Re: Non-deterministic buffer counts reported in execution with EXPLAIN ANALYZE BUFFERS

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Tomas Vondra <tomas(at)vondra(dot)me>
Cc: David Rowley <dgrowleyml(at)gmail(dot)com>, Radim Marek <radim(at)boringsql(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Non-deterministic buffer counts reported in execution with EXPLAIN ANALYZE BUFFERS
Date: 2026-02-05 15:25:25
Message-ID: 1613669.1770305125@sss.pgh.pa.us
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Tomas Vondra <tomas(at)vondra(dot)me> writes:
> On 2/5/26 01:15, David Rowley wrote:
>> I imagined if it's just for machines running tests then you could just
>> load everything. If it was coded in such a way that a tuple fetched by
>> doing a Seq Scan on the catalogue table was what went into the cache,
>> rather than the Seq Scan drives the normal cache lookup code,
>> resulting in a subsequent Index Scan on the catalogue's index, then it
>> could be done with fairly low overhead. I imagine in the order of
>> <10ms from fresh initdb. That doesn't seem excessively long for
>> machines running tests in the background.

> So we'd just go through all the caches relcaches/catcaches/... and load
> all the stuff that's in pg_catalog? I guess that could work,

... until there's a cache flush event. This whole discussion seems
to me to be based on a misconception.

regards, tom lane

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