Re: Turning off HOT/Cleanup sometimes

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Peter Eisentraut <peter_e(at)gmx(dot)net>
Cc: Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(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>, Greg Stark <stark(at)mit(dot)edu>, 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>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>
Subject: Re: Turning off HOT/Cleanup sometimes
Date: 2015-04-22 18:05:03
Message-ID: 20150422180503.GC13362@momjian.us
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On Tue, Apr 21, 2015 at 05:07:52PM -0400, Peter Eisentraut wrote:
> On 4/21/15 4:45 PM, Jim Nasby wrote:
> > This comment made me wonder... has anyone considered handing the pruning
> > work off to a bgworker, at least for SELECTs? That means the selects
> > themselves wouldn't be burdened by the actual prune work, only in
> > notifying the bgworker. While that's not going to be free, presumably
> > it's a lot cheaper...
>
> The nice thing about having foreground queries to the light cleanup is
> that they can work in parallel and naturally hit the interesting parts
> of the table first.
>
> In order for a background worker to keep up with some of the workloads
> that have been presented as counterexamples, you'd need multiple
> background workers operating in parallel and preferring to work on
> certain parts of a table. That would require a lot more sophisticated
> job management than we currently have for, say, autovacuum.

Well, the visibility map tells us where _not_ to clean up, so using
another map to tell use _where_ to cleanup might make sense. However,
the density of the map might be low enough that a list makes more sense,
as you suggested.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ Everyone has their own god. +

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