From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: memory leak in trigger handling (since PG12)
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Comments: In-reply-to Tomas Vondra <tomas.vondra@enterprisedb.com>
	message dated "Tue, 23 May 2023 18:23:00 +0200"
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Date: Tue, 23 May 2023 12:39:40 -0400
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Tomas Vondra <tomas.vondra@enterprisedb.com> writes:
> it seems there's a fairly annoying memory leak in trigger code,
> introduced by
> ...
> Attached is a patch, restoring the pre-12 behavior for me.

> While looking for other places allocating stuff in ExecutorState (for
> the UPDATE case) and leaving it there, I found two more cases:

> 1) copy_plpgsql_datums

> 2) make_expanded_record_from_tupdesc
>    make_expanded_record_from_exprecord

> All of this is calls from plpgsql_exec_trigger.

Not sure about the expanded-record case, but both of your other two
fixes feel like poor substitutes for pushing the memory into a
shorter-lived context.  In particular I'm quite surprised that
plpgsql isn't already allocating that workspace in the "procedure"
memory context.

> I wonder how much we should care about these cases. On the one hand we
> often leave the cleanup up to the memory context, but the assumption is
> the context is not unnecessarily long-lived. And ExecutorState is not
> that. And leaking memory per-row does not seem great either.

I agree per-row leaks in the ExecutorState context are not cool.

			regards, tom lane