On Mon, Oct 29, 2012 at 10:23 AM, Claudio Freire <klaussfreire@xxxxxxxxx> wrote:
If you don't set restore_command *and* get more segments than max_wal_keep_segments, PostgreSQL will not read the archived segments (it does not even know where it is actually).
On Mon, Oct 29, 2012 at 9:09 AM, Matheus de OliveiraI imagine it's automatic.
<matioli.matheus@xxxxxxxxx> wrote:
>> > If you have incremental backup, a restore_command on recovery.conf seems
>> > better than running rsync again when the slave get out of sync. Doesn't
>> > it?
>>
>> What do you mean?
>>
>> Usually, when it falls out of sync like that, it's because the
>> database is undergoing structural changes, and the link between master
>> and slave (both streaming and WAL shipping) isn't strong enough to
>> handle the massive rewrites. A backup is of no use there either. We
>> could make the rsync part of a recovery command, but we don't want to
>> be left out of the loop so we prefer to do it manually. As noted, it
>> always happens when someone's doing structural changes so it's not
>> entirely unexpected.
>>
>> Or am I missing some point?
>
>
> What I meant is that *if* you save you log segments somewhere (with
> archive_command), you can always use the restore_command on the slave side
> to catch-up with the master, even if streaming replication failed and you
> got out of sync. Of course if you structural changes is *really big*,
> perhaps recovering from WAL archives could even be slower than rsync (I
> really think it's hard to happen though).
If you don't set restore_command *and* get more segments than max_wal_keep_segments, PostgreSQL will not read the archived segments (it does not even know where it is actually).
We have WAL shipping in place, but even that
gets out of sync (more segments generated than our quota on the
archive allows - we can't really keep more since we lack the space on
the server we put them).
Yeah, in that case there is no way. If you cannot keep *all* segments during your "structural changes" you will have to go with a rsync (or something similar).
But that's an option for you to know, *if* you have enough segments, than it is possible to restore from them. In some customers of mine (with little disk space) I even don't set max_wal_keep_segments too high, and prefer to "keep" the segments with archive_command, but that's not the better scenario.
Regards,
--
Matheus de Oliveira
Analista de Banco de Dados PostgreSQL
Dextra Sistemas - MPS.Br nível F!
www.dextra.com.br/postgres
