| From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Greg Stark <stark(at)mit(dot)edu>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Simon Riggs <simon(dot)riggs(at)2ndquadrant(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Peter Eisentraut <peter_e(at)gmx(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com> |
| Subject: | Re: Turning off HOT/Cleanup sometimes |
| Date: | 2015-04-22 21:07:00 |
| Message-ID: | 20150422210659.GH4369@alvh.no-ip.org |
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| Lists: | pgsql-hackers |
Bruce Momjian wrote:
> On Wed, Apr 22, 2015 at 04:36:17PM +0100, Greg Stark wrote:
> > On Mon, Apr 20, 2015 at 8:48 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> > > Well, we have to assume there are many misconfigured configurations ---
> > > autovacuum isn't super-easy to configure, so we can't just blame the
> > > user if this makes things worse. In fact, page pruning was designed
> > > spefically for cases where autovacuum wasn't running our couldn't keep
> > > up.
> >
> > Well autovacuum isn't currently considering HOT pruning part of its
> > job at all. It's hard to call it "misconfigured" when there's
> > literally *no* way to configure it "correctly".
>
> Good point, but doesn't vacuum remove the need for pruning as it removes
> all the old rows?
Sure. The point, I think, is to make autovacuum runs of some sort that
don't actually vacuum but only do HOT-pruning. Maybe this is a
reasonable solution to the problem that queries don't prune anymore
after Simon's patch. If we made autovac HOT-prune periodically, we
could have read-only queries prune only already-dirty pages. Of course,
that would need further adjustments to default number of autovac
workers, I/O allocation, etc.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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