Re: Turning off HOT/Cleanup sometimes

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, Andres Freund <andres(at)anarazel(dot)de>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, 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>, 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: 2015-04-20 20:56:20
Message-ID: CANP8+j+L7XVVpsAnBkBykFq_c_g2mF-NA2X88OSrS9ov14S_Zg@mail.gmail.com
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On 20 April 2015 at 20:28, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:

> But why should 1 SELECT or 20 SELECTs or 200 SELECTs have to do a job,
> while the user waits, which is fundamentally VACUUM's duty to do in the
> background?
>

Agreed. I don't see a % as giving us anything at all.

The idea is that we want to turn an O(N) problem for one query into an O(1)
task.

> The use case I see for this is when there is a mixed workload. There is
> one select which reads the entire table, and hundreds of thousands of
> selects/updates/insert that don't, and of course vacuum comes along every
> now and then and does it thing. Why should the one massive SELECT have
> horrible performance just because it was run right before autovacuum would
> have kicked in instead of right after if finished?
>

+1

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

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