On Mon, Oct 29, 2012 at 10:23 AM, Claudio Freire <klaussfre...@gmail.com>wrote:
> On Mon, Oct 29, 2012 at 9:09 AM, Matheus de Oliveira > <matioli.math...@gmail.com> 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). > > I imagine it's automatic. 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
