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: 2021-02-23 20:47:33
Message-ID: 20210223204733.GA11420@alvherre.pgsql
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On 2021-Feb-05, Julien Rouhaud wrote:

> Thanks, that's way better, copied in v3.

Thank you, pushed. The code changes are only relevant in master, but I
did back-patch the README.tuplock to all live branches.

> 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.

Is that right? I think compute_new_xmax_infomask would set the bit to
infomask2_old_tuple (its last output argument) if it's needed, and so
the bit would find its way to infomask2 eventually. Do you have a case
where it doesn't achieve that?

Álvaro Herrera Valdivia, Chile
"E pur si muove" (Galileo Galilei)

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