Re: Uh, I change my mind about commit_delay + commit_siblings (sort of)

On 31 May 2012 13:16, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, May 31, 2012 at 6:19 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> I've looked at this more closely now and I can see that the call to
>> XLogFlush() that is made from xact_redo_commit_internal() doesn't ever
>> actually flush WAL, so whether we delay or not is completely
>> irrelevant.
>>
>> So un-agreed. No change required to patch there.
>
> I think Peter's suggestion of forcibly setting the delay to 0 in the
> startup process is a good one, though.  It's one line of code, and if
> it isn't strictly necessary today, it still seems like good
> future-proofing.

Adding a line that does nothing is not a good idea. The Startup
process flushes very, very few WAL messages, so the setting is
irrelevant.

> I am not very happy about the idea of renaming commit_* to
> group_commit_*.  It's basically a cosmetic renaming, and breaking
> existing configuration files for cosmetic purposes does not seem
> warranted to me, especially when the old and new names are so close.
> I certainly don't think we can do that in 9.2, now that beta1 has
> already shipped.  Modifying the default contents of postgresql.conf
> after we've shipped beta has been a historical no-no for reasons that
> escape me at the moment, but IIRC they're not stupid reasons.
>
> Frankly, I think this whole thing should be pushed to 9.3.  The
> commit_delay and commit_siblings knobs suck, but they've sucked for a
> long time, and it won't kill anybody to wait another release cycle to
> fix them.  We have plenty of more important things queued up for 9.3
> already, and I don't believe there's any compelling reason to think
> that this particular thing needs preferential treatment.

No problem with pushing a variable rename through to 9.3. To be
honest, I don't care whether we rename them or not.

What matters is that we have a patch that provides a massive
performance gain in write performance in just a few lines of code, and
that should be committed to 9.2.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
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