Horton

Re: Latch for the WAL writer - further reducing idle wake-ups.

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Geoghegan <peter@2ndquadrant.com>
Cc: Magnus Hagander <magnus@hagander.net>, Robert Haas <robertmhaas@gmail.com>, PG Hackers <pgsql-hackers@postgresql.org>
Date: 2012-05-08T23:40:50Z
Lists: pgsql-hackers

Commits

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  1. Make bgwriter sleep longer when it has no work to do, to save electricity.

Peter Geoghegan <peter@2ndquadrant.com> writes:
> On 8 May 2012 22:35, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Now that I've actually read the patch, rather than just responding to
>> your description of it, I find myself entirely unhappy with the proposed
>> changes in the walwriter's sleep logic. You have introduced race
>> conditions (it is NOT okay to reset the latch somewhere below the top of
>> the loop)

> Yes, there is some checking of flags before the potential ResetLatch()
> call, which may be acted on. The code there is almost identical to
> that of the extant bgwriter code.

Um, yes, I noticed that shortly after sending my previous message.
I'm pretty unhappy about the current state of the bgwriter loop, too.
I rather wonder whether that coding explains the "postmaster failed to
shut down" errors that we've been seeing lately in the buildfarm.
Not noticing a shutdown signal promptly would go a long way towards
explaining that.

			regards, tom lane