On Wed, May 11, 2011 at 1:12 PM, Josh Berkus <josh@agliodbs.com> wrote:
> For 9.1, both master and replica in a sync replication relationship are
> required to be fsync'ing to disk. I understand why we had to do that
> for our first cut at synch rep. Do you think, though, that it might
> become possible to replicate without synch-to-disk for 9.2?
>
> The use case I have is cloud hosting, where I'd rather have two or three
> synchronous standbys than synch to disk.
It's already possible to set fsync=off on the standby if you want. If
there is an OS-level crash you'll need to rebuild the standby, but in
some cases that may be acceptable.
And Simon has already written a patch to add a "receive" mode to sync
rep, which I expected will get committed to 9.2. In that mode, the
standby can acknowledge the WAL records as soon as they are received,
and write them to disk just after. I think we do need some
benchmarking there, to figure out whether any changes to the timing of
replies are needed in that case. But the basic principal seems sound.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company