# 9.27. System Administration Functions
9.27.1. Configuration Settings Functions
9.27.2. Server Signaling Functions
9.27.3. Backup Control Functions
9.27.4. Recovery Control Functions
9.27.5. Snapshot Synchronization Functions
9.27.6. Replication Management Functions
9.27.7. Database Object Management Functions
9.27.8. Index Maintenance Functions
9.27.9. Generic File Access Functions
9.27.10. Advisory Lock Functions
The functions described in this section are used to control and monitor a PostgreSQL installation.
# 9.27.1. Configuration Settings Functions
Table 9.85 shows the functions available to query and alter run-time configuration parameters.
Table 9.85. Configuration Settings Functions
| Function Description Example(s) |
|---|
current_setting ( setting_name text [, missing_ok boolean ] ) → textReturns 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 ) → textSets 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('log_statement_stats', 'off', false) → off |
# 9.27.2. Server Signaling Functions
The functions shown in Table 9.86 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 9.86. Server Signaling Functions
| Function Description |
|---|
pg_cancel_backend ( pid integer ) → booleanCancels 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 been granted pg_signal_backend, however only superusers can cancel superuser backends. |
pg_log_backend_memory_contexts ( pid integer ) → booleanRequests to log the memory contexts of the backend with the specified process ID. 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 20.8 for more information), but will not be sent to the client regardless of client_min_messages. Only superusers can request to log the memory contexts. |
pg_reload_conf () → booleanCauses 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 and pg_hba_file_rules views to check the configuration files for possible errors, before reloading. |
pg_rotate_logfile () → booleanSignals 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 0 ) → booleanTerminates 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 been granted pg_signal_backend, however only superusers can terminate 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
### 9.27.3. Backup Control Functions
[]()
The functions shown in [Table 9.87](functions-admin.html#FUNCTIONS-ADMIN-BACKUP-TABLE) assist in making on-line backups. These functions cannot be executed during recovery (except non-exclusive `pg_start_backup`, non-exclusive `pg_stop_backup`, `pg_is_in_backup`, `pg_backup_start_time` and `pg_wal_lsn_diff`).
For details about proper usage of these functions, see [Section 26.3](continuous-archiving.html).
**Table 9.87. Backup Control Functions**
| Function<br/><br/> Description |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| []() `pg_create_restore_point` ( *`name`* `text` ) → `pg_lsn`<br/><br/> 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](runtime-config-wal.html#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.<br/><br/> 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`<br/><br/> Returns the current write-ahead log flush location (see notes below). |
| []() `pg_current_wal_insert_lsn` () → `pg_lsn`<br/><br/> Returns the current write-ahead log insert location (see notes below). |
| []() `pg_current_wal_lsn` () → `pg_lsn`<br/><br/> Returns the current write-ahead log write location (see notes below). |
| []() `pg_start_backup` ( *`label`* `text` [, *`fast`* `boolean` [, *`exclusive`* `boolean` ]] ) → `pg_lsn`<br/><br/> 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_start_backup` as quickly as possible. This forces an immediate checkpoint which will cause a spike in I/O operations, slowing any concurrently executing queries. The optional third parameter specifies whether to perform an exclusive or non-exclusive backup (default is exclusive).<br/><br/> When used in exclusive mode, this function writes a backup label file (`backup_label`) and, if there are any links in the `pg_tblspc/` directory, a tablespace map file (`tablespace_map`) into the database cluster's data directory, then performs a checkpoint, and then returns the backup's starting write-ahead log location. (The user can ignore this result value, but it is provided in case it is useful.) When used in non-exclusive mode, the contents of these files are instead returned by the `pg_stop_backup` function, and should be copied to the backup area by the user.<br/><br/> This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function. |
|[]() `pg_stop_backup` ( *`exclusive`* `boolean` [, *`wait_for_archive`* `boolean` ] ) → `setof record` ( *`lsn`* `pg_lsn`, *`labelfile`* `text`, *`spcmapfile`* `text` )<br/><br/> Finishes performing an exclusive or non-exclusive on-line backup. The *`exclusive`* parameter must match the previous `pg_start_backup` call. In an exclusive backup, `pg_stop_backup` removes the backup label file and, if it exists, the tablespace map file created by `pg_start_backup`. In a non-exclusive backup, the desired contents of these files are returned as part of the result of the function, and should be written to files in the backup area (not in the data directory).<br/><br/> There is an optional second 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_stop_backup` 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.)<br/><br/> 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_start_backup`, 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.<br/><br/> 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 and third columns are `NULL` when ending an exclusive backup; after a non-exclusive backup they hold the desired contents of the label and tablespace map files.<br/><br/> This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function.|
| `pg_stop_backup` () → `pg_lsn`<br/><br/> Finishes performing an exclusive on-line backup. This simplified version is equivalent to `pg_stop_backup(true, true)`, except that it only returns the `pg_lsn` result.<br/><br/> This function is restricted to superusers by default, but other users can be granted EXECUTE to run the function. |
| []() `pg_is_in_backup` () → `boolean`<br/><br/> Returns true if an on-line exclusive backup is in progress. |
| []() `pg_backup_start_time` () → `timestamp with time zone`<br/><br/> Returns the start time of the current on-line exclusive backup if one is in progress, otherwise `NULL`. |
| []() `pg_switch_wal` () → `pg_lsn`<br/><br/> 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.<br/><br/> 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`<br/><br/> 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` )<br/><br/> Converts a write-ahead log location to a WAL file name and byte offset within that file. |
| []() `pg_wal_lsn_diff` ( *`lsn1`* `pg_lsn`, *`lsn2`* `pg_lsn` ) → `numeric`<br/><br/> 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 9.87](functions-admin.html#FUNCTIONS-ADMIN-BACKUP-TABLE) 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_stop_backup()); file_name | file_offset
# 9.27.4. Recovery Control Functions
The functions shown in Table 9.88 provide information about the current status of a standby server. These functions may be executed both during recovery and in normal running.
Table 9.88. Recovery Information Functions
The functions shown in Table 9.89 control the progress of recovery. These functions may be executed only during recovery.
Table 9.89. Recovery Control Functions
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.
# 9.27.5. 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 9.90, and imported with the SET TRANSACTION command.
Table 9.90. Snapshot Synchronization Functions
| Function Description |
|---|
pg_export_snapshot () → textSaves 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. |
# 9.27.6. Replication Management Functions
The functions shown in Table 9.91 are for controlling and interacting with replication features. See Section 27.2.5, Section 27.2.6, and Chapter 50 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 53.4.
The functions described in Section 9.27.3, Section 9.27.4, and Section 9.27.5 are also relevant for replication.
Table 9.91. 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 53.4. 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 ) → voidDrops the physical or logical replication slot named slot_name. Same as replication protocol command DROP_REPLICATION_SLOT. For logical slots, this must be called while connected to the same database the slot was created on. |
pg_create_logical_replication_slot ( slot_name name, plugin name [, temporary boolean, two_phase 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, two_phase, when set to true, specifies that the decoding of prepared transactions is enabled for this slot. A call to this function has the same effect as the replication protocol command 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. |
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. |
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. |
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. |
pg_replication_origin_create ( node_name text ) → oidCreates a replication origin with the given external name, and returns the internal ID assigned to it. |
pg_replication_origin_drop ( node_name text ) → voidDeletes a previously-created replication origin, including any associated replay progress. |
pg_replication_origin_oid ( node_name text ) → oidLooks 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 ) → voidMarks 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 () → voidCancels the effects of pg_replication_origin_session_setup(). |
pg_replication_origin_session_is_setup () → booleanReturns true if a replication origin has been selected in the current session. |
pg_replication_origin_session_progress ( flush boolean ) → pg_lsnReturns 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 ) → voidMarks 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 () → voidCancels the effects of pg_replication_origin_xact_setup(). |
pg_replication_origin_advance ( node_name text, lsn pg_lsn ) → voidSets 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_lsnReturns 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 ) → pg_lsnpg_logical_emit_message ( transactional boolean, prefix text, content bytea ) → pg_lsnEmits 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. |
# 9.27.7. Database Object Management Functions
The functions shown in Table 9.92 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 9.92. Database Object Size Functions
| Function Description |
|---|
pg_column_size ( "any" ) → integerShows 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" ) → textShows the compression algorithm that was used to compress an individual variable-length value. Returns NULL if the value is not compressed. |
pg_database_size ( name ) → bigintpg_database_size ( oid ) → bigintComputes 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 be a member of the pg_read_all_stats role. |
pg_indexes_size ( regclass ) → bigintComputes the total disk space used by indexes attached to the specified table. |
pg_relation_size ( relation regclass [, fork text ] ) → bigintComputes 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 70.3) associated with the relation.* vm returns the size of the Visibility Map (see Section 70.4) associated with the relation.* init returns the size of the initialization fork, if any, associated with the relation. |
pg_size_bytes ( text ) → bigintConverts a size in human-readable format (as returned by pg_size_pretty) into bytes. |
pg_size_pretty ( bigint ) → textpg_size_pretty ( numeric ) → textConverts a size in bytes into a more easily human-readable format with size units (bytes, kB, MB, GB or TB as appropriate). Note that the units are powers of 2 rather than powers of 10, so 1kB is 1024 bytes, 1MB is 10242 = 1048576 bytes, and so on. |
pg_table_size ( regclass ) → bigintComputes 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 ) → bigintpg_tablespace_size ( oid ) → bigintComputes 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 be a member of the pg_read_all_stats role, unless it is the default tablespace for the current database. |
pg_total_relation_size ( regclass ) → bigintComputes 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 9.93 assist in identifying the specific disk files associated with database objects.
Table 9.93. Database Object Location Functions
| Function Description |
|---|
pg_relation_filenode ( relation regclass ) → oidReturns 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 70.1 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 ) → textReturns the entire file path name (relative to the database cluster's data directory, PGDATA) of the relation. |
pg_filenode_relation ( tablespace oid, filenode oid ) → regclassReturns 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. |
Table 9.94 lists functions used to manage collations.
Table 9.94. Collation Management Functions
| Function Description |
|---|
pg_collation_actual_version ( oid ) → textReturns 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_import_system_collations ( schema regnamespace ) → integerAdds 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 24.2.2 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 9.95 lists functions that provide information about the structure of partitioned tables.
Table 9.95. Partitioning Information Functions
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');
# 9.27.8. Index Maintenance Functions
Table 9.96 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 9.96. Index Maintenance Functions
| Function Description |
|---|
brin_summarize_new_values ( index regclass ) → integerScans 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 ) → integerSummarizes 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 ) → voidRemoves the BRIN index tuple that summarizes the page range covering the given table block, if there is one. |
gin_clean_pending_list ( index regclass ) → bigintCleans 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 67.4.1 and Section 67.5 for details about the pending list and fastupdate option. |
# 9.27.9. Generic File Access Functions
The functions shown in Table 9.97 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.
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. The default is false.
Table 9.97. Generic File Access Functions
# 9.27.10. Advisory Lock Functions
The functions shown in Table 9.98 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 9.98. Advisory Lock Functions