Re: Add pg_stat_autovacuum_priority

From: Nathan Bossart <nathandbossart(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Alexander Lakhin <exclusion(at)gmail(dot)com>, Sami Imseih <samimseih(at)gmail(dot)com>, Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>, Robert Treat <rob(at)xzilla(dot)net>, satyanarlapuram(at)gmail(dot)com, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, tndrwang(at)gmail(dot)com
Subject: Re: Add pg_stat_autovacuum_priority
Date: 2026-04-08 17:56:09
Message-ID: adaWuTR7oCKodH7k@nathan
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On Wed, Apr 08, 2026 at 01:17:45PM -0400, Tom Lane wrote:
> Alexander Lakhin <exclusion(at)gmail(dot)com> writes:
>> Please look at a new anomaly, I and SQLsmith have discovered:
>> SELECT (SELECT score FROM pg_stat_get_autovacuum_scores() LIMIT 1),
>>     (SELECT score FROM pg_stat_get_autovacuum_scores() LIMIT 1);
>> ERROR:  detected double pfree in PgStat Snapshot 0x5f6fa4d95d50
>
> Good catch, but you're not the first:
>
> https://www.postgresql.org/message-id/CAHewXNkJKdwb3D5OnksrdOqzqUnXUEMpDam1TPW0vfUkW%3D7jUw%40mail.gmail.com

Hm. I can't get excited about checking pgstat_fetch_consistency (as
proposed in that other report), but I see that commit 02502c1bca added the
freeing behavior in question. I wonder if it makes sense to just skip
freeing when relation_needs_vacanalyze() is called from the view, i.e., not
an autovacuum worker. On the other hand, maybe we shouldn't be caching
entries for a view like this that looks through all tables in the
database...

--
nathan

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