Re: Faulty HEAP_XMAX_LOCK_ONLY & HEAP_KEYS_UPDATED hintbit combination

From: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
To: Julien Rouhaud <rjuju123(at)gmail(dot)com>
Cc: Mahendra Singh Thalor <mahi6run(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Faulty HEAP_XMAX_LOCK_ONLY & HEAP_KEYS_UPDATED hintbit combination
Date: 2021-02-04 17:36:37
Message-ID: 20210204173637.GA30985@alvherre.pgsql
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On 2021-Feb-05, Julien Rouhaud wrote:

> Thanks, that's way better, copied in v3. I'm still a bit worried about that
> description though, as that flag isn't consistently set for the FOR UPDATE
> case. Well, to be more precise it's maybe consistently set when the hint bits
> are computed, but in some cases the flag is later cleared, so you won't
> reliably find it in the tuple.

Hmm, that sounds bogus. I think the resetting of the other bits should
be undone afterwards, but I'm not sure that we correctly set
KEYS_UPDATED again after the TOAST business. (What stuff does, from
memory, is to make the tuple look as if it is fully updated, which is
necessary during the TOAST handling; if the bits are not correctly set
transiently, that's okay. But it needs reinstated again later, once the
TOAST stuff is finished).

--
Álvaro Herrera 39°49'30"S 73°17'W
"El número de instalaciones de UNIX se ha elevado a 10,
y se espera que este número aumente" (UPM, 1972)

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