> <code class="type">text</code>,
<em class="parameter"><code>rm_builtin</code></em> <code class="type">boolean</code> )
</p>
<p>
Returns the currently-loaded WAL resource managers in the system. The
column <em class="parameter"><code>rm_builtin</code></em> indicates whether it's a
built-in resource manager, or a custom resource manager loaded by an
extension.
</p></td></tr></tbody></table></div></div><br class="table-break" /><p>
The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-RECOVERY-CONTROL-TABLE" title="Table 9.91. Recovery Control Functions">Table 9.91</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 9.91. Recovery Control Functions</strong></p><div class="table-contents"><table class="table" summary="Recovery Control Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.6.5.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">pg_is_wal_replay_paused</code> ()
→ <code class="returnvalue">boolean</code>
</p>
<p>
Returns true if recovery pause is requested.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.6.5.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">pg_get_wal_replay_pause_state</code> ()
→ <code class="returnvalue">text</code>
</p>
<p>
Returns recovery pause state. The return values are <code class="literal">
not paused</code> if pause is not requested, <code class="literal">
pause requested</code> if pause is requested but recovery is
not yet paused, and <code class="literal">paused</code> if the recovery is
actually paused.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.6.5.2.2.3.1.1.1" class="indexterm"></a>
<code class="function">pg_promote</code> ( <em class="parameter"><code>wait</code></em> <code class="type">boolean</code> <code class="literal">DEFAULT</code> <code class="literal">true</code>, <em class="parameter"><code>wait_seconds</code></em> <code class="type">integer</code> <code class="literal">DEFAULT</code> <code class="literal">60</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p>
Promotes a standby server to primary status.
With <em class="parameter"><code>wait</code></em> set to <code class="literal">true</code> (the
default), the function waits until promotion is completed
or <em class="parameter"><code>wait_seconds</code></em> seconds have passed, and
returns <code class="literal">true</code> if promotion is successful
and <code class="literal">false</code> otherwise.
If <em class="parameter"><code>wait</code></em> is set to <code class="literal">false</code>, the
function returns <code class="literal">true</code> immediately after sending a
<code class="literal">SIGUSR1</code> signal to the postmaster to trigger
promotion.
</p>
<p>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.6.5.2.2.4.1.1.1" class="indexterm"></a>
<code class="function">pg_wal_replay_pause</code> ()
→ <code class="returnvalue">void</code>
</p>
<p>
Request to pause recovery. A request doesn't mean that recovery stops
right away. If you want a guarantee that recovery is actually paused,
you need to check for the recovery pause state returned by
<code class="function">pg_get_wal_replay_pause_state()</code>. Note that
<code class="function">pg_is_wal_replay_paused()</code> returns whether a request
is made. While recovery is paused, no further database changes are applied.
If hot standby is active, 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>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.6.5.2.2.5.1.1.1" class="indexterm"></a>
<code class="function">pg_wal_replay_resume</code> ()
→ <code class="returnvalue">void</code>
</p>
<p>
Restarts recovery if it was paused.
</p>
<p>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</p></td></tr></tbody></table></div></div><br class="table-break" /><p>
<code class="function">pg_wal_replay_pause</code> and
<code class="function">pg_wal_replay_resume</code> cannot be executed while
a promotion is ongoing. If a promotion is triggered while recovery
is paused, the paused state ends and promotion continues.
</p><p>
If streaming replication is disabled, the paused state may continue
indefinitely without a problem. If streaming replication is in
progress then 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">9.27.5. Snapshot Synchronization Functions</h3></div></div></div><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 9.92. Snapshot Synchronization Functions">Table 9.92</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 9.92. Snapshot Synchronization Functions</strong></p><div class="table-contents"><table class="table" summary="Snapshot Synchronization Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.7.5.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">pg_export_snapshot</code> ()
→ <code class="returnvalue">text</code>
</p>
<p>
Saves the transaction's 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.
</p>
<p>
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></td></tr></tbody></table></div></div><br class="table-break" /></div><div class="sect2" id="FUNCTIONS-REPLICATION"><div class="titlepage"><div><div><h3 class="title">9.27.6. Replication Management Functions</h3></div></div></div><p>
The functions shown
in <a class="xref" href="functions-admin.html#FUNCTIONS-REPLICATION-TABLE" title="Table 9.93. Replication Management Functions">Table 9.93</a> are for
controlling and interacting with replication features.
See <a class="xref" href="warm-standby.html#STREAMING-REPLICATION" title="27.2.5. Streaming Replication">Section 27.2.5</a>,
<a class="xref" href="warm-standby.html#STREAMING-REPLICATION-SLOTS" title="27.2.6. Replication Slots">Section 27.2.6</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 only allowed to the
superuser by default, but may be allowed to other users by using the
<code class="literal">GRANT</code> command.
Use of functions for replication slots 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="55.4. Streaming Replication Protocol">Section 55.4</a>.
</p><p>
The functions described in
<a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-BACKUP" title="9.27.3. Backup Control Functions">Section 9.27.3</a>,
<a class="xref" href="functions-admin.html#FUNCTIONS-RECOVERY-CONTROL" title="9.27.4. Recovery Control Functions">Section 9.27.4</a>, and
<a class="xref" href="functions-admin.html#FUNCTIONS-SNAPSHOT-SYNCHRONIZATION" title="9.27.5. Snapshot Synchronization Functions">Section 9.27.5</a>
are also relevant for replication.
</p><div class="table" id="FUNCTIONS-REPLICATION-TABLE"><p class="title"><strong>Table 9.93. Replication Management Functions</strong></p><div class="table-contents"><table class="table" summary="Replication Management Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">pg_create_physical_replication_slot</code> ( <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 class="returnvalue">record</code>
( <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> )
</p>
<p>
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="55.4. Streaming Replication Protocol">Section 55.4</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 the 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>.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">pg_drop_replication_slot</code> ( <em class="parameter"><code>slot_name</code></em> <code class="type">name</code> )
→ <code class="returnvalue">void</code>
</p>
<p>
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 while connected to the same database the slot was created on.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.3.1.1.1" class="indexterm"></a>
<code class="function">pg_create_logical_replication_slot</code> ( <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>, <em class="parameter"><code>twophase</code></em> <code class="type">boolean</code> </span>] )
→ <code class="returnvalue">record</code>
( <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> )
</p>
<p>
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 the current session. Temporary slots are also
released upon any error. The optional fourth parameter,
<em class="parameter"><code>twophase</code></em>, when set to true, specifies
that the decoding of prepared transactions is enabled for this
slot. A call to this function has the same effect as the replication
protocol command <code class="literal">CREATE_REPLICATION_SLOT ... LOGICAL</code>.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.4.1.1.1" class="indexterm"></a>
<code class="function">pg_copy_physical_replication_slot</code> ( <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 class="returnvalue">record</code>
( <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> )
</p>
<p>
Copies an existing physical replication slot named <em class="parameter"><code>src_slot_name</code></em>
to a physical replication slot named <em class="parameter"><code>dst_slot_name</code></em>.
The copied physical slot starts to reserve WAL from the same <acronym class="acronym">LSN</acronym> as the
source slot.
<em class="parameter"><code>temporary</code></em> is optional. If <em class="parameter"><code>temporary</code></em>
is omitted, the same value as the source slot is used.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.5.1.1.1" class="indexterm"></a>
<code class="function">pg_copy_logical_replication_slot</code> ( <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 class="returnvalue">record</code>
( <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> )
</p>
<p>
Copies an existing logical replication slot
named <em class="parameter"><code>src_slot_name</code></em> to a logical replication
slot named <em class="parameter"><code>dst_slot_name</code></em>, optionally changing
the output plugin and persistence. The copied logical slot starts
from the same <acronym class="acronym">LSN</acronym> as the source logical slot. Both
<em class="parameter"><code>temporary</code></em> and <em class="parameter"><code>plugin</code></em> are
optional; if they are omitted, the values of the source slot are used.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.6.1.1.1" class="indexterm"></a>
<code class="function">pg_logical_slot_get_changes</code> ( <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">integer</code>, <code class="literal">VARIADIC</code> <em class="parameter"><code>options</code></em> <code class="type">text[]</code> )
→ <code class="returnvalue">setof record</code>
( <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> )
</p>
<p>
Returns changes in the slot <em class="parameter"><code>slot_name</code></em>, starting
from the point from which 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.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.7.1.1.1" class="indexterm"></a>
<code class="function">pg_logical_slot_peek_changes</code> ( <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">integer</code>, <code class="literal">VARIADIC</code> <em class="parameter"><code>options</code></em> <code class="type">text[]</code> )
→ <code class="returnvalue">setof record</code>
( <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> )
</p>
<p>
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.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.8.1.1.1" class="indexterm"></a>
<code class="function">pg_logical_slot_get_binary_changes</code> ( <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">integer</code>, <code class="literal">VARIADIC</code> <em class="parameter"><code>options</code></em> <code class="type">text[]</code> )
→ <code class="returnvalue">setof record</code>
( <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> )
</p>
<p>
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>.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.9.1.1.1" class="indexterm"></a>
<code class="function">pg_logical_slot_peek_binary_changes</code> ( <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">integer</code>, <code class="literal">VARIADIC</code> <em class="parameter"><code>options</code></em> <code class="type">text[]</code> )
→ <code class="returnvalue">setof record</code>
( <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> )
</p>
<p>
Behaves just like
the <code class="function">pg_logical_slot_peek_changes()</code> function,
except that changes are returned as <code class="type">bytea</code>.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.10.1.1.1" class="indexterm"></a>
<code class="function">pg_replication_slot_advance</code> ( <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 class="returnvalue">record</code>
( <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> )
</p>
<p>
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
the name of the slot and the actual position that it was advanced to.
The updated slot position information is written out at the next
checkpoint if any advancing is done. So in the event of a crash, the
slot may return to an earlier position.
</p></td></tr><tr><td id="PG-REPLICATION-ORIGIN-CREATE" class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.11.1.1.1" class="indexterm"></a>
<code class="function">pg_replication_origin_create</code> ( <em class="parameter"><code>node_name</code></em> <code class="type">text</code> )
→ <code class="returnvalue">oid</code>
</p>
<p>
Creates a replication origin with the given external
name, and returns the internal ID assigned to it.
</p></td></tr><tr><td id="PG-REPLICATION-ORIGIN-DROP" class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.12.1.1.1" class="indexterm"></a>
<code class="function">pg_replication_origin_drop</code> ( <em class="parameter"><code>node_name</code></em> <code class="type">text</code> )
→ <code class="returnvalue">void</code>
</p>
<p>
Deletes a previously-created replication origin, including any
associated replay progress.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.13.1.1.1" class="indexterm"></a>
<code class="function">pg_replication_origin_oid</code> ( <em class="parameter"><code>node_name</code></em> <code class="type">text</code> )
→ <code class="returnvalue">oid</code>
</p>
<p>
Looks up a replication origin by name and returns the internal ID. If
no such replication origin is found, <code class="literal">NULL</code> is
returned.
</p></td></tr><tr><td id="PG-REPLICATION-ORIGIN-SESSION-SETUP" class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.14.1.1.1" class="indexterm"></a>
<code class="function">pg_replication_origin_session_setup</code> ( <em class="parameter"><code>node_name</code></em> <code class="type">text</code> )
→ <code class="returnvalue">void</code>
</p>
<p>
Marks the current session as replaying from the given
origin, allowing replay progress to be tracked.
Can only be used if no origin is currently selected.
Use <code class="function">pg_replication_origin_session_reset</code> to undo.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.15.1.1.1" class="indexterm"></a>
<code class="function">pg_replication_origin_session_reset</code> ()
→ <code class="returnvalue">void</code>
</p>
<p>
Cancels the effects
of <code class="function">pg_replication_origin_session_setup()</code>.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.16.1.1.1" class="indexterm"></a>
<code class="function">pg_replication_origin_session_is_setup</code> ()
→ <code class="returnvalue">boolean</code>
</p>
<p>
Returns true if a replication origin has been selected in the
current session.
</p></td></tr><tr><td id="PG-REPLICATION-ORIGIN-SESSION-PROGRESS" class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.17.1.1.1" class="indexterm"></a>
<code class="function">pg_replication_origin_session_progress</code> ( <em class="parameter"><code>flush</code></em> <code class="type">boolean</code> )
→ <code class="returnvalue">pg_lsn</code>
</p>
<p>
Returns the replay location for the replication origin selected 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.
</p></td></tr><tr><td id="PG-REPLICATION-ORIGIN-XACT-SETUP" class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.18.1.1.1" class="indexterm"></a>
<code class="function">pg_replication_origin_xact_setup</code> ( <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">timestamp with time zone</code> )
→ <code class="returnvalue">void</code>
</p>
<p>
Marks 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 been selected
using <code class="function">pg_replication_origin_session_setup</code>.
</p></td></tr><tr><td id="PG-REPLICATION-ORIGIN-XACT-RESET" class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.19.1.1.1" class="indexterm"></a>
<code class="function">pg_replication_origin_xact_reset</code> ()
→ <code class="returnvalue">void</code>
</p>
<p>
Cancels the effects of
<code class="function">pg_replication_origin_xact_setup()</code>.
</p></td></tr><tr><td id="PG-REPLICATION-ORIGIN-ADVANCE" class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.20.1.1.1" class="indexterm"></a>
<code class="function">pg_replication_origin_advance</code> ( <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 class="returnvalue">void</code>
</p>
<p>
Sets replication progress for the given node to the given
location. This is primarily useful for setting up the initial
location, or setting a new location after configuration changes and
similar. Be aware that careless use of this function can lead to
inconsistently replicated data.
</p></td></tr><tr><td id="PG-REPLICATION-ORIGIN-PROGRESS" class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.21.1.1.1" class="indexterm"></a>
<code class="function">pg_replication_origin_progress</code> ( <em class="parameter"><code>node_name</code></em> <code class="type">text</code>, <em class="parameter"><code>flush</code></em> <code class="type">boolean</code> )
→ <code class="returnvalue">pg_lsn</code>
</p>
<p>
Returns 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.
</p></td></tr><tr><td id="PG-LOGICAL-EMIT-MESSAGE" class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.8.5.2.2.22.1.1.1" class="indexterm"></a>
<code class="function">pg_logical_emit_message</code> ( <em class="parameter"><code>transactional</code></em> <code class="type">boolean</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 class="returnvalue">pg_lsn</code>
</p>
<p class="func_signature">
<code class="function">pg_logical_emit_message</code> ( <em class="parameter"><code>transactional</code></em> <code class="type">boolean</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 class="returnvalue">pg_lsn</code>
</p>
<p>
Emits a logical decoding message. This can be used to pass generic
messages to logical decoding plugins through
WAL. The <em class="parameter"><code>transactional</code></em> parameter specifies if
the message should be part of the current transaction, or if it should
be written immediately and decoded as soon as the logical decoder
reads the record. The <em class="parameter"><code>prefix</code></em> parameter is a
textual prefix that can be used by logical decoding plugins to easily
recognize messages that are interesting for them.
The <em class="parameter"><code>content</code></em> parameter is the content of the
message, given either in text or binary form.
</p></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">9.27.7. 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 9.94. Database Object Size Functions">Table 9.94</a> calculate
the disk space usage of database objects, or assist in presentation
or understanding of usage results. <code class="literal">bigint</code> results
are measured in bytes. If an OID that does
not represent an existing object is passed to one of these
functions, <code class="literal">NULL</code> is returned.
</p><div class="table" id="FUNCTIONS-ADMIN-DBSIZE"><p class="title"><strong>Table 9.94. Database Object Size Functions</strong></p><div class="table-contents"><table class="table" summary="Database Object Size Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.3.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">pg_column_size</code> ( <code class="type">"any"</code> )
→ <code class="returnvalue">integer</code>
</p>
<p>
Shows the number of bytes used to store any individual data value. If
applied directly to a table column value, this reflects any
compression that was done.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.3.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">pg_column_compression</code> ( <code class="type">"any"</code> )
→ <code class="returnvalue">text</code>
</p>
<p>
Shows the compression algorithm that was used to compress
an individual variable-length value. Returns <code class="literal">NULL</code>
if the value is not compressed.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.3.2.2.3.1.1.1" class="indexterm"></a>
<code class="function">pg_database_size</code> ( <code class="type">name</code> )
→ <code class="returnvalue">bigint</code>
</p>
<p class="func_signature">
<code class="function">pg_database_size</code> ( <code class="type">oid</code> )
→ <code class="returnvalue">bigint</code>
</p>
<p>
Computes the total disk space used by the database with the specified
name or OID. To use this function, you must
have <code class="literal">CONNECT</code> privilege on the specified database
(which is granted by default) or have privileges of
the <code class="literal">pg_read_all_stats</code> role.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.3.2.2.4.1.1.1" class="indexterm"></a>
<code class="function">pg_indexes_size</code> ( <code class="type">regclass</code> )
→ <code class="returnvalue">bigint</code>
</p>
<p>
Computes the total disk space used by indexes attached to the
specified table.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.3.2.2.5.1.1.1" class="indexterm"></a>
<code class="function">pg_relation_size</code> ( <em class="parameter"><code>relation</code></em> <code class="type">regclass</code> [<span class="optional">, <em class="parameter"><code>fork</code></em> <code class="type">text</code> </span>] )
→ <code class="returnvalue">bigint</code>
</p>
<p>
Computes the disk space used by one <span class="quote">“<span class="quote">fork</span>”</span> of the
specified 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, this 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="73.3. Free Space Map">Section 73.3</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="73.4. Visibility Map">Section 73.4</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></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.3.2.2.6.1.1.1" class="indexterm"></a>
<code class="function">pg_size_bytes</code> ( <code class="type">text</code> )
→ <code class="returnvalue">bigint</code>
</p>
<p>
Converts a size in human-readable format (as returned
by <code class="function">pg_size_pretty</code>) into bytes.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.3.2.2.7.1.1.1" class="indexterm"></a>
<code class="function">pg_size_pretty</code> ( <code class="type">bigint</code> )
→ <code class="returnvalue">text</code>
</p>
<p class="func_signature">
<code class="function">pg_size_pretty</code> ( <code class="type">numeric</code> )
→ <code class="returnvalue">text</code>
</p>
<p>
Converts a size in bytes into a more easily human-readable format with
size units (bytes, kB, MB, GB, TB, or PB as appropriate). Note that the
units are 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></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.3.2.2.8.1.1.1" class="indexterm"></a>
<code class="function">pg_table_size</code> ( <code class="type">regclass</code> )
→ <code class="returnvalue">bigint</code>
</p>
<p>
Computes the disk space used by the specified table, excluding indexes
(but including its TOAST table if any, free space map, and visibility
map).
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.3.2.2.9.1.1.1" class="indexterm"></a>
<code class="function">pg_tablespace_size</code> ( <code class="type">name</code> )
→ <code class="returnvalue">bigint</code>
</p>
<p class="func_signature">
<code class="function">pg_tablespace_size</code> ( <code class="type">oid</code> )
→ <code class="returnvalue">bigint</code>
</p>
<p>
Computes the total disk space used in the tablespace with the
specified name or OID. To use this function, you must
have <code class="literal">CREATE</code> privilege on the specified tablespace
or have privileges of the <code class="literal">pg_read_all_stats</code> role,
unless it is the default tablespace for the current database.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.3.2.2.10.1.1.1" class="indexterm"></a>
<code class="function">pg_total_relation_size</code> ( <code class="type">regclass</code> )
→ <code class="returnvalue">bigint</code>
</p>
<p>
Computes the total disk space used by the specified table, including
all indexes and <acronym class="acronym">TOAST</acronym> data. The result is
equivalent to <code class="function">pg_table_size</code>
<code class="literal">+</code> <code class="function">pg_indexes_size</code>.
</p></td></tr></tbody></table></div></div><br class="table-break" /><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. See <a class="xref" href="datatype-oid.html" title="8.19. Object Identifier Types">Section 8.19</a>
for details.
</p><p>
The functions shown in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-DBLOCATION" title="Table 9.95. Database Object Location Functions">Table 9.95</a> assist
in identifying the specific disk files associated with database objects.
</p><div class="table" id="FUNCTIONS-ADMIN-DBLOCATION"><p class="title"><strong>Table 9.95. Database Object Location Functions</strong></p><div class="table-contents"><table class="table" summary="Database Object Location Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.6.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">pg_relation_filenode</code> ( <em class="parameter"><code>relation</code></em> <code class="type">regclass</code> )
→ <code class="returnvalue">oid</code>
</p>
<p>
Returns the <span class="quote">“<span class="quote">filenode</span>”</span> number currently assigned to the
specified relation. 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="73.1. Database File Layout">Section 73.1</a> for more information).
For most relations 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></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.6.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">pg_relation_filepath</code> ( <em class="parameter"><code>relation</code></em> <code class="type">regclass</code> )
→ <code class="returnvalue">text</code>
</p>
<p>
Returns the entire file path name (relative to the database cluster's
data directory, <code class="varname">PGDATA</code>) of the relation.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.6.2.2.3.1.1.1" class="indexterm"></a>
<code class="function">pg_filenode_relation</code> ( <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 class="returnvalue">regclass</code>
</p>
<p>
Returns a relation's OID given the tablespace OID and filenode it is
stored under. This is essentially the inverse mapping of
<code class="function">pg_relation_filepath</code>. For a relation in the
database's default tablespace, the tablespace can be specified as zero.
Returns <code class="literal">NULL</code> if no relation in the current database
is associated with the given values.
</p></td></tr></tbody></table></div></div><br class="table-break" /><p>
<a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-COLLATION" title="Table 9.96. Collation Management Functions">Table 9.96</a> lists functions used to manage
collations.
</p><div class="table" id="FUNCTIONS-ADMIN-COLLATION"><p class="title"><strong>Table 9.96. Collation Management Functions</strong></p><div class="table-contents"><table class="table" summary="Collation Management Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.8.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">pg_collation_actual_version</code> ( <code class="type">oid</code> )
→ <code class="returnvalue">text</code>
</p>
<p>
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="structname">pg_collation</code>.<code class="structfield">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></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.8.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">pg_database_collation_actual_version</code> ( <code class="type">oid</code> )
→ <code class="returnvalue">text</code>
</p>
<p>
Returns the actual version of the database's collation as it is currently
installed in the operating system. If this is different from the
value in
<code class="structname">pg_database</code>.<code class="structfield">datcollversion</code>,
then objects depending on the collation might need to be rebuilt. See
also <a class="xref" href="sql-alterdatabase.html" title="ALTER DATABASE"><span class="refentrytitle">ALTER DATABASE</span></a>.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.8.2.2.3.1.1.1" class="indexterm"></a>
<code class="function">pg_import_system_collations</code> ( <em class="parameter"><code>schema</code></em> <code class="type">regnamespace</code> )
→ <code class="returnvalue">integer</code>
</p>
<p>
Adds collations to the system
catalog <code class="structname">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="24.2.2. Managing Collations">Section 24.2.2</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="structname">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.
Use of this function is restricted to superusers.
</p></td></tr></tbody></table></div></div><br class="table-break" /><p>
<a class="xref" href="functions-admin.html#FUNCTIONS-INFO-PARTITION" title="Table 9.97. Partitioning Information Functions">Table 9.97</a> lists functions that provide
information about the structure of partitioned tables.
</p><div class="table" id="FUNCTIONS-INFO-PARTITION"><p class="title"><strong>Table 9.97. Partitioning Information Functions</strong></p><div class="table-contents"><table class="table" summary="Partitioning Information Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.10.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">pg_partition_tree</code> ( <code class="type">regclass</code> )
→ <code class="returnvalue">setof record</code>
( <em class="parameter"><code>relid</code></em> <code class="type">regclass</code>,
<em class="parameter"><code>parentrelid</code></em> <code class="type">regclass</code>,
<em class="parameter"><code>isleaf</code></em> <code class="type">boolean</code>,
<em class="parameter"><code>level</code></em> <code class="type">integer</code> )
</p>
<p>
Lists the tables or indexes in the partition tree of the
given partitioned table or partitioned index, with one row for each
partition. Information provided includes the OID of the partition,
the OID of its immediate parent, a boolean value telling if the
partition is a leaf, and an integer telling its level in the hierarchy.
The level value is 0 for the input table or index, 1 for its
immediate child partitions, 2 for their partitions, and so on.
Returns no rows if the relation does not exist or is not a partition
or partitioned table.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.10.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">pg_partition_ancestors</code> ( <code class="type">regclass</code> )
→ <code class="returnvalue">setof regclass</code>
</p>
<p>
Lists the ancestor relations of the given partition,
including the relation itself. Returns no rows if the relation
does not exist or is not a partition or partitioned table.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.9.10.2.2.3.1.1.1" class="indexterm"></a>
<code class="function">pg_partition_root</code> ( <code class="type">regclass</code> )
→ <code class="returnvalue">regclass</code>
</p>
<p>
Returns the top-most parent of the partition tree to which the given
relation belongs. Returns <code class="literal">NULL</code> if the relation
does not exist or is not a partition or partitioned table.
</p></td></tr></tbody></table></div></div><br class="table-break" /><p>
For example, to check the total size of the data contained in a
partitioned table <code class="structname">measurement</code>, one could use the
following query:
</p><pre class="programlisting">
SELECT pg_size_pretty(sum(pg_relation_size(relid))) AS total_size
FROM pg_partition_tree('measurement');
</pre><p>
</p></div><div class="sect2" id="FUNCTIONS-ADMIN-INDEX"><div class="titlepage"><div><div><h3 class="title">9.27.8. Index Maintenance Functions</h3></div></div></div><p>
<a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-INDEX-TABLE" title="Table 9.98. Index Maintenance Functions">Table 9.98</a> shows the functions
available for index maintenance tasks. (Note that these maintenance
tasks are normally done automatically by autovacuum; use of these
functions is only required in special cases.)
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 9.98. Index Maintenance Functions</strong></p><div class="table-contents"><table class="table" summary="Index Maintenance Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.10.3.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">brin_summarize_new_values</code> ( <em class="parameter"><code>index</code></em> <code class="type">regclass</code> )
→ <code class="returnvalue">integer</code>
</p>
<p>
Scans the specified BRIN 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 those table pages.
Returns the number of new page range summaries that were inserted
into the index.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.10.3.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">brin_summarize_range</code> ( <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 class="returnvalue">integer</code>
</p>
<p>
Summarizes the page range covering the given block, if not already
summarized. This is
like <code class="function">brin_summarize_new_values</code> except that it
only processes the page range that covers the given table block number.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.10.3.2.2.3.1.1.1" class="indexterm"></a>
<code class="function">brin_desummarize_range</code> ( <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 class="returnvalue">void</code>
</p>
<p>
Removes the BRIN index tuple that summarizes the page range covering
the given table block, if there is one.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.10.3.2.2.4.1.1.1" class="indexterm"></a>
<code class="function">gin_clean_pending_list</code> ( <em class="parameter"><code>index</code></em> <code class="type">regclass</code> )
→ <code class="returnvalue">bigint</code>
</p>
<p>
Cleans up the <span class="quote">“<span class="quote">pending</span>”</span> list of the specified GIN index
by moving entries in it, in bulk, to the main GIN data structure.
Returns the number of pages removed from the pending list.
If the argument is a GIN index built with
the <code class="literal">fastupdate</code> option disabled, no cleanup happens
and the result is zero, because the index doesn't have a pending list.
See <a class="xref" href="gin-implementation.html#GIN-FAST-UPDATE" title="70.4.1. GIN Fast Update Technique">Section 70.4.1</a> and <a class="xref" href="gin-tips.html" title="70.5. GIN Tips and Tricks">Section 70.5</a>
for details about the pending list and <code class="literal">fastupdate</code>
option.
</p></td></tr></tbody></table></div></div><br class="table-break" /></div><div class="sect2" id="FUNCTIONS-ADMIN-GENFILE"><div class="titlepage"><div><div><h3 class="title">9.27.9. 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 9.99. Generic File Access Functions">Table 9.99</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 a superuser or 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 that the database server process can
read; these functions bypass all in-database privilege checks. This means
that, for example, a user with such access is able to read the contents of
the <code class="structname">pg_authid</code> table where authentication
information is stored, as well as read any table data in the database.
Therefore, granting access to these functions should be carefully
considered.
</p><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 <code class="literal">NULL</code> or an empty result set, as appropriate.
If <code class="literal">false</code>, an error is raised. The default
is <code class="literal">false</code>.
</p><div class="table" id="FUNCTIONS-ADMIN-GENFILE-TABLE"><p class="title"><strong>Table 9.99. Generic File Access Functions</strong></p><div class="table-contents"><table class="table" summary="Generic File Access Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.11.5.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">pg_ls_dir</code> ( <em class="parameter"><code>dirname</code></em> <code class="type">text</code> [<span class="optional">, <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> </span>] )
→ <code class="returnvalue">setof text</code>
</p>
<p>
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> parameter
indicates whether <span class="quote">“<span class="quote">.</span>”</span> and <span class="quote">“<span class="quote">..</span>”</span> are to be
included in the result set; the default is to exclude them. 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 a
non-existent directory.
</p>
<p>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.11.5.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">pg_ls_logdir</code> ()
→ <code class="returnvalue">setof record</code>
( <em class="parameter"><code>name</code></em> <code class="type">text</code>,
<em class="parameter"><code>size</code></em> <code class="type">bigint</code>,
<em class="parameter"><code>modification</code></em> <code class="type">timestamp with time zone</code> )
</p>
<p>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's log directory. Filenames beginning with
a dot, directories, and other special files are excluded.
</p>
<p>
This function is restricted to superusers and roles with privileges of
the <code class="literal">pg_monitor</code> role by default, but other users can
be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.11.5.2.2.3.1.1.1" class="indexterm"></a>
<code class="function">pg_ls_waldir</code> ()
→ <code class="returnvalue">setof record</code>
( <em class="parameter"><code>name</code></em> <code class="type">text</code>,
<em class="parameter"><code>size</code></em> <code class="type">bigint</code>,
<em class="parameter"><code>modification</code></em> <code class="type">timestamp with time zone</code> )
</p>
<p>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's write-ahead log (WAL) directory.
Filenames beginning with a dot, directories, and other special files
are excluded.
</p>
<p>
This function is restricted to superusers and roles with privileges of
the <code class="literal">pg_monitor</code> role by default, but other users can
be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.11.5.2.2.4.1.1.1" class="indexterm"></a>
<code class="function">pg_ls_logicalmapdir</code> ()
→ <code class="returnvalue">setof record</code>
( <em class="parameter"><code>name</code></em> <code class="type">text</code>,
<em class="parameter"><code>size</code></em> <code class="type">bigint</code>,
<em class="parameter"><code>modification</code></em> <code class="type">timestamp with time zone</code> )
</p>
<p>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's <code class="filename">pg_logical/mappings</code>
directory. Filenames beginning with a dot, directories, and other
special files are excluded.
</p>
<p>
This function is restricted to superusers and members of
the <code class="literal">pg_monitor</code> role by default, but other users can
be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.11.5.2.2.5.1.1.1" class="indexterm"></a>
<code class="function">pg_ls_logicalsnapdir</code> ()
→ <code class="returnvalue">setof record</code>
( <em class="parameter"><code>name</code></em> <code class="type">text</code>,
<em class="parameter"><code>size</code></em> <code class="type">bigint</code>,
<em class="parameter"><code>modification</code></em> <code class="type">timestamp with time zone</code> )
</p>
<p>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's <code class="filename">pg_logical/snapshots</code>
directory. Filenames beginning with a dot, directories, and other
special files are excluded.
</p>
<p>
This function is restricted to superusers and members of
the <code class="literal">pg_monitor</code> role by default, but other users can
be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.11.5.2.2.6.1.1.1" class="indexterm"></a>
<code class="function">pg_ls_replslotdir</code> ( <em class="parameter"><code>slot_name</code></em> <code class="type">text</code> )
→ <code class="returnvalue">setof record</code>
( <em class="parameter"><code>name</code></em> <code class="type">text</code>,
<em class="parameter"><code>size</code></em> <code class="type">bigint</code>,
<em class="parameter"><code>modification</code></em> <code class="type">timestamp with time zone</code> )
</p>
<p>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's <code class="filename">pg_replslot/slot_name</code>
directory, where <em class="parameter"><code>slot_name</code></em> is the name of the
replication slot provided as input of the function. Filenames beginning
with a dot, directories, and other special files are excluded.
</p>
<p>
This function is restricted to superusers and members of
the <code class="literal">pg_monitor</code> role by default, but other users can
be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.11.5.2.2.7.1.1.1" class="indexterm"></a>
<code class="function">pg_ls_archive_statusdir</code> ()
→ <code class="returnvalue">setof record</code>
( <em class="parameter"><code>name</code></em> <code class="type">text</code>,
<em class="parameter"><code>size</code></em> <code class="type">bigint</code>,
<em class="parameter"><code>modification</code></em> <code class="type">timestamp with time zone</code> )
</p>
<p>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's WAL archive status directory
(<code class="filename">pg_wal/archive_status</code>). Filenames beginning
with a dot, directories, and other special files are excluded.
</p>
<p>
This function is restricted to superusers and members of
the <code class="literal">pg_monitor</code> role by default, but other users can
be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.11.5.2.2.8.1.1.1" class="indexterm"></a>
<code class="function">pg_ls_tmpdir</code> ( [<span class="optional"> <em class="parameter"><code>tablespace</code></em> <code class="type">oid</code> </span>] )
→ <code class="returnvalue">setof record</code>
( <em class="parameter"><code>name</code></em> <code class="type">text</code>,
<em class="parameter"><code>size</code></em> <code class="type">bigint</code>,
<em class="parameter"><code>modification</code></em> <code class="type">timestamp with time zone</code> )
</p>
<p>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the temporary file directory for the
specified <em class="parameter"><code>tablespace</code></em>.
If <em class="parameter"><code>tablespace</code></em> is not provided,
the <code class="literal">pg_default</code> tablespace is examined. Filenames
beginning with a dot, directories, and other special files are
excluded.
</p>
<p>
This function is restricted to superusers and members of
the <code class="literal">pg_monitor</code> role by default, but other users can
be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.11.5.2.2.9.1.1.1" class="indexterm"></a>
<code class="function">pg_read_file</code> ( <em class="parameter"><code>filename</code></em> <code class="type">text</code> [<span class="optional">, <em class="parameter"><code>offset</code></em> <code class="type">bigint</code>, <em class="parameter"><code>length</code></em> <code class="type">bigint</code> [<span class="optional">, <em class="parameter"><code>missing_ok</code></em> <code class="type">boolean</code> </span>]</span>] )
→ <code class="returnvalue">text</code>
</p>
<p>
Returns all or part of a text file, starting at the
given byte <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 database's encoding; an error is thrown if they are not valid in
that encoding.
</p>
<p>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.11.5.2.2.10.1.1.1" class="indexterm"></a>
<code class="function">pg_read_binary_file</code> ( <em class="parameter"><code>filename</code></em> <code class="type">text</code> [<span class="optional">, <em class="parameter"><code>offset</code></em> <code class="type">bigint</code>, <em class="parameter"><code>length</code></em> <code class="type">bigint</code> [<span class="optional">, <em class="parameter"><code>missing_ok</code></em> <code class="type">boolean</code> </span>]</span>] )
→ <code class="returnvalue">bytea</code>
</p>
<p>
Returns all or part of a file. This function is identical to
<code class="function">pg_read_file</code> except that it can read arbitrary
binary data, returning the result as <code class="type">bytea</code>
not <code class="type">text</code>; accordingly, no encoding checks are performed.
</p>
<p>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</p>
<p>
In combination with the <code class="function">convert_from</code> function,
this function can be used to read a text file in a specified encoding
and convert to the database's encoding:
</p><pre class="programlisting">
SELECT convert_from(pg_read_binary_file('file_in_utf8.txt'), 'UTF8');
</pre><p>
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.11.5.2.2.11.1.1.1" class="indexterm"></a>
<code class="function">pg_stat_file</code> ( <em class="parameter"><code>filename</code></em> <code class="type">text</code> [<span class="optional">, <em class="parameter"><code>missing_ok</code></em> <code class="type">boolean</code> </span>] )
→ <code class="returnvalue">record</code>
( <em class="parameter"><code>size</code></em> <code class="type">bigint</code>,
<em class="parameter"><code>access</code></em> <code class="type">timestamp with time zone</code>,
<em class="parameter"><code>modification</code></em> <code class="type">timestamp with time zone</code>,
<em class="parameter"><code>change</code></em> <code class="type">timestamp with time zone</code>,
<em class="parameter"><code>creation</code></em> <code class="type">timestamp with time zone</code>,
<em class="parameter"><code>isdir</code></em> <code class="type">boolean</code> )
</p>
<p>
Returns a record containing the file's size, last access time stamp,
last modification time stamp, last file status change time stamp (Unix
platforms only), file creation time stamp (Windows only), and a flag
indicating if it is a directory.
</p>
<p>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</p></td></tr></tbody></table></div></div><br class="table-break" /></div><div class="sect2" id="FUNCTIONS-ADVISORY-LOCKS"><div class="titlepage"><div><div><h3 class="title">9.27.10. 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 9.100. Advisory Lock Functions">Table 9.100</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><p>
All these functions are intended to be used to lock application-defined
resources, 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 conflicting lock on the same resource
identifier, the functions will either wait until the resource becomes
available, or return a <code class="literal">false</code> result, as appropriate for
the function.
Locks can be either shared or exclusive: a shared lock does not conflict
with other shared locks on the same resource, only with exclusive locks.
Locks can be taken at session level (so that they are held until released
or the session ends) or at transaction level (so that they are held until
the current transaction ends; there is no provision for manual release).
Multiple session-level lock requests stack, so that if the same resource
identifier is locked three times there must then be three unlock requests
to release the resource in advance of session end.
</p><div class="table" id="FUNCTIONS-ADVISORY-LOCKS-TABLE"><p class="title"><strong>Table 9.100. Advisory Lock Functions</strong></p><div class="table-contents"><table class="table" summary="Advisory Lock Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
Function
</p>
<p>
Description
</p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.12.4.2.2.1.1.1.1" class="indexterm"></a>
<code class="function">pg_advisory_lock</code> ( <em class="parameter"><code>key</code></em> <code class="type">bigint</code> )
→ <code class="returnvalue">void</code>
</p>
<p class="func_signature">
<code class="function">pg_advisory_lock</code> ( <em class="parameter"><code>key1</code></em> <code class="type">integer</code>, <em class="parameter"><code>key2</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">void</code>
</p>
<p>
Obtains an exclusive session-level advisory lock, waiting if necessary.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.12.4.2.2.2.1.1.1" class="indexterm"></a>
<code class="function">pg_advisory_lock_shared</code> ( <em class="parameter"><code>key</code></em> <code class="type">bigint</code> )
→ <code class="returnvalue">void</code>
</p>
<p class="func_signature">
<code class="function">pg_advisory_lock_shared</code> ( <em class="parameter"><code>key1</code></em> <code class="type">integer</code>, <em class="parameter"><code>key2</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">void</code>
</p>
<p>
Obtains a shared session-level advisory lock, waiting if necessary.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.12.4.2.2.3.1.1.1" class="indexterm"></a>
<code class="function">pg_advisory_unlock</code> ( <em class="parameter"><code>key</code></em> <code class="type">bigint</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="function">pg_advisory_unlock</code> ( <em class="parameter"><code>key1</code></em> <code class="type">integer</code>, <em class="parameter"><code>key2</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p>
Releases a previously-acquired exclusive session-level advisory lock.
Returns <code class="literal">true</code> if the lock is successfully released.
If the lock was not held, <code class="literal">false</code> is returned, and in
addition, an SQL warning will be reported by the server.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.12.4.2.2.4.1.1.1" class="indexterm"></a>
<code class="function">pg_advisory_unlock_all</code> ()
→ <code class="returnvalue">void</code>
</p>
<p>
Releases 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></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.12.4.2.2.5.1.1.1" class="indexterm"></a>
<code class="function">pg_advisory_unlock_shared</code> ( <em class="parameter"><code>key</code></em> <code class="type">bigint</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="function">pg_advisory_unlock_shared</code> ( <em class="parameter"><code>key1</code></em> <code class="type">integer</code>, <em class="parameter"><code>key2</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p>
Releases a previously-acquired shared session-level advisory lock.
Returns <code class="literal">true</code> if the lock is successfully released.
If the lock was not held, <code class="literal">false</code> is returned, and in
addition, an SQL warning will be reported by the server.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.12.4.2.2.6.1.1.1" class="indexterm"></a>
<code class="function">pg_advisory_xact_lock</code> ( <em class="parameter"><code>key</code></em> <code class="type">bigint</code> )
→ <code class="returnvalue">void</code>
</p>
<p class="func_signature">
<code class="function">pg_advisory_xact_lock</code> ( <em class="parameter"><code>key1</code></em> <code class="type">integer</code>, <em class="parameter"><code>key2</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">void</code>
</p>
<p>
Obtains an exclusive transaction-level advisory lock, waiting if
necessary.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.12.4.2.2.7.1.1.1" class="indexterm"></a>
<code class="function">pg_advisory_xact_lock_shared</code> ( <em class="parameter"><code>key</code></em> <code class="type">bigint</code> )
→ <code class="returnvalue">void</code>
</p>
<p class="func_signature">
<code class="function">pg_advisory_xact_lock_shared</code> ( <em class="parameter"><code>key1</code></em> <code class="type">integer</code>, <em class="parameter"><code>key2</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">void</code>
</p>
<p>
Obtains a shared transaction-level advisory lock, waiting if
necessary.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.12.4.2.2.8.1.1.1" class="indexterm"></a>
<code class="function">pg_try_advisory_lock</code> ( <em class="parameter"><code>key</code></em> <code class="type">bigint</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="function">pg_try_advisory_lock</code> ( <em class="parameter"><code>key1</code></em> <code class="type">integer</code>, <em class="parameter"><code>key2</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p>
Obtains an exclusive session-level advisory lock if available.
This will either obtain the lock immediately and
return <code class="literal">true</code>, or return <code class="literal">false</code>
without waiting if the lock cannot be acquired immediately.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.12.4.2.2.9.1.1.1" class="indexterm"></a>
<code class="function">pg_try_advisory_lock_shared</code> ( <em class="parameter"><code>key</code></em> <code class="type">bigint</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="function">pg_try_advisory_lock_shared</code> ( <em class="parameter"><code>key1</code></em> <code class="type">integer</code>, <em class="parameter"><code>key2</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p>
Obtains a shared session-level advisory lock if available.
This will either obtain the lock immediately and
return <code class="literal">true</code>, or return <code class="literal">false</code>
without waiting if the lock cannot be acquired immediately.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.12.4.2.2.10.1.1.1" class="indexterm"></a>
<code class="function">pg_try_advisory_xact_lock</code> ( <em class="parameter"><code>key</code></em> <code class="type">bigint</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="function">pg_try_advisory_xact_lock</code> ( <em class="parameter"><code>key1</code></em> <code class="type">integer</code>, <em class="parameter"><code>key2</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p>
Obtains an exclusive transaction-level advisory lock if available.
This will either obtain the lock immediately and
return <code class="literal">true</code>, or return <code class="literal">false</code>
without waiting if the lock cannot be acquired immediately.
</p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
<a id="id-1.5.8.33.12.4.2.2.11.1.1.1" class="indexterm"></a>
<code class="function">pg_try_advisory_xact_lock_shared</code> ( <em class="parameter"><code>key</code></em> <code class="type">bigint</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p class="func_signature">
<code class="function">pg_try_advisory_xact_lock_shared</code> ( <em class="parameter"><code>key1</code></em> <code class="type">integer</code>, <em class="parameter"><code>key2</code></em> <code class="type">integer</code> )
→ <code class="returnvalue">boolean</code>
</p>
<p>
Obtains a shared transaction-level advisory lock if available.
This will either obtain the lock immediately and
return <code class="literal">true</code>, or return <code class="literal">false</code>
without waiting if the lock cannot be acquired immediately.
</p></td></tr></tbody></table></div></div><br class="table-break" /></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" title="9.26. System Information Functions and Operators">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="functions-trigger.html" title="9.28. Trigger Functions">Next</a></td></tr><tr><td width="40%" align="left" valign="top">9.26. System Information Functions and Operators </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 9.28. Trigger Functions</td></tr></table></div></body></html>
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