Re: Turning off HOT/Cleanup sometimes

On 27 September 2014 09:29, Andres Freund <andres(at)anarazel(dot)de> wrote:
> On 2014-09-27 10:23:33 +0300, Heikki Linnakangas wrote:
>> This patch has gotten a fair amount of review, and has been rewritten once
>> during the commitfest. I think it's pretty close to being committable, the
>> only remaining question seems to be what to do with system catalogs. I'm
>> marking this as "Returned with feedback", I take it that Simon can proceed
>> from here, outside the commitfest.
>
> FWIW, I don't think it is, even with that. As is it seems very likely
> that it's going to regress a fair share of workloads. At the very least
> it needs a fair amount of benchmarking beforehand.

There is some doubt there. We've not seen a workload that does
actually exhibit a negative behaviour. I'm not saying one doesn't
exist, but it does matter how common/likely it is. If anyone can
present a performance test case that demonstrates a regression, I
think it will make it easier to discuss how wide that case is and what
we should do about it. Discussing whether to do various kinds of
limited pruning are moot until that is clear.

My memory was that it took months for people to understand the
frequent update use case, since catching it in flagrante delicto was
hard. That may be the case here, or not, but negative-benefit
experimental results very welcome.

Updated patch attached to address earlier comments.

--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services