From: Japin Li <japinli@hotmail.com>
To: Dean Rasheed <dean.a.rasheed@gmail.com>
Cc: Kirk Wolak <wolakk@gmail.com>,  Pavel Stehule <pavel.stehule@gmail.com>,
  Andrew Dunstan <andrew@dunslane.net>,  PostgreSQL Hackers
 <pgsql-hackers@lists.postgresql.org>
Subject: Re: Global temporary tables
In-Reply-To: 
 <CAEZATCXYqx_aiDHWn9qUB8QGjE=dMzUEt_9WKjyHvDQFFf0U4w@mail.gmail.com>
	(Dean Rasheed's message of "Mon, 6 Jul 2026 11:12:32 +0100")
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Precedence: bulk

On Mon, 06 Jul 2026 at 11:12, Dean Rasheed <dean.a.rasheed@gmail.com> wrote=
:
> On Mon, 6 Jul 2026 at 09:35, Japin Li <japinli@hotmail.com> wrote:
>>
>> During testing of the v6 patch, I observed that sequences belonging to g=
lobal
>> temporary tables defined with ON COMMIT DELETE ROWS are not reset after =
the
>> transaction commits.
>>
>>     postgres=3D# BEGIN;
>>     postgres=3D*# INSERT INTO gtt_delete (info) VALUES ('row 1');
>>     postgres=3D*# SELECT * FROM gtt_delete;
>>     postgres=3D*# SELECT currval('gtt_delete_id_seq');
>>     postgres=3D*# END;
>>     postgres=3D# SELECT currval('gtt_delete_id_seq');  -- The sequence s=
till exists.
>>      currval
>>     ---------
>>            1
>>     (1 row)
>>     postgres=3D*# END;
>>     COMMIT
>>     postgres=3D# SELECT currval('gtt_delete_id_seq');  -- The sequence d=
oesn't reset.
>>      currval
>>     ---------
>>            2
>>     (1 row)
>>
>> The sequence doesn't reset after commit =E2=80=93 is this intended?
>>
>
> I think that's what I would expect. This matches what happens with
> normal (local) temp tables -- sequences are not reset after commit (or
> rollback, for that matter).
>

Thanks for the explanation!  I hadn't noticed this before.

> Regarding pg_class.reloncommit, 'p' (preserve) seems correct for a
> sequence attached to a GTT with ON COMMIT DELETE ROWS, because the
> sequence data is preserved. For indexes, not so much, because the
> index data is deleted on commit. I guess it could be NULL for anything
> that's not a table.
>

+1 for setting it to NULL for non=E2=80=91table objects, since CREATE INDEX=
 and
CREATE SEQUENCE do not support the ON COMMIT clause.

> Andrew's patch uses a reloption to store the table's on-commit state,
> but to me that doesn't seem quite right, and it requires special code
> to mark it as a "private" reloption that is non-user-editable. It does
> simplify the question of what to do for non-tables though. What do
> others think?
>

I'm on board with your approach to the on-commit state.

> Regards,
> Dean

--=20
Regards,
Japin Li
ChengDu WenWu Information Technology Co., Ltd.