On Mon, Jan 17, 2022 at 8:14 PM Thom Brown <t...@linux.com> wrote: > > Hi, > > Should archive_command being blank when archiving is enabled result in > a fatal error? This doesn't even produce a warning when restarting, > just an entry in the log when it goes to archive a WAL segment, and > finds the archive_command is empty. > > Is there a valid scenario where someone would have archiving enabled > but no archive command? Naturally it will build up WAL until it is > corrected, which will result in a less desirable error, and likely at > a less convenient time, and to avoid it, someone either has to have > checked the logs and noticed this error, or got curious as to why > their WAL collection is nearly running out of shelf space.
Yes, the .ready files under archive_status and wal files under pg_wal directory grow up with archive_mode on but no archive_command. The archiver keeps emitting "archive_mode enabled, yet archive_command is not set" warnings into server logs, maybe this is something that needs to be monitored for. The expectation is to have a good archiving configuration setup in place which updates both archive_command and archive_mode to appropriate values. The server keeps the WAL files from the point when archive_mode is enabled, but not from the point when the archive_command is set. The archive_mode needs postmaster restart whereas archive_command doesn't, if the archive_command too needed a postmaster restart, then we would have failed FATALly if archive_command was empty. But making the archive_command a needs-postmaster-restart class of parameter is not the path we go IMO because avoiding pomaster restarts in production environments is to be avoided whenever possible. An extreme scenario I can think of is if the archive_command is set to empty by a service layer code. Of course, this is something postgres doesn't need to care about. However, a reasonable thing to do is to emit a WARNING or ERROR-out when archive_command is set to null in it's check_archive_command when archive_mode is on? Regards, Bharath Rupireddy.
