Re: Core team statement on replication in PostgreSQL

On Fri, 2008-05-30 at 11:30 -0400, Andrew Dunstan wrote:
>
> Tom Lane wrote:
> > Simon Riggs <simon(at)2ndquadrant(dot)com> writes:
> >
> >> On Fri, 2008-05-30 at 12:31 +0530, Gurjeet Singh wrote:
> >>
> >>> On Fri, May 30, 2008 at 10:40 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >>>
> >>>> But since you mention it: one of the plausible answers for fixing the
> >>>> vacuum problem for read-only slaves is to have the slaves push an xmin
> >>>> back upstream to the master to prevent premature vacuuming.
> >>>>
> >>> I think it would be best to not make the slave interfere with the
> >>> master's operations; that's only going to increase the operational
> >>> complexity of such a solution.
> >>>
> >> We ruled that out as the-only-solution a while back. It does have the
> >> beauty of simplicity, so it may exist as an option or possibly the only
> >> way, for 8.4.
> >>
> > Yeah. The point is that it's fairly clear that we could make that work.
> > A solution that doesn't impact the master at all would be nicer, but
> > it's not at all clear to me that one is possible, unless we abandon
> > WAL-shipping as the base technology.
> >
> Quite. Before we start ruling things out let's know what we think we can
> actually do.

Let me re-phrase: I'm aware of that possibility and believe we can and
could do it for 8.4. My assessment is that people won't find it
sufficient and I am looking at other alternatives also. There may be a
better one possible for 8.4, there may not. Hence I've said "something
in 8.4, something better later". There is no need to decide that is the
only way forward, yet.

I hope and expect to put some of these ideas into a more concrete form,
but this has not yet happened. Nothing has slipped, not having any
trouble getting on with it, just that my plans were to not start it yet.
I think having a detailed design ready for review by September commit
fest is credible.

> I hope that NTT will release their code ASAP so we will have a better
> idea of what we have and what we need.

That has very little to do with Hot Standby, though there could be patch
conflicts, which is why I'm aiming to get WAL streaming done first.

--
Simon Riggs www.2ndQuadrant.com
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