archive_command
archive_command is a configuration parameter which determines how completed WAL segments are sent to archive storage.
archive_command was added in PostgreSQL 8.0.
Usage
archive_mode must be set to on (PostgreSQL 9.5 and later: optionally always) for archive_command to be recognised.
Disabling WAL archiving
As archive_mode requires a PostgreSQL restart for changes to become effective, the recommended method of temporarily disabling WAL archiving is to set archive_command to an empty string (''), which will cause the command to fail. Archiving will resume onece a valid archive_command is set.
If archive_command is set to an arbitrary command which returns a zero exit status (success), e.g. /bin/true, WAL files ready for archiving will be removed without being archived. This also effectively disables archiving, but means there will be a break in the chain of archived WAL files, and unless the files are archived by another route, the archive will only be valid up until the last file archived before the archiving chain was broken.
Diagnosing issues
From PostgreSQL 9.4, the system catalogue view pg_stat_archiver can be used to determine if archive_command is failing.
Precise details of the failure can be found in the PostgreSQL log file and will look something like this:
[2019-06-10 21:51:43 UTC] node2 postgres [unknown] LOCATION: ProcessStandbyReplyMessage, walsender.c:1788 cp: cannot create regular file "/home/backup/invalid-wal-dir/000000010000000000000001": No such file or directory [2019-06-10 21:51:44 UTC] LOG: 00000: archive command failed with exit code 1 [2019-06-10 21:51:44 UTC] DETAIL: The failed archive command was: test ! -f /home/backup/invalid-wal-dir/000000010000000000000001 && cp pg_wal/000000010000000000000001 /home/backup/invalid-wal-dir/000000010000000000000001
Change history
- PostgreSQL 8.0
- added (commit 66ec2db7)
References
- PostgreSQL documentation: archive_command