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From: Andres Freund <[email protected]>
To: Tom Lane <[email protected]>
Cc: Nathan Bossart <[email protected]>
Cc: Alexander Lakhin <[email protected]>
Cc: Sami Imseih <[email protected]>
Cc: Bharath Rupireddy <[email protected]>
Cc: Robert Treat <[email protected]>
Cc: [email protected]
Cc: pgsql-hackers <[email protected]>
Cc: [email protected]
Subject: Re: Add pg_stat_autovacuum_priority
Date: Wed, 8 Apr 2026 16:40:03 -0400
Message-ID: <u3akkfw3vaocviudt6f7ft4kxjc2273rh3tfhz5rfwg6jrcc2t@wurwws6wgjjz> (raw)
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Hi,

On 2026-04-08 15:21:38 -0400, Tom Lane wrote:
> Hmm, yeah I suppose a caller that doesn't care about leakage could
> skip the pfree.  But are there really any of those?  The complaint
> that prompted 02502c1bc concerned databases with many many thousands
> of relations.

Most of the calls come from SQL callable functions that just return a value to
the user. For those I don't think we gain anything by doing retail pfrees, if
anything it'd hurt performance.


> I now realize that what you said upthread about caching the results
> might be a bigger problem, ie if the pgstats code does retain all
> these values then we'd have a memory bloat problem there.  Maybe
> we need a more aggressive API change that includes a way to specify
> "don't cache this result".

I can't stop myself from pointing out that the whole reason this caching stuff
exists is because you insistet that we provide an equivalent for snapshotting
semantics of the pre-shmem stats system...

Note that the whole cached state does automatically get reset at the end of
the transaction (AtEOXact_PgStat()->pgstat_clear_snapshot()), just like it did
before the shmem stats stuff.

Greetings,

Andres Freund

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