Horton

Re: memory leak in trigger handling (since PG12)

Tomas Vondra <tomas.vondra@enterprisedb.com>

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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-05-23T20:57:31Z
Lists: pgsql-hackers 

On 5/23/23 18:39, Tom Lane wrote:
> 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 don't disagree, but which memory context should this use and
when/where should we switch to it?

I haven't seen any obvious memory context candidate in the code calling
ExecGetAllUpdatedCols, so I guess we'd have to pass it from above. Is
that a good idea for backbranches ...

regards

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

  1. Fix oversight in handling of modifiedCols since f24523672d

  2. Use per-tuple context in ExecGetAllUpdatedCols

  3. Generated columns