On 10/06/2010 08:31 AM, Heikki Linnakangas wrote: > On 06.10.2010 01:14, Josh Berkus wrote: >> Last I checked, our goal with synch standby was to increase availablity, >> not decrease it. > > No. Synchronous replication does not help with availability. It allows > you to achieve zero data loss, ie. if the master dies, you are > guaranteed that any transaction that was acknowledged as committed, is > still committed.
Strictly speaking, it even reduces availability. Which is why nobody actually wants *only* synchronous replication. Instead they use quorum commit or semi-synchronous (shudder) replication, which only requires *some* nodes to be in sync, but effectively replicates asynchronously to the others. >From that point of view, the requirement of having one synch and two async standbies is pretty much the same as having three synch standbies with a quorum commit of 1. (Except for additional availability of the later variant, because in case of a failure of the one sync standby, any of the others can take over without admin intervention). Regards Markus Wanner -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
