Re: Support for N synchronous standby servers - take 2

On Wed, Feb 3, 2016 at 7:33 AM, Robert Haas wrote:
> Also, to be frank, I think we ought to be putting more effort into
> another patch in this same area, specifically Thomas Munro's causal
> reads patch. I think a lot of people today are trying to use
> synchronous replication to build load-balancing clusters and avoid the
> problem where you write some data and then read back stale data from a
> standby server. Of course, our current synchronous replication
> facilities make no such guarantees - his patch does, and I think
> that's pretty important. I'm not saying that we shouldn't do this
> too, of course.

Yeah, sure. Each one of those patches is trying to solve a different
problem where Postgres is deficient, here we'd like to be sure a
commit WAL record is correctly flushed on multiple standbys, while the
patch of Thomas is trying to ensure that there is no need to scan for
the replay position of a standby using some GUC parameters and a
validation/sanity layer in syncrep.c to do that. Surely the patch of
this thread has got more attention than Thomas', and both of them have
merits and try to address real problems. FWIW, the patch of Thomas is
a topic that I find rather interesting, and I am planning to look at
it as well, perhaps for next CF or even before that. We'll see how
other things move on.
--
Michael