Re: write ahead logging in standby (streaming replication)

Hi,

Greg Stark wrote:
> I think my definition would be that a query against the replica will
> produce the same result as a query against the master -- and that that
> will be the case even after a system failure. That might not
> necessarily mean that the log entry is fsynced on the replica, only
> that it's fsynced in a location where the replica will have access to
> it when it runs recovery.

I tend to agree with that definition of synchrony for replicated
databases. However, let me point to an earlier thread around the same
topic:
http://archives.postgresql.org/message-id/4942ECF7.5040601@bluegap.ch

You will definitely find different definitions and requirements of what
synchronous replication means there. It convinced me that "synchronous"
is more of a marketing term in this area and is better avoided in
technical documents and discussions, or needs explanation.

As far as marketing goes, there are the customers who absolutely want
synchronous replication for its consistency and then there are the
others who absolutely don't want it due to its unusably high latency.

Regards

Markus Wanner