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postgres/doc/src/sgml/func/func-admin.sgml
Fujii Masao 38c5fbd97e doc: Improve pgoutput documentation. 
This commit updates the pgoutput documentation with the following changes:

- Specify the data type for each pgoutput option.
- Clarify the relationship between proto_version and options such as
   streaming and two_phase.
- Add a note on the use of pg_logical_slot_peek_changes and
   pg_logical_slot_get_changes with pgoutput.

Author: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Discussion: https://postgr.es/m/CAHGQGwFJTbygdhhjR_iP4Oem=Lo1xsptWWOq825uoW+hG_Lfnw@mail.gmail.com
2025-08-19 18:54:27 +09:00

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<sect1 id="functions-admin">
<title>System Administration Functions</title>
<para>
The functions described in this section are used to control and
monitor a <productname>PostgreSQL</productname> installation.
</para>
<sect2 id="functions-admin-set">
<title>Configuration Settings Functions</title>
<indexterm>
<primary>SET</primary>
</indexterm>
<indexterm>
<primary>SHOW</primary>
</indexterm>
<indexterm>
<primary>configuration</primary>
<secondary sortas="server">of the server</secondary>
<tertiary>functions</tertiary>
</indexterm>
<para>
<xref linkend="functions-admin-set-table"/> shows the functions
available to query and alter run-time configuration parameters.
</para>
<table id="functions-admin-set-table">
<title>Configuration Settings Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para>
<para>
Example(s)
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>current_setting</primary>
</indexterm>
<function>current_setting</function> ( <parameter>setting_name</parameter> <type>text</type> <optional>, <parameter>missing_ok</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the current value of the
setting <parameter>setting_name</parameter>. If there is no such
setting, <function>current_setting</function> throws an error
unless <parameter>missing_ok</parameter> is supplied and
is <literal>true</literal> (in which case NULL is returned).
This function corresponds to
the <acronym>SQL</acronym> command <xref linkend="sql-show"/>.
</para>
<para>
<literal>current_setting('datestyle')</literal>
<returnvalue>ISO, MDY</returnvalue>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>set_config</primary>
</indexterm>
<function>set_config</function> (
<parameter>setting_name</parameter> <type>text</type>,
<parameter>new_value</parameter> <type>text</type>,
<parameter>is_local</parameter> <type>boolean</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Sets the parameter <parameter>setting_name</parameter>
to <parameter>new_value</parameter>, and returns that value.
If <parameter>is_local</parameter> is <literal>true</literal>, 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 <literal>false</literal> instead. This function corresponds to
the SQL command <xref linkend="sql-set"/>.
</para>
<para>
<function>set_config</function> accepts the NULL value for
<parameter>new_value</parameter>, but as settings cannot be null, it
is interpreted as a request to reset the setting to its default value.
</para>
<para>
<literal>set_config('log_statement_stats', 'off', false)</literal>
<returnvalue>off</returnvalue>
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-admin-signal">
<title>Server Signaling Functions</title>
<indexterm>
<primary>signal</primary>
<secondary sortas="backend">backend processes</secondary>
</indexterm>
<para>
The functions shown in <xref
linkend="functions-admin-signal-table"/> 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
<command>GRANT</command>, with noted exceptions.
</para>
<para>
Each of these functions returns <literal>true</literal> if
the signal was successfully sent and <literal>false</literal>
if sending the signal failed.
</para>
<table id="functions-admin-signal-table">
<title>Server Signaling Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_cancel_backend</primary>
</indexterm>
<function>pg_cancel_backend</function> ( <parameter>pid</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
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 <literal>pg_signal_backend</literal>,
however only superusers can cancel superuser backends.
As an exception, roles with privileges of
<literal>pg_signal_autovacuum_worker</literal> are permitted to
cancel autovacuum worker processes, which are otherwise considered
superuser backends.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_log_backend_memory_contexts</primary>
</indexterm>
<function>pg_log_backend_memory_contexts</function> ( <parameter>pid</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
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
<literal>LOG</literal> message level. They will appear in
the server log based on the log configuration set
(see <xref linkend="runtime-config-logging"/> for more information),
but will not be sent to the client regardless of
<xref linkend="guc-client-min-messages"/>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_reload_conf</primary>
</indexterm>
<function>pg_reload_conf</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
Causes all processes of the <productname>PostgreSQL</productname>
server to reload their configuration files. (This is initiated by
sending a <systemitem>SIGHUP</systemitem> signal to the postmaster
process, which in turn sends <systemitem>SIGHUP</systemitem> to each
of its children.) You can use the
<link linkend="view-pg-file-settings"><structname>pg_file_settings</structname></link>,
<link linkend="view-pg-hba-file-rules"><structname>pg_hba_file_rules</structname></link> and
<link linkend="view-pg-ident-file-mappings"><structname>pg_ident_file_mappings</structname></link> views
to check the configuration files for possible errors, before reloading.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_rotate_logfile</primary>
</indexterm>
<function>pg_rotate_logfile</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
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.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_terminate_backend</primary>
</indexterm>
<function>pg_terminate_backend</function> ( <parameter>pid</parameter> <type>integer</type>, <parameter>timeout</parameter> <type>bigint</type> <literal>DEFAULT</literal> <literal>0</literal> )
<returnvalue>boolean</returnvalue>
</para>
<para>
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 <literal>pg_signal_backend</literal>,
however only superusers can terminate superuser backends.
As an exception, roles with privileges of
<literal>pg_signal_autovacuum_worker</literal> are permitted to
terminate autovacuum worker processes, which are otherwise considered
superuser backends.
</para>
<para>
If <parameter>timeout</parameter> is not specified or zero, this
function returns <literal>true</literal> whether the process actually
terminates or not, indicating only that the sending of the signal was
successful. If the <parameter>timeout</parameter> 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 <literal>true</literal>. On timeout, a warning is emitted and
<literal>false</literal> is returned.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<function>pg_cancel_backend</function> and <function>pg_terminate_backend</function>
send signals (<systemitem>SIGINT</systemitem> or <systemitem>SIGTERM</systemitem>
respectively) to backend processes identified by process ID.
The process ID of an active backend can be found from
the <structfield>pid</structfield> column of the
<structname>pg_stat_activity</structname> view, or by listing the
<command>postgres</command> processes on the server (using
<application>ps</application> on Unix or the <application>Task
Manager</application> on <productname>Windows</productname>).
The role of an active backend can be found from the
<structfield>usename</structfield> column of the
<structname>pg_stat_activity</structname> view.
</para>
<para>
<function>pg_log_backend_memory_contexts</function> can be used
to log the memory contexts of a backend process. For example:
<programlisting>
postgres=# SELECT pg_log_backend_memory_contexts(pg_backend_pid());
pg_log_backend_memory_contexts
--------------------------------
t
(1 row)
</programlisting>
One message for each memory context will be logged. For example:
<screen>
LOG: logging memory contexts of PID 10377
STATEMENT: SELECT pg_log_backend_memory_contexts(pg_backend_pid());
LOG: level: 1; TopMemoryContext: 80800 total in 6 blocks; 14432 free (5 chunks); 66368 used
LOG: level: 2; pgstat TabStatusArray lookup hash table: 8192 total in 1 blocks; 1408 free (0 chunks); 6784 used
LOG: level: 2; TopTransactionContext: 8192 total in 1 blocks; 7720 free (1 chunks); 472 used
LOG: level: 2; RowDescriptionContext: 8192 total in 1 blocks; 6880 free (0 chunks); 1312 used
LOG: level: 2; MessageContext: 16384 total in 2 blocks; 5152 free (0 chunks); 11232 used
LOG: level: 2; Operator class cache: 8192 total in 1 blocks; 512 free (0 chunks); 7680 used
LOG: level: 2; smgr relation table: 16384 total in 2 blocks; 4544 free (3 chunks); 11840 used
LOG: level: 2; TransactionAbortContext: 32768 total in 1 blocks; 32504 free (0 chunks); 264 used
...
LOG: level: 2; 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
</screen>
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.
</para>
</sect2>
<sect2 id="functions-admin-backup">
<title>Backup Control Functions</title>
<indexterm>
<primary>backup</primary>
</indexterm>
<para>
The functions shown in <xref
linkend="functions-admin-backup-table"/> assist in making on-line backups.
These functions cannot be executed during recovery (except
<function>pg_backup_start</function>,
<function>pg_backup_stop</function>,
and <function>pg_wal_lsn_diff</function>).
</para>
<para>
For details about proper usage of these functions, see
<xref linkend="continuous-archiving"/>.
</para>
<table id="functions-admin-backup-table">
<title>Backup Control Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_create_restore_point</primary>
</indexterm>
<function>pg_create_restore_point</function> ( <parameter>name</parameter> <type>text</type> )
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
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
<xref linkend="guc-recovery-target-name"/> 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.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_wal_flush_lsn</primary>
</indexterm>
<function>pg_current_wal_flush_lsn</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Returns the current write-ahead log flush location (see notes below).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_wal_insert_lsn</primary>
</indexterm>
<function>pg_current_wal_insert_lsn</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Returns the current write-ahead log insert location (see notes below).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_current_wal_lsn</primary>
</indexterm>
<function>pg_current_wal_lsn</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Returns the current write-ahead log write location (see notes below).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_backup_start</primary>
</indexterm>
<function>pg_backup_start</function> (
<parameter>label</parameter> <type>text</type>
<optional>, <parameter>fast</parameter> <type>boolean</type>
</optional> )
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
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 <literal>true</literal>,
it specifies executing <function>pg_backup_start</function> as quickly
as possible. This forces a fast checkpoint which will cause a
spike in I/O operations, slowing any concurrently executing queries.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_backup_stop</primary>
</indexterm>
<function>pg_backup_stop</function> (
<optional><parameter>wait_for_archive</parameter> <type>boolean</type>
</optional> )
<returnvalue>record</returnvalue>
( <parameter>lsn</parameter> <type>pg_lsn</type>,
<parameter>labelfile</parameter> <type>text</type>,
<parameter>spcmapfile</parameter> <type>text</type> )
</para>
<para>
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).
</para>
<para>
There is an optional parameter of type <type>boolean</type>.
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, <function>pg_backup_stop</function> will wait for
WAL to be archived when archiving is enabled. (On a standby, this
means that it will wait only when <varname>archive_mode</varname> =
<literal>always</literal>. If write activity on the primary is low,
it may be useful to run <function>pg_switch_wal</function> on the
primary in order to trigger an immediate segment switch.)
</para>
<para>
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 <function>pg_backup_start</function>, 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.
</para>
<para>
The result of the function is a single record.
The <parameter>lsn</parameter> 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.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_switch_wal</primary>
</indexterm>
<function>pg_switch_wal</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
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, <function>pg_switch_wal</function> does nothing and
returns the start location of the write-ahead log file currently in
use.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_walfile_name</primary>
</indexterm>
<function>pg_walfile_name</function> ( <parameter>lsn</parameter> <type>pg_lsn</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Converts a write-ahead log location to the name of the WAL file
holding that location.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_walfile_name_offset</primary>
</indexterm>
<function>pg_walfile_name_offset</function> ( <parameter>lsn</parameter> <type>pg_lsn</type> )
<returnvalue>record</returnvalue>
( <parameter>file_name</parameter> <type>text</type>,
<parameter>file_offset</parameter> <type>integer</type> )
</para>
<para>
Converts a write-ahead log location to a WAL file name and byte offset
within that file.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_split_walfile_name</primary>
</indexterm>
<function>pg_split_walfile_name</function> ( <parameter>file_name</parameter> <type>text</type> )
<returnvalue>record</returnvalue>
( <parameter>segment_number</parameter> <type>numeric</type>,
<parameter>timeline_id</parameter> <type>bigint</type> )
</para>
<para>
Extracts the sequence number and timeline ID from a WAL file
name.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_wal_lsn_diff</primary>
</indexterm>
<function>pg_wal_lsn_diff</function> ( <parameter>lsn1</parameter> <type>pg_lsn</type>, <parameter>lsn2</parameter> <type>pg_lsn</type> )
<returnvalue>numeric</returnvalue>
</para>
<para>
Calculates the difference in bytes (<parameter>lsn1</parameter> - <parameter>lsn2</parameter>) between two write-ahead log
locations. This can be used
with <structname>pg_stat_replication</structname> or some of the
functions shown in <xref linkend="functions-admin-backup-table"/> to
get the replication lag.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<function>pg_current_wal_lsn</function> displays the current write-ahead
log write location in the same format used by the above functions.
Similarly, <function>pg_current_wal_insert_lsn</function> displays the
current write-ahead log insertion location
and <function>pg_current_wal_flush_lsn</function> displays the current
write-ahead log flush location. The insertion location is
the <quote>logical</quote> 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.
</para>
<para>
You can use <function>pg_walfile_name_offset</function> to extract the
corresponding write-ahead log file name and byte offset from
a <type>pg_lsn</type> value. For example:
<programlisting>
postgres=# SELECT * FROM pg_walfile_name_offset((pg_backup_stop()).lsn);
file_name | file_offset
--------------------------+-------------
00000001000000000000000D | 4039624
(1 row)
</programlisting>
Similarly, <function>pg_walfile_name</function> extracts just the write-ahead log file name.
</para>
<para>
<function>pg_split_walfile_name</function> is useful to compute a
<acronym>LSN</acronym> from a file offset and WAL file name, for example:
<programlisting>
postgres=# \set file_name '000000010000000100C000AB'
postgres=# \set offset 256
postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset AS lsn
FROM pg_split_walfile_name(:'file_name') pd,
pg_show_all_settings() ps
WHERE ps.name = 'wal_segment_size';
lsn
---------------
C001/AB000100
(1 row)
</programlisting>
</para>
</sect2>
<sect2 id="functions-recovery-control">
<title>Recovery Control Functions</title>
<para>
The functions shown in <xref
linkend="functions-recovery-info-table"/> provide information
about the current status of a standby server.
These functions may be executed both during recovery and in normal running.
</para>
<table id="functions-recovery-info-table">
<title>Recovery Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_is_in_recovery</primary>
</indexterm>
<function>pg_is_in_recovery</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if recovery is still in progress.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_last_wal_receive_lsn</primary>
</indexterm>
<function>pg_last_wal_receive_lsn</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
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 <literal>NULL</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_last_wal_replay_lsn</primary>
</indexterm>
<function>pg_last_wal_replay_lsn</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
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 <literal>NULL</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_last_xact_replay_timestamp</primary>
</indexterm>
<function>pg_last_xact_replay_timestamp</function> ()
<returnvalue>timestamp with time zone</returnvalue>
</para>
<para>
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 <literal>NULL</literal>. 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 <literal>NULL</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_wal_resource_managers</primary>
</indexterm>
<function>pg_get_wal_resource_managers</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>rm_id</parameter> <type>integer</type>,
<parameter>rm_name</parameter> <type>text</type>,
<parameter>rm_builtin</parameter> <type>boolean</type> )
</para>
<para>
Returns the currently-loaded WAL resource managers in the system. The
column <parameter>rm_builtin</parameter> indicates whether it's a
built-in resource manager, or a custom resource manager loaded by an
extension.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The functions shown in <xref
linkend="functions-recovery-control-table"/> control the progress of recovery.
These functions may be executed only during recovery.
</para>
<table id="functions-recovery-control-table">
<title>Recovery Control Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_is_wal_replay_paused</primary>
</indexterm>
<function>pg_is_wal_replay_paused</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if recovery pause is requested.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_get_wal_replay_pause_state</primary>
</indexterm>
<function>pg_get_wal_replay_pause_state</function> ()
<returnvalue>text</returnvalue>
</para>
<para>
Returns recovery pause state. The return values are <literal>
not paused</literal> if pause is not requested, <literal>
pause requested</literal> if pause is requested but recovery is
not yet paused, and <literal>paused</literal> if the recovery is
actually paused.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_promote</primary>
</indexterm>
<function>pg_promote</function> ( <parameter>wait</parameter> <type>boolean</type> <literal>DEFAULT</literal> <literal>true</literal>, <parameter>wait_seconds</parameter> <type>integer</type> <literal>DEFAULT</literal> <literal>60</literal> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Promotes a standby server to primary status.
With <parameter>wait</parameter> set to <literal>true</literal> (the
default), the function waits until promotion is completed
or <parameter>wait_seconds</parameter> seconds have passed, and
returns <literal>true</literal> if promotion is successful
and <literal>false</literal> otherwise.
If <parameter>wait</parameter> is set to <literal>false</literal>, the
function returns <literal>true</literal> immediately after sending a
<literal>SIGUSR1</literal> signal to the postmaster to trigger
promotion.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_wal_replay_pause</primary>
</indexterm>
<function>pg_wal_replay_pause</function> ()
<returnvalue>void</returnvalue>
</para>
<para>
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
<function>pg_get_wal_replay_pause_state()</function>. Note that
<function>pg_is_wal_replay_paused()</function> 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.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_wal_replay_resume</primary>
</indexterm>
<function>pg_wal_replay_resume</function> ()
<returnvalue>void</returnvalue>
</para>
<para>
Restarts recovery if it was paused.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<function>pg_wal_replay_pause</function> and
<function>pg_wal_replay_resume</function> cannot be executed while
a promotion is ongoing. If a promotion is triggered while recovery
is paused, the paused state ends and promotion continues.
</para>
<para>
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.
</para>
</sect2>
<sect2 id="functions-snapshot-synchronization">
<title>Snapshot Synchronization Functions</title>
<para>
<productname>PostgreSQL</productname> allows database sessions to synchronize their
snapshots. A <firstterm>snapshot</firstterm> 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 <command>START TRANSACTION</command> commands,
so that one session sees the effects of that transaction and the other
does not.
</para>
<para>
To solve this problem, <productname>PostgreSQL</productname> allows a transaction to
<firstterm>export</firstterm> the snapshot it is using. As long as the exporting
transaction remains open, other transactions can <firstterm>import</firstterm> 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.
</para>
<para>
Snapshots are exported with the <function>pg_export_snapshot</function> function,
shown in <xref linkend="functions-snapshot-synchronization-table"/>, and
imported with the <xref linkend="sql-set-transaction"/> command.
</para>
<table id="functions-snapshot-synchronization-table">
<title>Snapshot Synchronization Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_export_snapshot</primary>
</indexterm>
<function>pg_export_snapshot</function> ()
<returnvalue>text</returnvalue>
</para>
<para>
Saves the transaction's current snapshot and returns
a <type>text</type> 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.
</para>
<para>
A transaction can export more than one snapshot, if needed. Note that
doing so is only useful in <literal>READ COMMITTED</literal>
transactions, since in <literal>REPEATABLE READ</literal> and higher
isolation levels, transactions use the same snapshot throughout their
lifetime. Once a transaction has exported any snapshots, it cannot be
prepared with <xref linkend="sql-prepare-transaction"/>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_log_standby_snapshot</primary>
</indexterm>
<function>pg_log_standby_snapshot</function> ()
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Take a snapshot of running transactions and write it to WAL, without
having to wait for bgwriter or checkpointer to log one. This is useful
for logical decoding on standby, as logical slot creation has to wait
until such a record is replayed on the standby.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-replication">
<title>Replication Management Functions</title>
<para>
The functions shown
in <xref linkend="functions-replication-table"/> are for
controlling and interacting with replication features.
See <xref linkend="streaming-replication"/>,
<xref linkend="streaming-replication-slots"/>, and
<xref linkend="replication-origins"/>
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
<literal>GRANT</literal> command.
Use of functions for replication slots is restricted to superusers
and users having <literal>REPLICATION</literal> privilege.
</para>
<para>
Many of these functions have equivalent commands in the replication
protocol; see <xref linkend="protocol-replication"/>.
</para>
<para>
The functions described in
<xref linkend="functions-admin-backup"/>,
<xref linkend="functions-recovery-control"/>, and
<xref linkend="functions-snapshot-synchronization"/>
are also relevant for replication.
</para>
<table id="functions-replication-table">
<title>Replication Management Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_create_physical_replication_slot</primary>
</indexterm>
<function>pg_create_physical_replication_slot</function> ( <parameter>slot_name</parameter> <type>name</type> <optional>, <parameter>immediately_reserve</parameter> <type>boolean</type>, <parameter>temporary</parameter> <type>boolean</type> </optional> )
<returnvalue>record</returnvalue>
( <parameter>slot_name</parameter> <type>name</type>,
<parameter>lsn</parameter> <type>pg_lsn</type> )
</para>
<para>
Creates a new physical replication slot named
<parameter>slot_name</parameter>. The name cannot be
<literal>pg_conflict_detection</literal> as it is reserved for the
conflict detection slot. The optional second parameter,
when <literal>true</literal>, specifies that the <acronym>LSN</acronym> for this
replication slot be reserved immediately; otherwise
the <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 &mdash;
see <xref linkend="protocol-replication"/>. The optional third
parameter, <parameter>temporary</parameter>, 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 <literal>CREATE_REPLICATION_SLOT
... PHYSICAL</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_drop_replication_slot</primary>
</indexterm>
<function>pg_drop_replication_slot</function> ( <parameter>slot_name</parameter> <type>name</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Drops the physical or logical replication slot
named <parameter>slot_name</parameter>. Same as replication protocol
command <literal>DROP_REPLICATION_SLOT</literal>.
</para></entry>
</row>
<row>
<entry id="pg-create-logical-replication-slot" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_create_logical_replication_slot</primary>
</indexterm>
<function>pg_create_logical_replication_slot</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>plugin</parameter> <type>name</type> <optional>, <parameter>temporary</parameter> <type>boolean</type>, <parameter>twophase</parameter> <type>boolean</type>, <parameter>failover</parameter> <type>boolean</type> </optional> )
<returnvalue>record</returnvalue>
( <parameter>slot_name</parameter> <type>name</type>,
<parameter>lsn</parameter> <type>pg_lsn</type> )
</para>
<para>
Creates a new logical (decoding) replication slot named
<parameter>slot_name</parameter> using the output plugin
<parameter>plugin</parameter>. The name cannot be
<literal>pg_conflict_detection</literal> as it is reserved for
the conflict detection slot. The optional third
parameter, <parameter>temporary</parameter>, 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,
<parameter>twophase</parameter>, when set to true, specifies
that the decoding of prepared transactions is enabled for this
slot. The optional fifth parameter,
<parameter>failover</parameter>, when set to true,
specifies that this slot is enabled to be synced to the
standbys so that logical replication can be resumed after
failover. A call to this function has the same effect as
the replication protocol command
<literal>CREATE_REPLICATION_SLOT ... LOGICAL</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_copy_physical_replication_slot</primary>
</indexterm>
<function>pg_copy_physical_replication_slot</function> ( <parameter>src_slot_name</parameter> <type>name</type>, <parameter>dst_slot_name</parameter> <type>name</type> <optional>, <parameter>temporary</parameter> <type>boolean</type> </optional> )
<returnvalue>record</returnvalue>
( <parameter>slot_name</parameter> <type>name</type>,
<parameter>lsn</parameter> <type>pg_lsn</type> )
</para>
<para>
Copies an existing physical replication slot named <parameter>src_slot_name</parameter>
to a physical replication slot named <parameter>dst_slot_name</parameter>.
The new slot name cannot be <literal>pg_conflict_detection</literal>,
as it is reserved for the conflict detection.
The copied physical slot starts to reserve WAL from the same <acronym>LSN</acronym> as the
source slot.
<parameter>temporary</parameter> is optional. If <parameter>temporary</parameter>
is omitted, the same value as the source slot is used. Copy of an
invalidated slot is not allowed.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_copy_logical_replication_slot</primary>
</indexterm>
<function>pg_copy_logical_replication_slot</function> ( <parameter>src_slot_name</parameter> <type>name</type>, <parameter>dst_slot_name</parameter> <type>name</type> <optional>, <parameter>temporary</parameter> <type>boolean</type> <optional>, <parameter>plugin</parameter> <type>name</type> </optional></optional> )
<returnvalue>record</returnvalue>
( <parameter>slot_name</parameter> <type>name</type>,
<parameter>lsn</parameter> <type>pg_lsn</type> )
</para>
<para>
Copies an existing logical replication slot
named <parameter>src_slot_name</parameter> to a logical replication
slot named <parameter>dst_slot_name</parameter>, optionally changing
the output plugin and persistence. The new slot name cannot be
<literal>pg_conflict_detection</literal> as it is reserved for
the conflict detection. The copied logical slot starts from the same
<acronym>LSN</acronym> as the source logical slot. Both
<parameter>temporary</parameter> and <parameter>plugin</parameter> are
optional; if they are omitted, the values of the source slot are used.
The <literal>failover</literal> option of the source logical slot
is not copied and is set to <literal>false</literal> by default. This
is to avoid the risk of being unable to continue logical replication
after failover to standby where the slot is being synchronized. Copy of
an invalidated slot is not allowed.
</para></entry>
</row>
<row>
<entry id="pg-logical-slot-get-changes" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_logical_slot_get_changes</primary>
</indexterm>
<function>pg_logical_slot_get_changes</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>upto_lsn</parameter> <type>pg_lsn</type>, <parameter>upto_nchanges</parameter> <type>integer</type>, <literal>VARIADIC</literal> <parameter>options</parameter> <type>text[]</type> )
<returnvalue>setof record</returnvalue>
( <parameter>lsn</parameter> <type>pg_lsn</type>,
<parameter>xid</parameter> <type>xid</type>,
<parameter>data</parameter> <type>text</type> )
</para>
<para>
Returns changes in the slot <parameter>slot_name</parameter>, starting
from the point from which changes have been consumed last. If
<parameter>upto_lsn</parameter>
and <parameter>upto_nchanges</parameter> are NULL,
logical decoding will continue until end of WAL. If
<parameter>upto_lsn</parameter> is non-NULL, decoding will include only
those transactions which commit prior to the specified LSN. If
<parameter>upto_nchanges</parameter> 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.
If the specified slot is a logical failover slot then the function will
not return until all physical slots specified in
<link linkend="guc-synchronized-standby-slots"><varname>synchronized_standby_slots</varname></link>
have confirmed WAL receipt.
</para></entry>
</row>
<row>
<entry id="pg-logical-slot-peek-changes" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_logical_slot_peek_changes</primary>
</indexterm>
<function>pg_logical_slot_peek_changes</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>upto_lsn</parameter> <type>pg_lsn</type>, <parameter>upto_nchanges</parameter> <type>integer</type>, <literal>VARIADIC</literal> <parameter>options</parameter> <type>text[]</type> )
<returnvalue>setof record</returnvalue>
( <parameter>lsn</parameter> <type>pg_lsn</type>,
<parameter>xid</parameter> <type>xid</type>,
<parameter>data</parameter> <type>text</type> )
</para>
<para>
Behaves just like
the <function>pg_logical_slot_get_changes()</function> function,
except that changes are not consumed; that is, they will be returned
again on future calls.
</para></entry>
</row>
<row>
<entry id="pg-logical-slot-get-binary-changes" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_logical_slot_get_binary_changes</primary>
</indexterm>
<function>pg_logical_slot_get_binary_changes</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>upto_lsn</parameter> <type>pg_lsn</type>, <parameter>upto_nchanges</parameter> <type>integer</type>, <literal>VARIADIC</literal> <parameter>options</parameter> <type>text[]</type> )
<returnvalue>setof record</returnvalue>
( <parameter>lsn</parameter> <type>pg_lsn</type>,
<parameter>xid</parameter> <type>xid</type>,
<parameter>data</parameter> <type>bytea</type> )
</para>
<para>
Behaves just like
the <function>pg_logical_slot_get_changes()</function> function,
except that changes are returned as <type>bytea</type>.
</para></entry>
</row>
<row>
<entry id="pg-logical-slot-peek-binary-changes" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_logical_slot_peek_binary_changes</primary>
</indexterm>
<function>pg_logical_slot_peek_binary_changes</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>upto_lsn</parameter> <type>pg_lsn</type>, <parameter>upto_nchanges</parameter> <type>integer</type>, <literal>VARIADIC</literal> <parameter>options</parameter> <type>text[]</type> )
<returnvalue>setof record</returnvalue>
( <parameter>lsn</parameter> <type>pg_lsn</type>,
<parameter>xid</parameter> <type>xid</type>,
<parameter>data</parameter> <type>bytea</type> )
</para>
<para>
Behaves just like
the <function>pg_logical_slot_peek_changes()</function> function,
except that changes are returned as <type>bytea</type>.
</para></entry>
</row>
<row>
<entry id="pg-replication-slot-advance" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_slot_advance</primary>
</indexterm>
<function>pg_replication_slot_advance</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>upto_lsn</parameter> <type>pg_lsn</type> )
<returnvalue>record</returnvalue>
( <parameter>slot_name</parameter> <type>name</type>,
<parameter>end_lsn</parameter> <type>pg_lsn</type> )
</para>
<para>
Advances the current confirmed position of a replication slot named
<parameter>slot_name</parameter>. 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. If the specified slot is a
logical failover slot then the function will not return until all
physical slots specified in
<link linkend="guc-synchronized-standby-slots"><varname>synchronized_standby_slots</varname></link>
have confirmed WAL receipt.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-create" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_create</primary>
</indexterm>
<function>pg_replication_origin_create</function> ( <parameter>node_name</parameter> <type>text</type> )
<returnvalue>oid</returnvalue>
</para>
<para>
Creates a replication origin with the given external
name, and returns the internal ID assigned to it.
The name must be no longer than 512 bytes.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-drop" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_drop</primary>
</indexterm>
<function>pg_replication_origin_drop</function> ( <parameter>node_name</parameter> <type>text</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Deletes a previously-created replication origin, including any
associated replay progress.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_oid</primary>
</indexterm>
<function>pg_replication_origin_oid</function> ( <parameter>node_name</parameter> <type>text</type> )
<returnvalue>oid</returnvalue>
</para>
<para>
Looks up a replication origin by name and returns the internal ID. If
no such replication origin is found, <literal>NULL</literal> is
returned.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-session-setup" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_session_setup</primary>
</indexterm>
<function>pg_replication_origin_session_setup</function> ( <parameter>node_name</parameter> <type>text</type> )
<returnvalue>void</returnvalue>
</para>
<para>
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 <function>pg_replication_origin_session_reset</function> to undo.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_session_reset</primary>
</indexterm>
<function>pg_replication_origin_session_reset</function> ()
<returnvalue>void</returnvalue>
</para>
<para>
Cancels the effects
of <function>pg_replication_origin_session_setup()</function>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_session_is_setup</primary>
</indexterm>
<function>pg_replication_origin_session_is_setup</function> ()
<returnvalue>boolean</returnvalue>
</para>
<para>
Returns true if a replication origin has been selected in the
current session.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-session-progress" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_session_progress</primary>
</indexterm>
<function>pg_replication_origin_session_progress</function> ( <parameter>flush</parameter> <type>boolean</type> )
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Returns the replay location for the replication origin selected in
the current session. The parameter <parameter>flush</parameter>
determines whether the corresponding local transaction will be
guaranteed to have been flushed to disk or not.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-xact-setup" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_xact_setup</primary>
</indexterm>
<function>pg_replication_origin_xact_setup</function> ( <parameter>origin_lsn</parameter> <type>pg_lsn</type>, <parameter>origin_timestamp</parameter> <type>timestamp with time zone</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Marks the current transaction as replaying a transaction that has
committed at the given <acronym>LSN</acronym> and timestamp. Can
only be called when a replication origin has been selected
using <function>pg_replication_origin_session_setup</function>.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-xact-reset" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_xact_reset</primary>
</indexterm>
<function>pg_replication_origin_xact_reset</function> ()
<returnvalue>void</returnvalue>
</para>
<para>
Cancels the effects of
<function>pg_replication_origin_xact_setup()</function>.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-advance" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_advance</primary>
</indexterm>
<function>pg_replication_origin_advance</function> ( <parameter>node_name</parameter> <type>text</type>, <parameter>lsn</parameter> <type>pg_lsn</type> )
<returnvalue>void</returnvalue>
</para>
<para>
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.
</para></entry>
</row>
<row>
<entry id="pg-replication-origin-progress" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_replication_origin_progress</primary>
</indexterm>
<function>pg_replication_origin_progress</function> ( <parameter>node_name</parameter> <type>text</type>, <parameter>flush</parameter> <type>boolean</type> )
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Returns the replay location for the given replication origin. The
parameter <parameter>flush</parameter> determines whether the
corresponding local transaction will be guaranteed to have been
flushed to disk or not.
</para></entry>
</row>
<row>
<entry id="pg-logical-emit-message" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_logical_emit_message</primary>
</indexterm>
<function>pg_logical_emit_message</function> ( <parameter>transactional</parameter> <type>boolean</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>text</type> <optional>, <parameter>flush</parameter> <type>boolean</type> <literal>DEFAULT</literal> <literal>false</literal></optional> )
<returnvalue>pg_lsn</returnvalue>
</para>
<para role="func_signature">
<function>pg_logical_emit_message</function> ( <parameter>transactional</parameter> <type>boolean</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>bytea</type> <optional>, <parameter>flush</parameter> <type>boolean</type> <literal>DEFAULT</literal> <literal>false</literal></optional> )
<returnvalue>pg_lsn</returnvalue>
</para>
<para>
Emits a logical decoding message. This can be used to pass generic
messages to logical decoding plugins through
WAL. The <parameter>transactional</parameter> 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 <parameter>prefix</parameter> parameter is a
textual prefix that can be used by logical decoding plugins to easily
recognize messages that are interesting for them.
The <parameter>content</parameter> parameter is the content of the
message, given either in text or binary form.
The <parameter>flush</parameter> parameter (default set to
<literal>false</literal>) controls if the message is immediately
flushed to WAL or not. <parameter>flush</parameter> has no effect
with <parameter>transactional</parameter>, as the message's WAL
record is flushed along with its transaction.
</para></entry>
</row>
<row>
<entry id="pg-sync-replication-slots" role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_sync_replication_slots</primary>
</indexterm>
<function>pg_sync_replication_slots</function> ()
<returnvalue>void</returnvalue>
</para>
<para>
Synchronize the logical failover replication slots from the primary
server to the standby server. This function can only be executed on the
standby server. Temporary synced slots, if any, cannot be used for
logical decoding and must be dropped after promotion. See
<xref linkend="logicaldecoding-replication-slots-synchronization"/> for details.
Note that this function is primarily intended for testing and
debugging purposes and should be used with caution. Additionally,
this function cannot be executed if
<link linkend="guc-sync-replication-slots"><varname>
sync_replication_slots</varname></link> is enabled and the slotsync
worker is already running to perform the synchronization of slots.
</para>
<caution>
<para>
If, after executing the function,
<link linkend="guc-hot-standby-feedback">
<varname>hot_standby_feedback</varname></link> is disabled on
the standby or the physical slot configured in
<link linkend="guc-primary-slot-name">
<varname>primary_slot_name</varname></link> is
removed, then it is possible that the necessary rows of the
synchronized slot will be removed by the VACUUM process on the primary
server, resulting in the synchronized slot becoming invalidated.
</para>
</caution>
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-admin-dbobject">
<title>Database Object Management Functions</title>
<para>
The functions shown in <xref linkend="functions-admin-dbsize"/> calculate
the disk space usage of database objects, or assist in presentation
or understanding of usage results. <literal>bigint</literal> results
are measured in bytes. If an OID that does
not represent an existing object is passed to one of these
functions, <literal>NULL</literal> is returned.
</para>
<table id="functions-admin-dbsize">
<title>Database Object Size Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_column_size</primary>
</indexterm>
<function>pg_column_size</function> ( <type>"any"</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
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.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_column_compression</primary>
</indexterm>
<function>pg_column_compression</function> ( <type>"any"</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Shows the compression algorithm that was used to compress
an individual variable-length value. Returns <literal>NULL</literal>
if the value is not compressed.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_column_toast_chunk_id</primary>
</indexterm>
<function>pg_column_toast_chunk_id</function> ( <type>"any"</type> )
<returnvalue>oid</returnvalue>
</para>
<para>
Shows the <structfield>chunk_id</structfield> of an on-disk
<acronym>TOAST</acronym>ed value. Returns <literal>NULL</literal>
if the value is un-<acronym>TOAST</acronym>ed or not on-disk. See
<xref linkend="storage-toast"/> for more information about
<acronym>TOAST</acronym>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_database_size</primary>
</indexterm>
<function>pg_database_size</function> ( <type>name</type> )
<returnvalue>bigint</returnvalue>
</para>
<para role="func_signature">
<function>pg_database_size</function> ( <type>oid</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the total disk space used by the database with the specified
name or OID. To use this function, you must
have <literal>CONNECT</literal> privilege on the specified database
(which is granted by default) or have privileges of
the <literal>pg_read_all_stats</literal> role.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_indexes_size</primary>
</indexterm>
<function>pg_indexes_size</function> ( <type>regclass</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the total disk space used by indexes attached to the
specified table.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_relation_size</primary>
</indexterm>
<function>pg_relation_size</function> ( <parameter>relation</parameter> <type>regclass</type> <optional>, <parameter>fork</parameter> <type>text</type> </optional> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the disk space used by one <quote>fork</quote> of the
specified relation. (Note that for most purposes it is more
convenient to use the higher-level
functions <function>pg_total_relation_size</function>
or <function>pg_table_size</function>, 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:
<itemizedlist spacing="compact">
<listitem>
<para>
<literal>main</literal> returns the size of the main
data fork of the relation.
</para>
</listitem>
<listitem>
<para>
<literal>fsm</literal> returns the size of the Free Space Map
(see <xref linkend="storage-fsm"/>) associated with the relation.
</para>
</listitem>
<listitem>
<para>
<literal>vm</literal> returns the size of the Visibility Map
(see <xref linkend="storage-vm"/>) associated with the relation.
</para>
</listitem>
<listitem>
<para>
<literal>init</literal> returns the size of the initialization
fork, if any, associated with the relation.
</para>
</listitem>
</itemizedlist>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_size_bytes</primary>
</indexterm>
<function>pg_size_bytes</function> ( <type>text</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Converts a size in human-readable format (as returned
by <function>pg_size_pretty</function>) into bytes. Valid units are
<literal>bytes</literal>, <literal>B</literal>, <literal>kB</literal>,
<literal>MB</literal>, <literal>GB</literal>, <literal>TB</literal>,
and <literal>PB</literal>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_size_pretty</primary>
</indexterm>
<function>pg_size_pretty</function> ( <type>bigint</type> )
<returnvalue>text</returnvalue>
</para>
<para role="func_signature">
<function>pg_size_pretty</function> ( <type>numeric</type> )
<returnvalue>text</returnvalue>
</para>
<para>
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<superscript>2</superscript> = 1048576 bytes, and so on.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_table_size</primary>
</indexterm>
<function>pg_table_size</function> ( <type>regclass</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the disk space used by the specified table, excluding indexes
(but including its TOAST table if any, free space map, and visibility
map).
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_tablespace_size</primary>
</indexterm>
<function>pg_tablespace_size</function> ( <type>name</type> )
<returnvalue>bigint</returnvalue>
</para>
<para role="func_signature">
<function>pg_tablespace_size</function> ( <type>oid</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the total disk space used in the tablespace with the
specified name or OID. To use this function, you must
have <literal>CREATE</literal> privilege on the specified tablespace
or have privileges of the <literal>pg_read_all_stats</literal> role,
unless it is the default tablespace for the current database.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_total_relation_size</primary>
</indexterm>
<function>pg_total_relation_size</function> ( <type>regclass</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Computes the total disk space used by the specified table, including
all indexes and <acronym>TOAST</acronym> data. The result is
equivalent to <function>pg_table_size</function>
<literal>+</literal> <function>pg_indexes_size</function>.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The functions above that operate on tables or indexes accept a
<type>regclass</type> argument, which is simply the OID of the table or index
in the <structname>pg_class</structname> system catalog. You do not have to look up
the OID by hand, however, since the <type>regclass</type> data type's input
converter will do the work for you. See <xref linkend="datatype-oid"/>
for details.
</para>
<para>
The functions shown in <xref linkend="functions-admin-dblocation"/> assist
in identifying the specific disk files associated with database objects.
</para>
<table id="functions-admin-dblocation">
<title>Database Object Location Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_relation_filenode</primary>
</indexterm>
<function>pg_relation_filenode</function> ( <parameter>relation</parameter> <type>regclass</type> )
<returnvalue>oid</returnvalue>
</para>
<para>
Returns the <quote>filenode</quote> number currently assigned to the
specified relation. The filenode is the base component of the file
name(s) used for the relation (see
<xref linkend="storage-file-layout"/> for more information).
For most relations the result is the same as
<structname>pg_class</structname>.<structfield>relfilenode</structfield>,
but for certain system catalogs <structfield>relfilenode</structfield>
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.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_relation_filepath</primary>
</indexterm>
<function>pg_relation_filepath</function> ( <parameter>relation</parameter> <type>regclass</type> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns the entire file path name (relative to the database cluster's
data directory, <varname>PGDATA</varname>) of the relation.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_filenode_relation</primary>
</indexterm>
<function>pg_filenode_relation</function> ( <parameter>tablespace</parameter> <type>oid</type>, <parameter>filenode</parameter> <type>oid</type> )
<returnvalue>regclass</returnvalue>
</para>
<para>
Returns a relation's OID given the tablespace OID and filenode it is
stored under. This is essentially the inverse mapping of
<function>pg_relation_filepath</function>. For a relation in the
database's default tablespace, the tablespace can be specified as zero.
Returns <literal>NULL</literal> if no relation in the current database
is associated with the given values.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-admin-collation"/> lists functions used to manage
collations.
</para>
<table id="functions-admin-collation">
<title>Collation Management Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_collation_actual_version</primary>
</indexterm>
<function>pg_collation_actual_version</function> ( <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
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
<structname>pg_collation</structname>.<structfield>collversion</structfield>,
then objects depending on the collation might need to be rebuilt. See
also <xref linkend="sql-altercollation"/>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_database_collation_actual_version</primary>
</indexterm>
<function>pg_database_collation_actual_version</function> ( <type>oid</type> )
<returnvalue>text</returnvalue>
</para>
<para>
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
<structname>pg_database</structname>.<structfield>datcollversion</structfield>,
then objects depending on the collation might need to be rebuilt. See
also <xref linkend="sql-alterdatabase"/>.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_import_system_collations</primary>
</indexterm>
<function>pg_import_system_collations</function> ( <parameter>schema</parameter> <type>regnamespace</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Adds collations to the system
catalog <structname>pg_collation</structname> based on all the locales
it finds in the operating system. This is
what <command>initdb</command> uses; see
<xref linkend="collation-managing"/> 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 <structname>pg_collation</structname> 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 <parameter>schema</parameter> parameter would typically
be <literal>pg_catalog</literal>, 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.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-admin-statsmod"/> lists functions used to
manipulate statistics.
These functions cannot be executed during recovery.
<warning>
<para>
Changes made by these statistics manipulation functions are likely to be
overwritten by <link linkend="autovacuum">autovacuum</link> (or manual
<command>VACUUM</command> or <command>ANALYZE</command>) and should be
considered temporary.
</para>
</warning>
</para>
<table id="functions-admin-statsmod">
<title>Database Object Statistics Manipulation Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_restore_relation_stats</primary>
</indexterm>
<function>pg_restore_relation_stats</function> (
<literal>VARIADIC</literal> <parameter>kwargs</parameter> <type>"any"</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Updates table-level statistics. Ordinarily, these statistics are
collected automatically or updated as a part of <xref
linkend="sql-vacuum"/> or <xref linkend="sql-analyze"/>, so it's not
necessary to call this function. However, it is useful after a
restore to enable the optimizer to choose better plans if
<command>ANALYZE</command> has not been run yet.
</para>
<para>
The tracked statistics may change from version to version, so
arguments are passed as pairs of <replaceable>argname</replaceable>
and <replaceable>argvalue</replaceable> in the form:
<programlisting>
SELECT pg_restore_relation_stats(
'<replaceable>arg1name</replaceable>', '<replaceable>arg1value</replaceable>'::<replaceable>arg1type</replaceable>,
'<replaceable>arg2name</replaceable>', '<replaceable>arg2value</replaceable>'::<replaceable>arg2type</replaceable>,
'<replaceable>arg3name</replaceable>', '<replaceable>arg3value</replaceable>'::<replaceable>arg3type</replaceable>);
</programlisting>
</para>
<para>
For example, to set the <structfield>relpages</structfield> and
<structfield>reltuples</structfield> values for the table
<structname>mytable</structname>:
<programlisting>
SELECT pg_restore_relation_stats(
'schemaname', 'myschema',
'relname', 'mytable',
'relpages', 173::integer,
'reltuples', 10000::real);
</programlisting>
</para>
<para>
The arguments <literal>schemaname</literal> and
<literal>relname</literal> are required, and specify the table. Other
arguments are the names and values of statistics corresponding to
certain columns in <link
linkend="catalog-pg-class"><structname>pg_class</structname></link>.
The currently-supported relation statistics are
<literal>relpages</literal> with a value of type
<type>integer</type>, <literal>reltuples</literal> with a value of
type <type>real</type>, <literal>relallvisible</literal> with a value
of type <type>integer</type>, and <literal>relallfrozen</literal>
with a value of type <type>integer</type>.
</para>
<para>
Additionally, this function accepts argument name
<literal>version</literal> of type <type>integer</type>, which
specifies the server version from which the statistics originated.
This is anticipated to be helpful in porting statistics from older
versions of <productname>PostgreSQL</productname>.
</para>
<para>
Minor errors are reported as a <literal>WARNING</literal> and
ignored, and remaining statistics will still be restored. If all
specified statistics are successfully restored, returns
<literal>true</literal>, otherwise <literal>false</literal>.
</para>
<para>
The caller must have the <literal>MAINTAIN</literal> privilege on the
table or be the owner of the database.
</para>
</entry>
</row>
<row>
<entry role="func_table_entry">
<para role="func_signature">
<indexterm>
<primary>pg_clear_relation_stats</primary>
</indexterm>
<function>pg_clear_relation_stats</function> ( <parameter>schemaname</parameter> <type>text</type>, <parameter>relname</parameter> <type>text</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Clears table-level statistics for the given relation, as though the
table was newly created.
</para>
<para>
The caller must have the <literal>MAINTAIN</literal> privilege on the
table or be the owner of the database.
</para>
</entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_restore_attribute_stats</primary>
</indexterm>
<function>pg_restore_attribute_stats</function> (
<literal>VARIADIC</literal> <parameter>kwargs</parameter> <type>"any"</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Creates or updates column-level statistics. Ordinarily, these
statistics are collected automatically or updated as a part of <xref
linkend="sql-vacuum"/> or <xref linkend="sql-analyze"/>, so it's not
necessary to call this function. However, it is useful after a
restore to enable the optimizer to choose better plans if
<command>ANALYZE</command> has not been run yet.
</para>
<para>
The tracked statistics may change from version to version, so
arguments are passed as pairs of <replaceable>argname</replaceable>
and <replaceable>argvalue</replaceable> in the form:
<programlisting>
SELECT pg_restore_attribute_stats(
'<replaceable>arg1name</replaceable>', '<replaceable>arg1value</replaceable>'::<replaceable>arg1type</replaceable>,
'<replaceable>arg2name</replaceable>', '<replaceable>arg2value</replaceable>'::<replaceable>arg2type</replaceable>,
'<replaceable>arg3name</replaceable>', '<replaceable>arg3value</replaceable>'::<replaceable>arg3type</replaceable>);
</programlisting>
</para>
<para>
For example, to set the <structfield>avg_width</structfield> and
<structfield>null_frac</structfield> values for the attribute
<structfield>col1</structfield> of the table
<structname>mytable</structname>:
<programlisting>
SELECT pg_restore_attribute_stats(
'schemaname', 'myschema',
'relname', 'mytable',
'attname', 'col1',
'inherited', false,
'avg_width', 125::integer,
'null_frac', 0.5::real);
</programlisting>
</para>
<para>
The required arguments are <literal>schemaname</literal> and
<literal>relname</literal> with a value of type <type>text</type>
which specify the table; either <literal>attname</literal> with a
value of type <type>text</type> or <literal>attnum</literal> with a
value of type <type>smallint</type>, which specifies the column; and
<literal>inherited</literal>, which specifies whether the statistics
include values from child tables. Other arguments are the names and
values of statistics corresponding to columns in <link
linkend="view-pg-stats"><structname>pg_stats</structname></link>.
</para>
<para>
Additionally, this function accepts argument name
<literal>version</literal> of type <type>integer</type>, which
specifies the server version from which the statistics originated.
This is anticipated to be helpful in porting statistics from older
versions of <productname>PostgreSQL</productname>.
</para>
<para>
Minor errors are reported as a <literal>WARNING</literal> and
ignored, and remaining statistics will still be restored. If all
specified statistics are successfully restored, returns
<literal>true</literal>, otherwise <literal>false</literal>.
</para>
<para>
The caller must have the <literal>MAINTAIN</literal> privilege on the
table or be the owner of the database.
</para>
</entry>
</row>
<row>
<entry role="func_table_entry">
<para role="func_signature">
<indexterm>
<primary>pg_clear_attribute_stats</primary>
</indexterm>
<function>pg_clear_attribute_stats</function> (
<parameter>schemaname</parameter> <type>text</type>,
<parameter>relname</parameter> <type>text</type>,
<parameter>attname</parameter> <type>text</type>,
<parameter>inherited</parameter> <type>boolean</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Clears column-level statistics for the given relation and
attribute, as though the table was newly created.
</para>
<para>
The caller must have the <literal>MAINTAIN</literal> privilege on
the table or be the owner of the database.
</para>
</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
<xref linkend="functions-info-partition"/> lists functions that provide
information about the structure of partitioned tables.
</para>
<table id="functions-info-partition">
<title>Partitioning Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_partition_tree</primary>
</indexterm>
<function>pg_partition_tree</function> ( <type>regclass</type> )
<returnvalue>setof record</returnvalue>
( <parameter>relid</parameter> <type>regclass</type>,
<parameter>parentrelid</parameter> <type>regclass</type>,
<parameter>isleaf</parameter> <type>boolean</type>,
<parameter>level</parameter> <type>integer</type> )
</para>
<para>
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.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_partition_ancestors</primary>
</indexterm>
<function>pg_partition_ancestors</function> ( <type>regclass</type> )
<returnvalue>setof regclass</returnvalue>
</para>
<para>
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.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_partition_root</primary>
</indexterm>
<function>pg_partition_root</function> ( <type>regclass</type> )
<returnvalue>regclass</returnvalue>
</para>
<para>
Returns the top-most parent of the partition tree to which the given
relation belongs. Returns <literal>NULL</literal> if the relation
does not exist or is not a partition or partitioned table.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
For example, to check the total size of the data contained in a
partitioned table <structname>measurement</structname>, one could use the
following query:
<programlisting>
SELECT pg_size_pretty(sum(pg_relation_size(relid))) AS total_size
FROM pg_partition_tree('measurement');
</programlisting>
</para>
</sect2>
<sect2 id="functions-admin-index">
<title>Index Maintenance Functions</title>
<para>
<xref linkend="functions-admin-index-table"/> 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.
</para>
<table id="functions-admin-index-table">
<title>Index Maintenance Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>brin_summarize_new_values</primary>
</indexterm>
<function>brin_summarize_new_values</function> ( <parameter>index</parameter> <type>regclass</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
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.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>brin_summarize_range</primary>
</indexterm>
<function>brin_summarize_range</function> ( <parameter>index</parameter> <type>regclass</type>, <parameter>blockNumber</parameter> <type>bigint</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Summarizes the page range covering the given block, if not already
summarized. This is
like <function>brin_summarize_new_values</function> except that it
only processes the page range that covers the given table block number.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>brin_desummarize_range</primary>
</indexterm>
<function>brin_desummarize_range</function> ( <parameter>index</parameter> <type>regclass</type>, <parameter>blockNumber</parameter> <type>bigint</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Removes the BRIN index tuple that summarizes the page range covering
the given table block, if there is one.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>gin_clean_pending_list</primary>
</indexterm>
<function>gin_clean_pending_list</function> ( <parameter>index</parameter> <type>regclass</type> )
<returnvalue>bigint</returnvalue>
</para>
<para>
Cleans up the <quote>pending</quote> 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 <literal>fastupdate</literal> option disabled, no cleanup happens
and the result is zero, because the index doesn't have a pending list.
See <xref linkend="gin-fast-update"/> and <xref linkend="gin-tips"/>
for details about the pending list and <literal>fastupdate</literal>
option.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-admin-genfile">
<title>Generic File Access Functions</title>
<para>
The functions shown in <xref
linkend="functions-admin-genfile-table"/> provide native access to
files on the machine hosting the server. Only files within the
database cluster directory and the <varname>log_directory</varname> can be
accessed, unless the user is a superuser or is granted the role
<literal>pg_read_server_files</literal>. Use a relative path for files in
the cluster directory, and a path matching the <varname>log_directory</varname>
configuration setting for log files.
</para>
<para>
Note that granting users the EXECUTE privilege on
<function>pg_read_file()</function>, 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 <structname>pg_authid</structname> 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.
</para>
<para>
When granting privilege on these functions, note that the table entries
showing optional parameters are mostly implemented as several physical
functions with different parameter lists. Privilege must be granted
separately on each such function, if it is to be
used. <application>psql</application>'s <command>\df</command> command
can be useful to check what the actual function signatures are.
</para>
<para>
Some of these functions take an optional <parameter>missing_ok</parameter>
parameter, which specifies the behavior when the file or directory does
not exist. If <literal>true</literal>, the function
returns <literal>NULL</literal> or an empty result set, as appropriate.
If <literal>false</literal>, an error is raised. (Failure conditions
other than <quote>file not found</quote> are reported as errors in any
case.) The default is <literal>false</literal>.
</para>
<table id="functions-admin-genfile-table">
<title>Generic File Access Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_dir</primary>
</indexterm>
<function>pg_ls_dir</function> ( <parameter>dirname</parameter> <type>text</type> <optional>, <parameter>missing_ok</parameter> <type>boolean</type>, <parameter>include_dot_dirs</parameter> <type>boolean</type> </optional> )
<returnvalue>setof text</returnvalue>
</para>
<para>
Returns the names of all files (and directories and other special
files) in the specified
directory. The <parameter>include_dot_dirs</parameter> parameter
indicates whether <quote>.</quote> and <quote>..</quote> are to be
included in the result set; the default is to exclude them. Including
them can be useful when <parameter>missing_ok</parameter>
is <literal>true</literal>, to distinguish an empty directory from a
non-existent directory.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_logdir</primary>
</indexterm>
<function>pg_ls_logdir</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>name</parameter> <type>text</type>,
<parameter>size</parameter> <type>bigint</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type> )
</para>
<para>
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.
</para>
<para>
This function is restricted to superusers and roles with privileges of
the <literal>pg_monitor</literal> role by default, but other users can
be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_waldir</primary>
</indexterm>
<function>pg_ls_waldir</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>name</parameter> <type>text</type>,
<parameter>size</parameter> <type>bigint</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type> )
</para>
<para>
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.
</para>
<para>
This function is restricted to superusers and roles with privileges of
the <literal>pg_monitor</literal> role by default, but other users can
be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_logicalmapdir</primary>
</indexterm>
<function>pg_ls_logicalmapdir</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>name</parameter> <type>text</type>,
<parameter>size</parameter> <type>bigint</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type> )
</para>
<para>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's <filename>pg_logical/mappings</filename>
directory. Filenames beginning with a dot, directories, and other
special files are excluded.
</para>
<para>
This function is restricted to superusers and members of
the <literal>pg_monitor</literal> role by default, but other users can
be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_logicalsnapdir</primary>
</indexterm>
<function>pg_ls_logicalsnapdir</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>name</parameter> <type>text</type>,
<parameter>size</parameter> <type>bigint</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type> )
</para>
<para>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's <filename>pg_logical/snapshots</filename>
directory. Filenames beginning with a dot, directories, and other
special files are excluded.
</para>
<para>
This function is restricted to superusers and members of
the <literal>pg_monitor</literal> role by default, but other users can
be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_replslotdir</primary>
</indexterm>
<function>pg_ls_replslotdir</function> ( <parameter>slot_name</parameter> <type>text</type> )
<returnvalue>setof record</returnvalue>
( <parameter>name</parameter> <type>text</type>,
<parameter>size</parameter> <type>bigint</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type> )
</para>
<para>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's <filename>pg_replslot/slot_name</filename>
directory, where <parameter>slot_name</parameter> 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.
</para>
<para>
This function is restricted to superusers and members of
the <literal>pg_monitor</literal> role by default, but other users can
be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_summariesdir</primary>
</indexterm>
<function>pg_ls_summariesdir</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>name</parameter> <type>text</type>,
<parameter>size</parameter> <type>bigint</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type> )
</para>
<para>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's WAL summaries directory
(<filename>pg_wal/summaries</filename>). Filenames beginning
with a dot, directories, and other special files are excluded.
</para>
<para>
This function is restricted to superusers and members of
the <literal>pg_monitor</literal> role by default, but other users can
be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_archive_statusdir</primary>
</indexterm>
<function>pg_ls_archive_statusdir</function> ()
<returnvalue>setof record</returnvalue>
( <parameter>name</parameter> <type>text</type>,
<parameter>size</parameter> <type>bigint</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type> )
</para>
<para>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the server's WAL archive status directory
(<filename>pg_wal/archive_status</filename>). Filenames beginning
with a dot, directories, and other special files are excluded.
</para>
<para>
This function is restricted to superusers and members of
the <literal>pg_monitor</literal> role by default, but other users can
be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_ls_tmpdir</primary>
</indexterm>
<function>pg_ls_tmpdir</function> ( <optional> <parameter>tablespace</parameter> <type>oid</type> </optional> )
<returnvalue>setof record</returnvalue>
( <parameter>name</parameter> <type>text</type>,
<parameter>size</parameter> <type>bigint</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type> )
</para>
<para>
Returns the name, size, and last modification time (mtime) of each
ordinary file in the temporary file directory for the
specified <parameter>tablespace</parameter>.
If <parameter>tablespace</parameter> is not provided,
the <literal>pg_default</literal> tablespace is examined. Filenames
beginning with a dot, directories, and other special files are
excluded.
</para>
<para>
This function is restricted to superusers and members of
the <literal>pg_monitor</literal> role by default, but other users can
be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_read_file</primary>
</indexterm>
<function>pg_read_file</function> ( <parameter>filename</parameter> <type>text</type> <optional>, <parameter>offset</parameter> <type>bigint</type>, <parameter>length</parameter> <type>bigint</type> </optional> <optional>, <parameter>missing_ok</parameter> <type>boolean</type> </optional> )
<returnvalue>text</returnvalue>
</para>
<para>
Returns all or part of a text file, starting at the
given byte <parameter>offset</parameter>, returning at
most <parameter>length</parameter> bytes (less if the end of file is
reached first). If <parameter>offset</parameter> is negative, it is
relative to the end of the file. If <parameter>offset</parameter>
and <parameter>length</parameter> 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.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_read_binary_file</primary>
</indexterm>
<function>pg_read_binary_file</function> ( <parameter>filename</parameter> <type>text</type> <optional>, <parameter>offset</parameter> <type>bigint</type>, <parameter>length</parameter> <type>bigint</type> </optional> <optional>, <parameter>missing_ok</parameter> <type>boolean</type> </optional> )
<returnvalue>bytea</returnvalue>
</para>
<para>
Returns all or part of a file. This function is identical to
<function>pg_read_file</function> except that it can read arbitrary
binary data, returning the result as <type>bytea</type>
not <type>text</type>; accordingly, no encoding checks are performed.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para>
<para>
In combination with the <function>convert_from</function> function,
this function can be used to read a text file in a specified encoding
and convert to the database's encoding:
<programlisting>
SELECT convert_from(pg_read_binary_file('file_in_utf8.txt'), 'UTF8');
</programlisting>
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_stat_file</primary>
</indexterm>
<function>pg_stat_file</function> ( <parameter>filename</parameter> <type>text</type> <optional>, <parameter>missing_ok</parameter> <type>boolean</type> </optional> )
<returnvalue>record</returnvalue>
( <parameter>size</parameter> <type>bigint</type>,
<parameter>access</parameter> <type>timestamp with time zone</type>,
<parameter>modification</parameter> <type>timestamp with time zone</type>,
<parameter>change</parameter> <type>timestamp with time zone</type>,
<parameter>creation</parameter> <type>timestamp with time zone</type>,
<parameter>isdir</parameter> <type>boolean</type> )
</para>
<para>
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.
</para>
<para>
This function is restricted to superusers by default, but other users
can be granted EXECUTE to run the function.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
<sect2 id="functions-advisory-locks">
<title>Advisory Lock Functions</title>
<para>
The functions shown in <xref linkend="functions-advisory-locks-table"/>
manage advisory locks. For details about proper use of these functions,
see <xref linkend="advisory-locks"/>.
</para>
<para>
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 <literal>false</literal> 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.
</para>
<table id="functions-advisory-locks-table">
<title>Advisory Lock Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_lock</primary>
</indexterm>
<function>pg_advisory_lock</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>void</returnvalue>
</para>
<para role="func_signature">
<function>pg_advisory_lock</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Obtains an exclusive session-level advisory lock, waiting if necessary.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_lock_shared</primary>
</indexterm>
<function>pg_advisory_lock_shared</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>void</returnvalue>
</para>
<para role="func_signature">
<function>pg_advisory_lock_shared</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Obtains a shared session-level advisory lock, waiting if necessary.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_unlock</primary>
</indexterm>
<function>pg_advisory_unlock</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<function>pg_advisory_unlock</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Releases a previously-acquired exclusive session-level advisory lock.
Returns <literal>true</literal> if the lock is successfully released.
If the lock was not held, <literal>false</literal> is returned, and in
addition, an SQL warning will be reported by the server.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_unlock_all</primary>
</indexterm>
<function>pg_advisory_unlock_all</function> ()
<returnvalue>void</returnvalue>
</para>
<para>
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.)
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_unlock_shared</primary>
</indexterm>
<function>pg_advisory_unlock_shared</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<function>pg_advisory_unlock_shared</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Releases a previously-acquired shared session-level advisory lock.
Returns <literal>true</literal> if the lock is successfully released.
If the lock was not held, <literal>false</literal> is returned, and in
addition, an SQL warning will be reported by the server.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_xact_lock</primary>
</indexterm>
<function>pg_advisory_xact_lock</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>void</returnvalue>
</para>
<para role="func_signature">
<function>pg_advisory_xact_lock</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Obtains an exclusive transaction-level advisory lock, waiting if
necessary.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_advisory_xact_lock_shared</primary>
</indexterm>
<function>pg_advisory_xact_lock_shared</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>void</returnvalue>
</para>
<para role="func_signature">
<function>pg_advisory_xact_lock_shared</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>void</returnvalue>
</para>
<para>
Obtains a shared transaction-level advisory lock, waiting if
necessary.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_try_advisory_lock</primary>
</indexterm>
<function>pg_try_advisory_lock</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<function>pg_try_advisory_lock</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Obtains an exclusive session-level advisory lock if available.
This will either obtain the lock immediately and
return <literal>true</literal>, or return <literal>false</literal>
without waiting if the lock cannot be acquired immediately.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_try_advisory_lock_shared</primary>
</indexterm>
<function>pg_try_advisory_lock_shared</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<function>pg_try_advisory_lock_shared</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Obtains a shared session-level advisory lock if available.
This will either obtain the lock immediately and
return <literal>true</literal>, or return <literal>false</literal>
without waiting if the lock cannot be acquired immediately.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_try_advisory_xact_lock</primary>
</indexterm>
<function>pg_try_advisory_xact_lock</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<function>pg_try_advisory_xact_lock</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Obtains an exclusive transaction-level advisory lock if available.
This will either obtain the lock immediately and
return <literal>true</literal>, or return <literal>false</literal>
without waiting if the lock cannot be acquired immediately.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_try_advisory_xact_lock_shared</primary>
</indexterm>
<function>pg_try_advisory_xact_lock_shared</function> ( <parameter>key</parameter> <type>bigint</type> )
<returnvalue>boolean</returnvalue>
</para>
<para role="func_signature">
<function>pg_try_advisory_xact_lock_shared</function> ( <parameter>key1</parameter> <type>integer</type>, <parameter>key2</parameter> <type>integer</type> )
<returnvalue>boolean</returnvalue>
</para>
<para>
Obtains a shared transaction-level advisory lock if available.
This will either obtain the lock immediately and
return <literal>true</literal>, or return <literal>false</literal>
without waiting if the lock cannot be acquired immediately.
</para></entry>
</row>
</tbody>
</tgroup>
</table>
</sect2>
</sect1>
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