Horton

Re: Speed up transaction completion faster after many relations are accessed in a transaction

Heikki Linnakangas <hlinnaka@iki.fi>

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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: David Rowley <dgrowleyml@gmail.com>
Cc: vignesh C <vignesh21@gmail.com>, Jacob Champion <jchampion@timescale.com>, Yura Sokolov <y.sokolov@postgrespro.ru>, Zhihong Yu <zyu@yugabyte.com>, Michael Paquier <michael@paquier.xyz>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, Tom Lane <tgl@sss.pgh.pa.us>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>, "Imai, Yoshikazu" <imai.yoshikazu@jp.fujitsu.com>, Andres Freund <andres@anarazel.de>, Simon Riggs <simon@2ndquadrant.com>, Amit Langote <amitlangote09@gmail.com>
Date: 2023-09-15T10:37:11Z
Lists: pgsql-hackers 
On 11/09/2023 15:00, David Rowley wrote:
> On Wed, 5 Jul 2023 at 21:44, Heikki Linnakangas <hlinnaka@iki.fi> wrote:
>>
>>> index 296dc82d2ee..edb8b6026e5 100644
>>> --- a/src/backend/commands/discard.c
>>> +++ b/src/backend/commands/discard.c
>>> @@ -71,7 +71,7 @@ DiscardAll(bool isTopLevel)
>>>          Async_UnlistenAll();
>>> -       LockReleaseAll(USER_LOCKMETHOD, true);
>>> +       LockReleaseSession(USER_LOCKMETHOD);
>>>          ResetPlanCache();
>>
>> This assumes that there are no transaction-level advisory locks. I think
>> that's OK. It took me a while to convince myself of that, though. I
>> think we need a high level comment somewhere that explains what
>> assumptions we make on which locks can be held in session mode and which
>> in transaction mode.
> 
> Isn't it ok because DISCARD ALL cannot run inside a transaction block,
> so there should be no locks taken apart from possibly session-level
> locks?

Hmm, sounds valid. I think I convinced myself that it's OK through some 
other reasoning, but I don't remember it now.

> I've added a call to LockAssertNoneHeld(false) in there.

I don't see it in the patch?

-- 
Heikki Linnakangas
Neon (https://neon.tech)

Commits

  1. Reorder LOCALLOCK structure members to compact the size

  2. Be more careful to not lose sync in the FE/BE protocol.