Re: protocol change in 7.4

Neil Conway wrote:
> Mike Mascari <mascarm(at)mascari(dot)com> writes:
>
>>Is there any thought about changing the protocol to support
>>two-phase commit? Not that 2PC and distributed transactions would be
>>implemented in 7.4, but to prevent another protocol change in the
>>future?
>
> My understanding is that 2PC is one way to implement multi-master
> replication. If that's what you're referring to, then I'm not sure I
> see the point: the multi-master replication project (pgreplication)
> doesn't use 2PC, due to apparent scalability problems (not to mention
> that it also uses a separate channel for communications between
> backends on different nodes).

Actually, I was thinking along the lines of a true CREATE
DATABASE LINK implementation, where multiple databases could
participate in a distributed transaction. That would require the
backend in which the main query is executing to act as the
"coordinator" and each of the other participating databases to
act as "cohorts". And would require a protocol change to support
the PREPARE, COMMIT-VOTE/ABORT-VOTE reply, and an ACK message
following the completion of the distributed COMMIT or ABORT.

Mike Mascari
mascarm(at)mascari(dot)com