Backup and Restoration Control Functions

Backup Control Functions

Backup control functions help online backup.

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.
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.

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.

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.
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.
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. For example:

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
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
pg_disable_delay_xlog_recycle()
Description: Disables Xlog recycle delay.

Return type: void

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:

**Table 1** pgxc_get_senders_catchup_time() columns
Name	Type	Description
node_name	text	Node name
lwpid	integer	Current sender lwpid
local_role	text	Local role
peer_role	text	Peer role
state	text	Current sender's replication status
sender	text	Current sender type
catchup_start	timestamp with time zone	Startup time of a catchup task
catchup_end	timestamp with time zone	End time of a catchup task
catchup_type	text	Catchup task type, full or incremental
catchup_bcm_filename	text	BCM file executed by the current catchup task
catchup_bcm_finished	integer	Number of BCM files completed by a catchup task
catchup_bcm_total	integer	Total number of BCM files to be operated by a catchup task
catchup_percent	text	Completion percentage of a catchup task
catchup_remaining_time	text	Estimated remaining time of a catchup task

Restoration Control Functions

Restoration control functions provide information about the status of standby nodes. These functions may be executed both during restoration and in normal running.

pg_is_in_recovery()
Description: Returns true if restoration is still in progress.

Return type: bool
pg_last_xlog_receive_location()
Description: Gets the last transaction log location received and synchronized to disk by streaming replication. While streaming replication is in progress, this will increase monotonically. If restoration has completed, then this value will remain static at the value of the last WAL record received and synchronized to disk during restoration. If streaming replication is disabled or if not yet started, the function return will return NULL.

Return type: text
pg_last_xlog_replay_location()
Description: Gets last transaction log location replayed during restoration. If restoration is still in progress, this will increase monotonically. If restoration has completed, then this value will remain static at the value of the last WAL record received during that restoration. When the server has been started normally without restoration, the function returns NULL.

Return type: text
pg_last_xact_replay_timestamp()
Description: Gets the timestamp of last transaction replayed during restoration. This is the time to commit a transaction or abort a WAL record on the primary node. If no transactions have been replayed during restoration, this function will return NULL. Otherwise, if restoration is still in progress, this will increase monotonically. If restoration has completed, then this value will remain static at the value of the last WAL record received during that restoration. If the server normally starts without manual intervention, this function will return NULL.

Return type: timestamp with time zone

Restoration control functions control restoration processes. These functions may be executed only during restoration.

pg_is_xlog_replay_paused()
Description: Returns true if restoration is paused.

Return type: bool
pg_xlog_replay_pause()
Description: Pauses restoration immediately.

Return type: void
pg_xlog_replay_resume()
Description: Restarts restoration if it was paused.

Return type: void

While restoration is paused, no further database changes are applied. In hot standby mode, all new queries will see the same consistent snapshot of the database, and no further query conflicts will be generated until restoration is resumed.

If streaming replication is disabled, the paused state may continue indefinitely without problem. While streaming replication is in progress, WAL records will continue to be received, which will eventually fill available disk space. This progress depends on the duration of the pause, the rate of WAL generation, and available disk space.

pg_xlog_replay_completion()

Description: Displays the progress of xlog redo on the current DN.

Return type: record

The following information is returned:

**Table 2** pg_xlog_replay_completion() columns
Column	Type	Description
replay_start	integer	Start LSN of xlog redo
replay_current	integer	LSN of the current replay of xlog redo
replay_end	integer	Maximum LSN that requires xlog redo
replay_percent	integer	Completion percentage of xlog redo

pg_data_sync_from_dummy_completion()

Description: Displays the progress of data page file synchronization during the failover on the current DN.

Return type: record

The following information is returned:

**Table 3** pg_data_sync_from_dummy_completion() columns
Column	Type	Description
start_index	integer	Start LSN of data page file synchronization
current_index	integer	Current LSN of data page file synchronization
total_index	integer	Maximum LSN of data page file synchronization
sync_percent	integer	Completion percentage of data page files

gs_roach_stop_backup(backupid text)
Description: Stops a backup started by the internal backup tool GaussRoach and returns the position where the current log is inserted. This function is similar to pg_stop_backup, but is more lightweight.

Return type: text
gs_roach_enable_delay_ddl_recycle(backupid name)
Description: Enables DDL delay and returns the log position of the enabling point. This function is similar to pg_enable_delay_ddl_recycle, but is more lightweight. In addition, this function allows you to enable DDL delay for multiple backups.

Return type: text
gs_roach_disable_delay_ddl_recycle(backupid text)
Description: Disables DDL delay, returns the logs for which DDL delay takes effect, and deletes the physical files of the column-store tables that have been deleted by the user. This function is similar to pg_enable_delay_ddl_recycle, but is more lightweight. In addition, this function allows you to disable DDL delay for multiple backups.

Return type: record
gs_roach_switch_xlog(request_ckpt bool)
Description: Switches the currently used log segment file and returns the position of the segment log. If the value of request_ckpt is true, a full check point is triggered.

Return type: text
pg_resume_bkp_flag(backupid name)
Description: Resumes the delay xlog flag from a specified backup and returns start_backup_flag boolean, to_delay boolean, ddl_delay_recycle_ptr text, and rewind_time text.

Return type: record