Re: Blank archive_command

On Mon, 17 Jan 2022 at 15:25, Bharath Rupireddy
<bharath.rupireddyforpostgres@gmail.com> wrote:
>
> On Mon, Jan 17, 2022 at 8:14 PM Thom Brown <thom@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.

Okay, that makes sense.  Thanks.  I guess people have to be careful
with their settings.  I was hoping there was one less footgun that
could be disarmed.
>
> 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.



-- 
Thom