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26.1. Archive Recovery Settings

restore_command (string)

The shell command to execute to retrieve an archived segment of the WAL file series. This parameter is required for archive recovery, but optional for streaming replication. Any %f in the string is replaced by the name of the file to retrieve from the archive, and any %p is replaced by the copy destination path name on the server. (The path name is relative to the current working directory, i.e., the cluster's data directory.) Any %r is replaced by the name of the file containing the last valid restart point. That is the earliest file that must be kept to allow a restore to be restartable, so this information can be used to truncate the archive to just the minimum required to support restarting from the current restore. %r is typically only used by warm-standby configurations (see Section 25.2). Write %% to embed an actual % character.

It is important for the command to return a zero exit status only if it succeeds. The command will be asked for file names that are not present in the archive; it must return nonzero when so asked. Examples:

restore_command = 'cp /mnt/server/archivedir/%f "%p"'
restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
archive_cleanup_command (string)

This optional parameter specifies a shell command that will be executed at every restartpoint. The purpose of archive_cleanup_command is to provide a mechanism for cleaning up old archived WAL files that are no longer needed by the standby server. Any %r is replaced by the name of the file containing the last valid restart point. That is the earliest file that must be kept to allow a restore to be restartable, and so all files earlier than %r may be safely removed. This information can be used to truncate the archive to just the minimum required to support restart from the current restore. The pg_archivecleanup module is often used in archive_cleanup_command for single-standby configurations, for example:

archive_cleanup_command = 'pg_archivecleanup /mnt/server/archivedir %r'

Note however that if multiple standby servers are restoring from the same archive directory, you will need to ensure that you do not delete WAL files until they are no longer needed by any of the servers. archive_cleanup_command would typically be used in a warm-standby configuration (see Section 25.2). Write %% to embed an actual % character in the command.

If the command returns a non-zero exit status then a WARNING log message will be written.

recovery_end_command (string)

This parameter specifies a shell command that will be executed once only at the end of recovery. This parameter is optional. The purpose of the recovery_end_command is to provide a mechanism for cleanup following replication or recovery. Any %r is replaced by the name of the file containing the last valid restart point, like in archive_cleanup_command.

If the command returns a non-zero exit status then a WARNING log message will be written and the database will proceed to start up anyway. An exception is that if the command was terminated by a signal, the database will not proceed with startup.

Comments


Artur Linhart
Sept. 15, 2012, 4:20 p.m.

Unfortunatelly, there is, for now, no possibility to set something like wal_restore_delay - the delay after the WALRestore process is called again in the case of the standby configuration to call the restore command.

Currently, the WALRestore process is called every 10 seconds, so also the restore command should to be issued every 10 seconds.

(see http://archives.postgresql.org/pgsql-hackers/2012-01/msg01361.php or http://archives.postgresql.org/pgsql-hackers/2012-01/msg01473.php )

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