Backup Control Functions

pg_create_restore_point(name text)

Description: Creates a named point for performing the restore operation (restricted to system administrators).

Return type: text

Note: pg_create_restore_point creates a named transaction log record that can be used as a restoration target, and returns the corresponding transaction log location. The given name can then be used with recovery_target_name to specify the point up to which restoration will proceed. Avoid creating multiple restoration points with the same name, since restoration will stop at the first one whose name matches the restoration target.

pg_current_xlog_location()

Description: Obtains the write position of the current transaction log.

Return type: text

Note: pg_current_xlog_location displays the write position of the current transaction log in the same format as those of the previous functions. Read-only operations do not require rights of the system administrator.

Example:

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 SELECT pg_current_xlog_location();
 pg_current_xlog_location
--------------------------
 0/4310D5D8
(1 row)

pg_current_xlog_insert_location()

Description: Obtains the insert position of the current transaction log.

Return type: text

Note: pg_current_xlog_insert_location displays the insert position of the current transaction log. The insertion point is the logical end of the transaction log at any instant, while the write location is the end of what has been written out from the server's internal buffers. The write position is the end that can be detected externally from the server. This operation can be performed to archive only some of completed transaction log files. The insert position is mainly used for commissioning the server. Read-only operations do not require rights of the system administrator.

Example:

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 SELECT pg_current_xlog_insert_location();
 pg_current_xlog_insert_location
---------------------------------
 0/4316AD50
(1 row)

pg_start_backup(label text [, fast boolean ])

Description: Starts executing online backup (restricted to system administrators or replication roles).

Return type: text

Note: pg_start_backup receives a user-defined backup label (usually the name of the position where the backup dump file is stored). This function writes a backup label file to the data directory of the database cluster and then returns the starting position of backed up transaction logs in text mode.

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SELECT pg_start_backup('label_goes_here');
 pg_start_backup
-----------------
 0/3000020
(1 row)

pg_stop_backup()

Description: Completes online backup (restricted to system administrators or replication roles).

Return type: text

Note: pg_stop_backup deletes the label file created by pg_start_backup and creates a backup history file in the transaction log archive area. The history file includes the label given to pg_start_backup, the starting and ending transaction log locations for the backup, and the starting and ending times of the backup. The return value is the backup's ending transaction log location. After the ending position is calculated, the insert position of the current transaction log automatically goes ahead to the next transaction log file. This way, the ended transaction log file can be immediately archived so that backup is complete.

Example:

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 SELECT pg_stop_backup();
 pg_stop_backup
----------------
 0/4401E610
(1 row)

pg_switch_xlog()

Description: Switches to a new transaction log file (restricted to system administrators).

Return type: text

Note: pg_switch_xlog moves to the next transaction log file so that the current log file can be archived (if continuous archive is used). The return value is the ending transaction log location + 1 within the just-completed transaction log file. If there has been no transaction log activity since the last transaction log switchover, pg_switch_xlog will do nothing but return the start location of the transaction log file currently in use.

Example:

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SELECT pg_switch_xlog();
 pg_switch_xlog
----------------
 0/45017978
(1 row)

pg_xlogfile_name(location text)

Description: Converts the position string in a transaction log to a file name.

Return type: text

Note: pg_xlogfile_name extracts only the transaction log file name. If the given transaction log position is the transaction log file border, a transaction log file name will be returned for both the two functions. This is usually the desired behavior for managing transaction log archiving, since the preceding file is the last one that currently needs to be archived.

pg_xlogfile_name_offset(location text)

Description: Converts the position string in a transaction log to a file name and returns the byte offset in the file.

Return type: text, integer

Note: pg_xlogfile_name_offset can extract transaction log file names and byte offsets from the returned results of the preceding functions. Example:

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SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
NOTICE:  pg_stop_backup cleanup done, waiting for required WAL segments to be archived
NOTICE:  pg_stop_backup complete, all required WAL segments have been archived
        file_name         | file_offset 
--------------------------+-------------
000000010000000000000003  |         272
(1 row)

pg_xlog_location_diff(location text, location text)

Description: pg_xlog_location_diff calculates the difference in bytes between two transaction log locations.

Return type: numeric

pg_cbm_tracked_location()

Description: Queries for the LSN location parsed by CBM.

Return type: text

pg_cbm_get_merged_file(startLSNArg text, endLSNArg text)

Description: Combines CBM files within the specified LSN range into one and returns the name of the combined file.

Return type: text

pg_cbm_get_changed_block(startLSNArg text, endLSNArg text)

Description: Combines CBM files within the specified LSN range into a table and return records of this table.

Return type: record

Note: The table columns include the start LSN, end LSN, tablespace OID, database OID, table relfilenode, table fork number, whether the table is deleted, whether the table is created, whether the table is truncated, number of pages in the truncated table, number of modified pages, and list of No. of modified pages.

pg_cbm_recycle_file(slotName name, targetLSNArg text)

Description: Deletes the CBM files that are no longer used and returns the first LSN after the deletion. If slotName is empty, targetLSNArg is used as the recycling point. During backup and DR, you need to specify a slot name due to parallelism. Record the targetLSNArg value of the task to the slot, traverse all backup slots, and find the smallest LSN as the recycling point.

Return type: text

pg_cbm_force_track(targetLSNArg text,timeOut int)

Description: Forcibly executes the CBM trace to the specified Xlog position and returns the Xlog position of the actual trace end point.

Return type: text

pg_enable_delay_ddl_recycle()

Description: Enables DDL delay and returns the Xlog position of the enabling point.

Return type: text

Example:

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SELECT pg_enable_delay_ddl_recycle();
 pg_enable_delay_ddl_recycle
-----------------------------
 00000000/4607B250
(1 row)

pg_disable_delay_ddl_recycle(barrierLSNArg text, isForce bool)

Description: Disables DDL delay and returns the Xlog range where DDL delay takes effect.

Return type: record

pg_enable_delay_xlog_recycle()

Description: Enables Xlog recycle delay.

Return type: void

Example:

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SELECT pg_enable_delay_xlog_recycle();
 pg_enable_delay_xlog_recycle
------------------------------

(1 row)

pg_disable_delay_xlog_recycle()

Description: Disables Xlog recycle delay.

Return type: void

Example:

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SELECT pg_disable_delay_xlog_recycle();
 pg_disable_delay_xlog_recycle
-------------------------------

(1 row)

pgxc_get_senders_catchup_time()

Description: Displays the catchup information of the currently active primary/standby instance sending thread on all DNs.

Return type: record

The following information is returned:

pgxc_lock_for_backup()

Description: Locks the cluster before backup. Backup is performed to restore data on new nodes.

Return type: boolean

pgxc_lock_for_backup locks a cluster before gs_dump or gs_dumpall is used to back up the cluster. After a cluster is locked, operations changing the system structure are not allowed. This function does not affect DML statements.

Example:

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SELECT pgxc_lock_for_backup();
 pgxc_lock_for_backup
----------------------
 t
(1 row)