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Re: Rework the way multixact truncations work

From: Noah Misch <noah(at)leadboat(dot)com>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>,"pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Rework the way multixact truncations work
Date: 2015-10-29 06:59:03
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Lists: pgsql-hackers
On Tue, Oct 27, 2015 at 03:44:10PM +0100, Andres Freund wrote:
> On 2015-10-24 22:07:00 -0400, Noah Misch wrote:
> > On Tue, Sep 22, 2015 at 07:57:27PM +0200, Andres Freund wrote:
> > > On 2015-09-22 13:38:58 -0400, Robert Haas wrote:
> > > > - If SlruDeleteSegment fails in unlink(), shouldn't we at the very
> > > > least log a message?  If that file is still there when we loop back
> > > > around, it's going to cause a failure, I think.
> > > 
> > > The existing unlink() call doesn't, that's the only reason I didn't add
> > > a message there. I'm fine with adding a (LOG or WARNING?) message.
> Note that I didn't add the warning after all, as it'd be too noisy
> during repeated replay, as all the files would already be gone. We could
> only emit it when the error is not ENOFILE, if people prefer that.
> > Unlinking old pg_clog files is strictly an optimization.  If you were to
> > comment out every unlink() call in slru.c, the only ill effect on CLOG is the
> > waste of disk space.  Is the same true of MultiXact?
> Well, multixacts are a lot larger than the other SLRUs, I think that
> makes some sort of difference.

That helps; thanks.  Your design seems good.  I've located only insipid
defects.  I propose to save some time by writing a patch series eliminating
them, which you could hopefully review.  Does that sound good?

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