| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> |
| Cc: | Alexander Lakhin <exclusion(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
| Subject: | Re: To what extent should tests rely on VACUUM ANALYZE? |
| Date: | 2024-03-28 17:33:30 |
| Message-ID: | 3640269.1711647210@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)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
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