Re: Postgres: Queries are too slow after upgrading to PG17 from PG15

From: Peter Geoghegan <pg(at)bowt(dot)ie>
To: Sajith Prabhakar Shetty <ssajith(at)blackduck(dot)com>
Cc: Merlin Moncure <mmoncure(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andrei Lepikhov <lepihov(at)gmail(dot)com>, "pgsql-bugs(at)lists(dot)postgresql(dot)org" <pgsql-bugs(at)lists(dot)postgresql(dot)org>, Todd Cook <cookt(at)blackduck(dot)com>
Subject: Re: Postgres: Queries are too slow after upgrading to PG17 from PG15
Date: 2025-08-21 01:48:31
Message-ID: CAH2-WzmACH8cXhGG7gXj_S=nAAKMezrT7=9bUDyRoOo2sRA-4g@mail.gmail.com
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On Tue, Aug 12, 2025 at 12:46 AM Sajith Prabhakar Shetty
<ssajith(at)blackduck(dot)com> wrote:
> I can confirm with full certainty that both VACUUM and ANALYZE were executed on all three instances whose results I shared.

The results that you shared showed "Heap Fetches: 598,916" -- one heap
fetch per index search (for the problematic index scan).

Perhaps VACUUM ran without being truly effective, due to the removable
cutoff/horizon being held back by a long running query. Though that
generally won't happen on a quiescent system -- so it really does look
like VACUUM hasn't been run.

--
Peter Geoghegan

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