Re: Configuring synchronous replication

> That said, the timeout option also feels a bit wishy-washy to me. With a
> timeout, acknowledgment of a commit means "your transaction is safely
> committed in the master and slave. Or not, if there was some glitch with
> the slave". That doesn't seem like a very useful guarantee; if you're
> happy with that why not just use async replication?

Ah, I wasn't clear.  My thought was that a standby which exceeds the
timeout would be marked as "nonresponsive" and no longer included in the
list of standbys which needed to be synchronized.  That is, the timeout
would be a timeout which says "this standby is down".

> So the only case where standby registration is required is where you
> deliberately choose to *not* have N+1 redundancy and then yet still
> require all N standbys to acknowledge. That is a suicidal config and
> nobody would sanely choose that. It's not a large or useful use case for
> standby reg. (But it does raise the question again of whether we need
> quorum commit).

Thinking of this as a sysadmin, what I want is to have *one place* I can
go an troubleshoot my standby setup.  If I have 12 synch standbys and
they're creating too much load on the master, and I want to change half
of them to async, I don't want to have to ssh into 6 different machines
to do so.  If one standby needs to be taken out of the network because
it's too slow, I want to be able to log in to the master and instantly
identify which standby is lagging and remove it there.

--                                  -- Josh Berkus                                    PostgreSQL Experts Inc.
                        http://www.pgexperts.com