Re: Add shared buffer hits to pg_stat_io

From: Andres Freund <andres(at)anarazel(dot)de>
To: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Cc: "Drouvot, Bertrand" <bertranddrouvot(dot)pg(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Maciek Sakrejda <m(dot)sakrejda(at)gmail(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, smilingsamay(at)gmail(dot)com, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, Lukas Fittl <lukas(at)fittl(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Subject: Re: Add shared buffer hits to pg_stat_io
Date: 2023-03-08 19:23:42
Message-ID: 20230308192342.fpbnsofdl2kxb23f@awork3.anarazel.de
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On 2023-03-08 13:44:32 -0500, Melanie Plageman wrote:
> However, I am concerned that, while unlikely, this could be flakey.
> Something could happen to force all of those blocks out of shared
> buffers (even though they were just read in) before we hit them.

You could make the test query a simple nested loop self-join, that'll prevent
the page being evicted, because it'll still be pinned on the outer side, while
generating hits on the inner side.

Greetings,

Andres Freund

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