PostgreSQL: Documentation: 18: 9.28. System Administration Functions

PostgreSQL: Documentation: 18: 9.28. System Administration Functions
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9.28. System Administration Functions
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Chapter 9. Functions and Operators
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9.28. System Administration Functions
9.28.1. Configuration Settings Functions
9.28.2. Server Signaling Functions
9.28.3. Backup Control Functions
9.28.4. Recovery Control Functions
9.28.5. Snapshot Synchronization Functions
9.28.6. Replication Management Functions
9.28.7. Database Object Management Functions
9.28.8. Index Maintenance Functions
9.28.9. Generic File Access Functions
9.28.10. Advisory Lock Functions
The functions described in this section are used to control and monitor a
PostgreSQL
installation.
9.28.1. Configuration Settings Functions
Table 9.95
shows the functions available to query and alter run-time configuration parameters.
Table 9.95. Configuration Settings Functions
Function
Description
Example(s)
current_setting
setting_name
text
missing_ok
boolean
] ) →
text
Returns the current value of the setting
setting_name
. If there is no such setting,
current_setting
throws an error unless
missing_ok
is supplied and is
true
(in which case NULL is returned). This function corresponds to the
SQL
command
SHOW
current_setting('datestyle')
ISO, MDY
set_config
setting_name
text
new_value
text
is_local
boolean
) →
text
Sets the parameter
setting_name
to
new_value
, and returns that value. If
is_local
is
true
, 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
false
instead. This function corresponds to the SQL command
SET
set_config
accepts the NULL value for
new_value
, but as settings cannot be null, it is interpreted as a request to reset the setting to its default value.
set_config('log_statement_stats', 'off', false)
off
9.28.2. Server Signaling Functions
The functions shown in
Table 9.96
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
GRANT
, with noted exceptions.
Each of these functions returns
true
if the signal was successfully sent and
false
if sending the signal failed.
Table 9.96. Server Signaling Functions
Function
Description
pg_cancel_backend
pid
integer
) →
boolean
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
pg_signal_backend
, however only superusers can cancel superuser backends. As an exception, roles with privileges of
pg_signal_autovacuum_worker
are permitted to cancel autovacuum worker processes, which are otherwise considered superuser backends.
pg_log_backend_memory_contexts
pid
integer
) →
boolean
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
LOG
message level. They will appear in the server log based on the log configuration set (see
Section 19.8
for more information), but will not be sent to the client regardless of
client_min_messages
pg_reload_conf
() →
boolean
Causes all processes of the
PostgreSQL
server to reload their configuration files. (This is initiated by sending a
SIGHUP
signal to the postmaster process, which in turn sends
SIGHUP
to each of its children.) You can use the
pg_file_settings
pg_hba_file_rules
and
pg_ident_file_mappings
views to check the configuration files for possible errors, before reloading.
pg_rotate_logfile
() →
boolean
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.
pg_terminate_backend
pid
integer
timeout
bigint
DEFAULT
) →
boolean
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
pg_signal_backend
, however only superusers can terminate superuser backends. As an exception, roles with privileges of
pg_signal_autovacuum_worker
are permitted to terminate autovacuum worker processes, which are otherwise considered superuser backends.
If
timeout
is not specified or zero, this function returns
true
whether the process actually terminates or not, indicating only that the sending of the signal was successful. If the
timeout
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
true
. On timeout, a warning is emitted and
false
is returned.
pg_cancel_backend
and
pg_terminate_backend
send signals (
SIGINT
or
SIGTERM
respectively) to backend processes identified by process ID. The process ID of an active backend can be found from the
pid
column of the
pg_stat_activity
view, or by listing the
postgres
processes on the server (using
ps
on Unix or the
Task Manager
on
Windows
). The role of an active backend can be found from the
usename
column of the
pg_stat_activity
view.
pg_log_backend_memory_contexts
can be used to log the memory contexts of a backend process. For example:
postgres=# SELECT pg_log_backend_memory_contexts(pg_backend_pid());
pg_log_backend_memory_contexts
--------------------------------
(1 row)
One message for each memory context will be logged. For example:
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
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.
9.28.3. Backup Control Functions
The functions shown in
Table 9.97
assist in making on-line backups. These functions cannot be executed during recovery (except
pg_backup_start
pg_backup_stop
, and
pg_wal_lsn_diff
).
For details about proper usage of these functions, see
Section 25.3
Table 9.97. Backup Control Functions
Function
Description
pg_create_restore_point
name
text
) →
pg_lsn
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
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.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_current_wal_flush_lsn
() →
pg_lsn
Returns the current write-ahead log flush location (see notes below).
pg_current_wal_insert_lsn
() →
pg_lsn
Returns the current write-ahead log insert location (see notes below).
pg_current_wal_lsn
() →
pg_lsn
Returns the current write-ahead log write location (see notes below).
pg_backup_start
label
text
fast
boolean
] ) →
pg_lsn
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
true
, it specifies executing
pg_backup_start
as quickly as possible. This forces an immediate checkpoint which will cause a spike in I/O operations, slowing any concurrently executing queries.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_backup_stop
( [
wait_for_archive
boolean
] ) →
record
lsn
pg_lsn
labelfile
text
spcmapfile
text
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).
There is an optional parameter of type
boolean
. 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,
pg_backup_stop
will wait for WAL to be archived when archiving is enabled. (On a standby, this means that it will wait only when
archive_mode
always
. If write activity on the primary is low, it may be useful to run
pg_switch_wal
on the primary in order to trigger an immediate segment switch.)
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
pg_backup_start
, 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.
The result of the function is a single record. The
lsn
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.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_switch_wal
() →
pg_lsn
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,
pg_switch_wal
does nothing and returns the start location of the write-ahead log file currently in use.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_walfile_name
lsn
pg_lsn
) →
text
Converts a write-ahead log location to the name of the WAL file holding that location.
pg_walfile_name_offset
lsn
pg_lsn
) →
record
file_name
text
file_offset
integer
Converts a write-ahead log location to a WAL file name and byte offset within that file.
pg_split_walfile_name
file_name
text
) →
record
segment_number
numeric
timeline_id
bigint
Extracts the sequence number and timeline ID from a WAL file name.
pg_wal_lsn_diff
lsn1
pg_lsn
lsn2
pg_lsn
) →
numeric
Calculates the difference in bytes (
lsn1
lsn2
) between two write-ahead log locations. This can be used with
pg_stat_replication
or some of the functions shown in
Table 9.97
to get the replication lag.
pg_current_wal_lsn
displays the current write-ahead log write location in the same format used by the above functions. Similarly,
pg_current_wal_insert_lsn
displays the current write-ahead log insertion location and
pg_current_wal_flush_lsn
displays the current write-ahead log flush location. The insertion location is the
logical
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.
You can use
pg_walfile_name_offset
to extract the corresponding write-ahead log file name and byte offset from a
pg_lsn
value. For example:
postgres=# SELECT * FROM pg_walfile_name_offset((pg_backup_stop()).lsn);
file_name | file_offset
--------------------------+-------------
00000001000000000000000D | 4039624
(1 row)
Similarly,
pg_walfile_name
extracts just the write-ahead log file name.
pg_split_walfile_name
is useful to compute a
LSN
from a file offset and WAL file name, for example:
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)
9.28.4. Recovery Control Functions
The functions shown in
Table 9.98
provide information about the current status of a standby server. These functions may be executed both during recovery and in normal running.
Table 9.98. Recovery Information Functions
Function
Description
pg_is_in_recovery
() →
boolean
Returns true if recovery is still in progress.
pg_last_wal_receive_lsn
() →
pg_lsn
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
NULL
pg_last_wal_replay_lsn
() →
pg_lsn
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
NULL
pg_last_xact_replay_timestamp
() →
timestamp with time zone
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
NULL
. 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
NULL
pg_get_wal_resource_managers
() →
setof record
rm_id
integer
rm_name
text
rm_builtin
boolean
Returns the currently-loaded WAL resource managers in the system. The column
rm_builtin
indicates whether it's a built-in resource manager, or a custom resource manager loaded by an extension.
The functions shown in
Table 9.99
control the progress of recovery. These functions may be executed only during recovery.
Table 9.99. Recovery Control Functions
Function
Description
pg_is_wal_replay_paused
() →
boolean
Returns true if recovery pause is requested.
pg_get_wal_replay_pause_state
() →
text
Returns recovery pause state. The return values are
not paused
if pause is not requested,
pause requested
if pause is requested but recovery is not yet paused, and
paused
if the recovery is actually paused.
pg_promote
wait
boolean
DEFAULT
true
wait_seconds
integer
DEFAULT
60
) →
boolean
Promotes a standby server to primary status. With
wait
set to
true
(the default), the function waits until promotion is completed or
wait_seconds
seconds have passed, and returns
true
if promotion is successful and
false
otherwise. If
wait
is set to
false
, the function returns
true
immediately after sending a
SIGUSR1
signal to the postmaster to trigger promotion.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_wal_replay_pause
() →
void
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
pg_get_wal_replay_pause_state()
. Note that
pg_is_wal_replay_paused()
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.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_wal_replay_resume
() →
void
Restarts recovery if it was paused.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_wal_replay_pause
and
pg_wal_replay_resume
cannot be executed while a promotion is ongoing. If a promotion is triggered while recovery is paused, the paused state ends and promotion continues.
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.
9.28.5. Snapshot Synchronization Functions
PostgreSQL
allows database sessions to synchronize their snapshots. A
snapshot
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
START TRANSACTION
commands, so that one session sees the effects of that transaction and the other does not.
To solve this problem,
PostgreSQL
allows a transaction to
export
the snapshot it is using. As long as the exporting transaction remains open, other transactions can
import
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.
Snapshots are exported with the
pg_export_snapshot
function, shown in
Table 9.100
, and imported with the
SET TRANSACTION
command.
Table 9.100. Snapshot Synchronization Functions
Function
Description
pg_export_snapshot
() →
text
Saves the transaction's current snapshot and returns a
text
string identifying the snapshot. This string must be passed (outside the database) to clients that want to import the snapshot. The snapshot is available for import only until the end of the transaction that exported it.
A transaction can export more than one snapshot, if needed. Note that doing so is only useful in
READ COMMITTED
transactions, since in
REPEATABLE READ
and higher isolation levels, transactions use the same snapshot throughout their lifetime. Once a transaction has exported any snapshots, it cannot be prepared with
PREPARE TRANSACTION
pg_log_standby_snapshot
() →
pg_lsn
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.
9.28.6. Replication Management Functions
The functions shown in
Table 9.101
are for controlling and interacting with replication features. See
Section 26.2.5
Section 26.2.6
, and
Chapter 48
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
GRANT
command. Use of functions for replication slots is restricted to superusers and users having
REPLICATION
privilege.
Many of these functions have equivalent commands in the replication protocol; see
Section 54.4
The functions described in
Section 9.28.3
Section 9.28.4
, and
Section 9.28.5
are also relevant for replication.
Table 9.101. Replication Management Functions
Function
Description
pg_create_physical_replication_slot
slot_name
name
immediately_reserve
boolean
temporary
boolean
] ) →
record
slot_name
name
lsn
pg_lsn
Creates a new physical replication slot named
slot_name
. The optional second parameter, when
true
, specifies that the
LSN
for this replication slot be reserved immediately; otherwise the
LSN
is reserved on first connection from a streaming replication client. Streaming changes from a physical slot is only possible with the streaming-replication protocol — see
Section 54.4
. The optional third parameter,
temporary
, 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
CREATE_REPLICATION_SLOT ... PHYSICAL
pg_drop_replication_slot
slot_name
name
) →
void
Drops the physical or logical replication slot named
slot_name
. Same as replication protocol command
DROP_REPLICATION_SLOT
pg_create_logical_replication_slot
slot_name
name
plugin
name
temporary
boolean
twophase
boolean
failover
boolean
] ) →
record
slot_name
name
lsn
pg_lsn
Creates a new logical (decoding) replication slot named
slot_name
using the output plugin
plugin
. The optional third parameter,
temporary
, 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,
twophase
, when set to true, specifies that the decoding of prepared transactions is enabled for this slot. The optional fifth parameter,
failover
, 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
CREATE_REPLICATION_SLOT ... LOGICAL
pg_copy_physical_replication_slot
src_slot_name
name
dst_slot_name
name
temporary
boolean
] ) →
record
slot_name
name
lsn
pg_lsn
Copies an existing physical replication slot named
src_slot_name
to a physical replication slot named
dst_slot_name
. The copied physical slot starts to reserve WAL from the same
LSN
as the source slot.
temporary
is optional. If
temporary
is omitted, the same value as the source slot is used. Copy of an invalidated slot is not allowed.
pg_copy_logical_replication_slot
src_slot_name
name
dst_slot_name
name
temporary
boolean
plugin
name
] ) →
record
slot_name
name
lsn
pg_lsn
Copies an existing logical replication slot named
src_slot_name
to a logical replication slot named
dst_slot_name
, optionally changing the output plugin and persistence. The copied logical slot starts from the same
LSN
as the source logical slot. Both
temporary
and
plugin
are optional; if they are omitted, the values of the source slot are used. The
failover
option of the source logical slot is not copied and is set to
false
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.
pg_logical_slot_get_changes
slot_name
name
upto_lsn
pg_lsn
upto_nchanges
integer
VARIADIC
options
text[]
) →
setof record
lsn
pg_lsn
xid
xid
data
text
Returns changes in the slot
slot_name
, starting from the point from which changes have been consumed last. If
upto_lsn
and
upto_nchanges
are NULL, logical decoding will continue until end of WAL. If
upto_lsn
is non-NULL, decoding will include only those transactions which commit prior to the specified LSN. If
upto_nchanges
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
synchronized_standby_slots
have confirmed WAL receipt.
pg_logical_slot_peek_changes
slot_name
name
upto_lsn
pg_lsn
upto_nchanges
integer
VARIADIC
options
text[]
) →
setof record
lsn
pg_lsn
xid
xid
data
text
Behaves just like the
pg_logical_slot_get_changes()
function, except that changes are not consumed; that is, they will be returned again on future calls.
pg_logical_slot_get_binary_changes
slot_name
name
upto_lsn
pg_lsn
upto_nchanges
integer
VARIADIC
options
text[]
) →
setof record
lsn
pg_lsn
xid
xid
data
bytea
Behaves just like the
pg_logical_slot_get_changes()
function, except that changes are returned as
bytea
pg_logical_slot_peek_binary_changes
slot_name
name
upto_lsn
pg_lsn
upto_nchanges
integer
VARIADIC
options
text[]
) →
setof record
lsn
pg_lsn
xid
xid
data
bytea
Behaves just like the
pg_logical_slot_peek_changes()
function, except that changes are returned as
bytea
pg_replication_slot_advance
slot_name
name
upto_lsn
pg_lsn
) →
record
slot_name
name
end_lsn
pg_lsn
Advances the current confirmed position of a replication slot named
slot_name
. 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
synchronized_standby_slots
have confirmed WAL receipt.
pg_replication_origin_create
node_name
text
) →
oid
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.
pg_replication_origin_drop
node_name
text
) →
void
Deletes a previously-created replication origin, including any associated replay progress.
pg_replication_origin_oid
node_name
text
) →
oid
Looks up a replication origin by name and returns the internal ID. If no such replication origin is found,
NULL
is returned.
pg_replication_origin_session_setup
node_name
text
) →
void
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
pg_replication_origin_session_reset
to undo.
pg_replication_origin_session_reset
() →
void
Cancels the effects of
pg_replication_origin_session_setup()
pg_replication_origin_session_is_setup
() →
boolean
Returns true if a replication origin has been selected in the current session.
pg_replication_origin_session_progress
flush
boolean
) →
pg_lsn
Returns the replay location for the replication origin selected in the current session. The parameter
flush
determines whether the corresponding local transaction will be guaranteed to have been flushed to disk or not.
pg_replication_origin_xact_setup
origin_lsn
pg_lsn
origin_timestamp
timestamp with time zone
) →
void
Marks the current transaction as replaying a transaction that has committed at the given
LSN
and timestamp. Can only be called when a replication origin has been selected using
pg_replication_origin_session_setup
pg_replication_origin_xact_reset
() →
void
Cancels the effects of
pg_replication_origin_xact_setup()
pg_replication_origin_advance
node_name
text
lsn
pg_lsn
) →
void
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.
pg_replication_origin_progress
node_name
text
flush
boolean
) →
pg_lsn
Returns the replay location for the given replication origin. The parameter
flush
determines whether the corresponding local transaction will be guaranteed to have been flushed to disk or not.
pg_logical_emit_message
transactional
boolean
prefix
text
content
text
flush
boolean
DEFAULT
false
] ) →
pg_lsn
pg_logical_emit_message
transactional
boolean
prefix
text
content
bytea
flush
boolean
DEFAULT
false
] ) →
pg_lsn
Emits a logical decoding message. This can be used to pass generic messages to logical decoding plugins through WAL. The
transactional
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
prefix
parameter is a textual prefix that can be used by logical decoding plugins to easily recognize messages that are interesting for them. The
content
parameter is the content of the message, given either in text or binary form. The
flush
parameter (default set to
false
) controls if the message is immediately flushed to WAL or not.
flush
has no effect with
transactional
, as the message's WAL record is flushed along with its transaction.
pg_sync_replication_slots
() →
void
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
Section 47.2.3
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
sync_replication_slots
is enabled and the slotsync worker is already running to perform the synchronization of slots.
Caution
If, after executing the function,
hot_standby_feedback
is disabled on the standby or the physical slot configured in
primary_slot_name
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.
9.28.7. Database Object Management Functions
The functions shown in
Table 9.102
calculate the disk space usage of database objects, or assist in presentation or understanding of usage results.
bigint
results are measured in bytes. If an OID that does not represent an existing object is passed to one of these functions,
NULL
is returned.
Table 9.102. Database Object Size Functions
Function
Description
pg_column_size
"any"
) →
integer
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.
pg_column_compression
"any"
) →
text
Shows the compression algorithm that was used to compress an individual variable-length value. Returns
NULL
if the value is not compressed.
pg_column_toast_chunk_id
"any"
) →
oid
Shows the
chunk_id
of an on-disk
TOAST
ed value. Returns
NULL
if the value is un-
TOAST
ed or not on-disk. See
Section 66.2
for more information about
TOAST
pg_database_size
name
) →
bigint
pg_database_size
oid
) →
bigint
Computes the total disk space used by the database with the specified name or OID. To use this function, you must have
CONNECT
privilege on the specified database (which is granted by default) or have privileges of the
pg_read_all_stats
role.
pg_indexes_size
regclass
) →
bigint
Computes the total disk space used by indexes attached to the specified table.
pg_relation_size
relation
regclass
fork
text
] ) →
bigint
Computes the disk space used by one
fork
of the specified relation. (Note that for most purposes it is more convenient to use the higher-level functions
pg_total_relation_size
or
pg_table_size
, 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:
main
returns the size of the main data fork of the relation.
fsm
returns the size of the Free Space Map (see
Section 66.3
) associated with the relation.
vm
returns the size of the Visibility Map (see
Section 66.4
) associated with the relation.
init
returns the size of the initialization fork, if any, associated with the relation.
pg_size_bytes
text
) →
bigint
Converts a size in human-readable format (as returned by
pg_size_pretty
) into bytes. Valid units are
bytes
kB
MB
GB
TB
, and
PB
pg_size_pretty
bigint
) →
text
pg_size_pretty
numeric
) →
text
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
= 1048576 bytes, and so on.
pg_table_size
regclass
) →
bigint
Computes the disk space used by the specified table, excluding indexes (but including its TOAST table if any, free space map, and visibility map).
pg_tablespace_size
name
) →
bigint
pg_tablespace_size
oid
) →
bigint
Computes the total disk space used in the tablespace with the specified name or OID. To use this function, you must have
CREATE
privilege on the specified tablespace or have privileges of the
pg_read_all_stats
role, unless it is the default tablespace for the current database.
pg_total_relation_size
regclass
) →
bigint
Computes the total disk space used by the specified table, including all indexes and
TOAST
data. The result is equivalent to
pg_table_size
pg_indexes_size
The functions above that operate on tables or indexes accept a
regclass
argument, which is simply the OID of the table or index in the
pg_class
system catalog. You do not have to look up the OID by hand, however, since the
regclass
data type's input converter will do the work for you. See
Section 8.19
for details.
The functions shown in
Table 9.103
assist in identifying the specific disk files associated with database objects.
Table 9.103. Database Object Location Functions
Function
Description
pg_relation_filenode
relation
regclass
) →
oid
Returns the
filenode
number currently assigned to the specified relation. The filenode is the base component of the file name(s) used for the relation (see
Section 66.1
for more information). For most relations the result is the same as
pg_class
relfilenode
, but for certain system catalogs
relfilenode
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.
pg_relation_filepath
relation
regclass
) →
text
Returns the entire file path name (relative to the database cluster's data directory,
PGDATA
) of the relation.
pg_filenode_relation
tablespace
oid
filenode
oid
) →
regclass
Returns a relation's OID given the tablespace OID and filenode it is stored under. This is essentially the inverse mapping of
pg_relation_filepath
. For a relation in the database's default tablespace, the tablespace can be specified as zero. Returns
NULL
if no relation in the current database is associated with the given values, or if dealing with a temporary relation.
Table 9.104
lists functions used to manage collations.
Table 9.104. Collation Management Functions
Function
Description
pg_collation_actual_version
oid
) →
text
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
pg_collation
collversion
, then objects depending on the collation might need to be rebuilt. See also
ALTER COLLATION
pg_database_collation_actual_version
oid
) →
text
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
pg_database
datcollversion
, then objects depending on the collation might need to be rebuilt. See also
ALTER DATABASE
pg_import_system_collations
schema
regnamespace
) →
integer
Adds collations to the system catalog
pg_collation
based on all the locales it finds in the operating system. This is what
initdb
uses; see
Section 23.2.2
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
pg_collation
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
schema
parameter would typically be
pg_catalog
, 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.
Table 9.105
lists functions used to manipulate statistics. These functions cannot be executed during recovery.
Warning
Changes made by these statistics manipulation functions are likely to be overwritten by
autovacuum
(or manual
VACUUM
or
ANALYZE
) and should be considered temporary.
Table 9.105. Database Object Statistics Manipulation Functions
Function
Description
pg_restore_relation_stats
VARIADIC
kwargs
"any"
) →
boolean
Updates table-level statistics. Ordinarily, these statistics are collected automatically or updated as a part of
VACUUM
or
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
ANALYZE
has not been run yet.
The tracked statistics may change from version to version, so arguments are passed as pairs of
argname
and
argvalue
in the form:
SELECT pg_restore_relation_stats(
arg1name
', '
arg1value
'::
arg1type
arg2name
', '
arg2value
'::
arg2type
arg3name
', '
arg3value
'::
arg3type
);
For example, to set the
relpages
and
reltuples
values for the table
mytable
SELECT pg_restore_relation_stats(
'schemaname', 'myschema',
'relname', 'mytable',
'relpages', 173::integer,
'reltuples', 10000::real);
The arguments
schemaname
and
relname
are required, and specify the table. Other arguments are the names and values of statistics corresponding to certain columns in
pg_class
. The currently-supported relation statistics are
relpages
with a value of type
integer
reltuples
with a value of type
real
relallvisible
with a value of type
integer
, and
relallfrozen
with a value of type
integer
Additionally, this function accepts argument name
version
of type
integer
, which specifies the server version from which the statistics originated. This is anticipated to be helpful in porting statistics from older versions of
PostgreSQL
Minor errors are reported as a
WARNING
and ignored, and remaining statistics will still be restored. If all specified statistics are successfully restored, returns
true
, otherwise
false
The caller must have the
MAINTAIN
privilege on the table or be the owner of the database.
pg_clear_relation_stats
schemaname
text
relname
text
) →
void
Clears table-level statistics for the given relation, as though the table was newly created.
The caller must have the
MAINTAIN
privilege on the table or be the owner of the database.
pg_restore_attribute_stats
VARIADIC
kwargs
"any"
) →
boolean
Creates or updates column-level statistics. Ordinarily, these statistics are collected automatically or updated as a part of
VACUUM
or
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
ANALYZE
has not been run yet.
The tracked statistics may change from version to version, so arguments are passed as pairs of
argname
and
argvalue
in the form:
SELECT pg_restore_attribute_stats(
arg1name
', '
arg1value
'::
arg1type
arg2name
', '
arg2value
'::
arg2type
arg3name
', '
arg3value
'::
arg3type
);
For example, to set the
avg_width
and
null_frac
values for the attribute
col1
of the table
mytable
SELECT pg_restore_attribute_stats(
'schemaname', 'myschema',
'relname', 'mytable',
'attname', 'col1',
'inherited', false,
'avg_width', 125::integer,
'null_frac', 0.5::real);
The required arguments are
schemaname
and
relname
with a value of type
text
which specify the table; either
attname
with a value of type
text
or
attnum
with a value of type
smallint
, which specifies the column; and
inherited
, which specifies whether the statistics include values from child tables. Other arguments are the names and values of statistics corresponding to columns in
pg_stats
Additionally, this function accepts argument name
version
of type
integer
, which specifies the server version from which the statistics originated. This is anticipated to be helpful in porting statistics from older versions of
PostgreSQL
Minor errors are reported as a
WARNING
and ignored, and remaining statistics will still be restored. If all specified statistics are successfully restored, returns
true
, otherwise
false
The caller must have the
MAINTAIN
privilege on the table or be the owner of the database.
pg_clear_attribute_stats
schemaname
text
relname
text
attname
text
inherited
boolean
) →
void
Clears column-level statistics for the given relation and attribute, as though the table was newly created.
The caller must have the
MAINTAIN
privilege on the table or be the owner of the database.
Table 9.106
lists functions that provide information about the structure of partitioned tables.
Table 9.106. Partitioning Information Functions
Function
Description
pg_partition_tree
regclass
) →
setof record
relid
regclass
parentrelid
regclass
isleaf
boolean
level
integer
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.
pg_partition_ancestors
regclass
) →
setof regclass
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.
pg_partition_root
regclass
) →
regclass
Returns the top-most parent of the partition tree to which the given relation belongs. Returns
NULL
if the relation does not exist or is not a partition or partitioned table.
For example, to check the total size of the data contained in a partitioned table
measurement
, one could use the following query:
SELECT pg_size_pretty(sum(pg_relation_size(relid))) AS total_size
FROM pg_partition_tree('measurement');
9.28.8. Index Maintenance Functions
Table 9.107
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.
Table 9.107. Index Maintenance Functions
Function
Description
brin_summarize_new_values
index
regclass
) →
integer
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.
brin_summarize_range
index
regclass
blockNumber
bigint
) →
integer
Summarizes the page range covering the given block, if not already summarized. This is like
brin_summarize_new_values
except that it only processes the page range that covers the given table block number.
brin_desummarize_range
index
regclass
blockNumber
bigint
) →
void
Removes the BRIN index tuple that summarizes the page range covering the given table block, if there is one.
gin_clean_pending_list
index
regclass
) →
bigint
Cleans up the
pending
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
fastupdate
option disabled, no cleanup happens and the result is zero, because the index doesn't have a pending list. See
Section 65.4.4.1
and
Section 65.4.5
for details about the pending list and
fastupdate
option.
9.28.9. Generic File Access Functions
The functions shown in
Table 9.108
provide native access to files on the machine hosting the server. Only files within the database cluster directory and the
log_directory
can be accessed, unless the user is a superuser or is granted the role
pg_read_server_files
. Use a relative path for files in the cluster directory, and a path matching the
log_directory
configuration setting for log files.
Note that granting users the EXECUTE privilege on
pg_read_file()
, 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
pg_authid
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.
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.
psql
's
\df
command can be useful to check what the actual function signatures are.
Some of these functions take an optional
missing_ok
parameter, which specifies the behavior when the file or directory does not exist. If
true
, the function returns
NULL
or an empty result set, as appropriate. If
false
, an error is raised. (Failure conditions other than
file not found
are reported as errors in any case.) The default is
false
Table 9.108. Generic File Access Functions
Function
Description
pg_ls_dir
dirname
text
missing_ok
boolean
include_dot_dirs
boolean
] ) →
setof text
Returns the names of all files (and directories and other special files) in the specified directory. The
include_dot_dirs
parameter indicates whether
and
..
are to be included in the result set; the default is to exclude them. Including them can be useful when
missing_ok
is
true
, to distinguish an empty directory from a non-existent directory.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_ls_logdir
() →
setof record
name
text
size
bigint
modification
timestamp with time zone
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.
This function is restricted to superusers and roles with privileges of the
pg_monitor
role by default, but other users can be granted EXECUTE to run the function.
pg_ls_waldir
() →
setof record
name
text
size
bigint
modification
timestamp with time zone
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.
This function is restricted to superusers and roles with privileges of the
pg_monitor
role by default, but other users can be granted EXECUTE to run the function.
pg_ls_logicalmapdir
() →
setof record
name
text
size
bigint
modification
timestamp with time zone
Returns the name, size, and last modification time (mtime) of each ordinary file in the server's
pg_logical/mappings
directory. Filenames beginning with a dot, directories, and other special files are excluded.
This function is restricted to superusers and members of the
pg_monitor
role by default, but other users can be granted EXECUTE to run the function.
pg_ls_logicalsnapdir
() →
setof record
name
text
size
bigint
modification
timestamp with time zone
Returns the name, size, and last modification time (mtime) of each ordinary file in the server's
pg_logical/snapshots
directory. Filenames beginning with a dot, directories, and other special files are excluded.
This function is restricted to superusers and members of the
pg_monitor
role by default, but other users can be granted EXECUTE to run the function.
pg_ls_replslotdir
slot_name
text
) →
setof record
name
text
size
bigint
modification
timestamp with time zone
Returns the name, size, and last modification time (mtime) of each ordinary file in the server's
pg_replslot/slot_name
directory, where
slot_name
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.
This function is restricted to superusers and members of the
pg_monitor
role by default, but other users can be granted EXECUTE to run the function.
pg_ls_summariesdir
() →
setof record
name
text
size
bigint
modification
timestamp with time zone
Returns the name, size, and last modification time (mtime) of each ordinary file in the server's WAL summaries directory (
pg_wal/summaries
). Filenames beginning with a dot, directories, and other special files are excluded.
This function is restricted to superusers and members of the
pg_monitor
role by default, but other users can be granted EXECUTE to run the function.
pg_ls_archive_statusdir
() →
setof record
name
text
size
bigint
modification
timestamp with time zone
Returns the name, size, and last modification time (mtime) of each ordinary file in the server's WAL archive status directory (
pg_wal/archive_status
). Filenames beginning with a dot, directories, and other special files are excluded.
This function is restricted to superusers and members of the
pg_monitor
role by default, but other users can be granted EXECUTE to run the function.
pg_ls_tmpdir
( [
tablespace
oid
] ) →
setof record
name
text
size
bigint
modification
timestamp with time zone
Returns the name, size, and last modification time (mtime) of each ordinary file in the temporary file directory for the specified
tablespace
. If
tablespace
is not provided, the
pg_default
tablespace is examined. Filenames beginning with a dot, directories, and other special files are excluded.
This function is restricted to superusers and members of the
pg_monitor
role by default, but other users can be granted EXECUTE to run the function.
pg_read_file
filename
text
offset
bigint
length
bigint
] [
missing_ok
boolean
] ) →
text
Returns all or part of a text file, starting at the given byte
offset
, returning at most
length
bytes (less if the end of file is reached first). If
offset
is negative, it is relative to the end of the file. If
offset
and
length
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.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
pg_read_binary_file
filename
text
offset
bigint
length
bigint
] [
missing_ok
boolean
] ) →
bytea
Returns all or part of a file. This function is identical to
pg_read_file
except that it can read arbitrary binary data, returning the result as
bytea
not
text
; accordingly, no encoding checks are performed.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
In combination with the
convert_from
function, this function can be used to read a text file in a specified encoding and convert to the database's encoding:
SELECT convert_from(pg_read_binary_file('file_in_utf8.txt'), 'UTF8');
pg_stat_file
filename
text
missing_ok
boolean
] ) →
record
size
bigint
access
timestamp with time zone
modification
timestamp with time zone
change
timestamp with time zone
creation
timestamp with time zone
isdir
boolean
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.
This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.
9.28.10. Advisory Lock Functions
The functions shown in
Table 9.109
manage advisory locks. For details about proper use of these functions, see
Section 13.3.5
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
false
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.
Table 9.109. Advisory Lock Functions
Function
Description
pg_advisory_lock
key
bigint
) →
void
pg_advisory_lock
key1
integer
key2
integer
) →
void
Obtains an exclusive session-level advisory lock, waiting if necessary.
pg_advisory_lock_shared
key
bigint
) →
void
pg_advisory_lock_shared
key1
integer
key2
integer
) →
void
Obtains a shared session-level advisory lock, waiting if necessary.
pg_advisory_unlock
key
bigint
) →
boolean
pg_advisory_unlock
key1
integer
key2
integer
) →
boolean
Releases a previously-acquired exclusive session-level advisory lock. Returns
true
if the lock is successfully released. If the lock was not held,
false
is returned, and in addition, an SQL warning will be reported by the server.
pg_advisory_unlock_all
() →
void
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.)
pg_advisory_unlock_shared
key
bigint
) →
boolean
pg_advisory_unlock_shared
key1
integer
key2
integer
) →
boolean
Releases a previously-acquired shared session-level advisory lock. Returns
true
if the lock is successfully released. If the lock was not held,
false
is returned, and in addition, an SQL warning will be reported by the server.
pg_advisory_xact_lock
key
bigint
) →
void
pg_advisory_xact_lock
key1
integer
key2
integer
) →
void
Obtains an exclusive transaction-level advisory lock, waiting if necessary.
pg_advisory_xact_lock_shared
key
bigint
) →
void
pg_advisory_xact_lock_shared
key1
integer
key2
integer
) →
void
Obtains a shared transaction-level advisory lock, waiting if necessary.
pg_try_advisory_lock
key
bigint
) →
boolean
pg_try_advisory_lock
key1
integer
key2
integer
) →
boolean
Obtains an exclusive session-level advisory lock if available. This will either obtain the lock immediately and return
true
, or return
false
without waiting if the lock cannot be acquired immediately.
pg_try_advisory_lock_shared
key
bigint
) →
boolean
pg_try_advisory_lock_shared
key1
integer
key2
integer
) →
boolean
Obtains a shared session-level advisory lock if available. This will either obtain the lock immediately and return
true
, or return
false
without waiting if the lock cannot be acquired immediately.
pg_try_advisory_xact_lock
key
bigint
) →
boolean
pg_try_advisory_xact_lock
key1
integer
key2
integer
) →
boolean
Obtains an exclusive transaction-level advisory lock if available. This will either obtain the lock immediately and return
true
, or return
false
without waiting if the lock cannot be acquired immediately.
pg_try_advisory_xact_lock_shared
key
bigint
) →
boolean
pg_try_advisory_xact_lock_shared
key1
integer
key2
integer
) →
boolean
Obtains a shared transaction-level advisory lock if available. This will either obtain the lock immediately and return
true
, or return
false
without waiting if the lock cannot be acquired immediately.
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9.27. System Information Functions and Operators
9.29. Trigger Functions
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