Horton

Re: memory leak in trigger handling (since PG12)

Tom Lane <tgl@sss.pgh.pa.us>

View thread View on postgr.es
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-05-23T16:39:40Z
Lists: pgsql-hackers 
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

Commits

  1. Fix oversight in handling of modifiedCols since f24523672d

  2. Use per-tuple context in ExecGetAllUpdatedCols

  3. Generated columns