Horton

Re: To what extent should tests rely on VACUUM ANALYZE?

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Alexander Lakhin <exclusion@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, Alexander Korotkov <a.korotkov@postgrespro.ru>, Thomas Munro <thomas.munro@gmail.com>
Date: 2024-03-28T17:33:30Z
Lists: pgsql-hackers 
Tomas Vondra <tomas.vondra@enterprisedb.com> writes:
> Yeah. I think it's good to design the data/queries in such a way that
> the behavior does not flip due to minor noise like in this case.

+1

> But I'm a bit confused - how come the estimates do change at all? The
> analyze simply fetches 30k rows, and tenk only has 10k of them. So we
> should have *exact* numbers, and it should be exactly the same for all
> the analyze runs. So how come it changes like this?

It's plausible that the VACUUM ANALYZE done by test_setup fails
ConditionalLockBufferForCleanup() sometimes because of concurrent
activity like checkpointer writes.  I'm not quite sure how we
get from that to the observed symptom though.  Maybe the
VACUUM needs DISABLE_PAGE_SKIPPING?

			regards, tom lane

Commits

  1. Try to stabilize flappy test result.