Date: Sun, 24 Jan 2021 13:01:33 -0300
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Julien Rouhaud <rjuju123@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Faulty HEAP_XMAX_LOCK_ONLY & HEAP_KEYS_UPDATED hintbit
 combination
Message-ID: <20210124160133.GA32557@alvherre.pgsql>
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On 2021-Jan-24, Julien Rouhaud wrote:

> +	/*
> +	 * Do not allow tuples with invalid combinations of hint bits to be placed
> +	 * on a page.  These combinations are detected as corruption by the
> +	 * contrib/amcheck logic, so if you disable one or both of these
> +	 * assertions, make corresponding changes there.
> +	 */
> +	Assert(!((tuple->t_data->t_infomask & HEAP_XMAX_LOCK_ONLY) &&
> +			 (tuple->t_data->t_infomask2 & HEAP_KEYS_UPDATED)));
> 
> 
> I attach a simple self contained script to reproduce the problem, the last
> UPDATE triggering the Assert.
> 
> I'm not really familiar with this part of the code, so it's not exactly clear
> to me if some logic is missing in compute_new_xmax_infomask() /
> heap_prepare_insert(), or if this should actually be an allowed combination of
> hint bit.

Hmm, it's probably a bug in compute_new_xmax_infomask.  I don't think
the combination is sensible.

-- 
Álvaro Herrera                            39°49'30"S 73°17'W
"There is evil in the world. There are dark, awful things. Occasionally, we get
a glimpse of them. But there are dark corners; horrors almost impossible to
imagine... even in our worst nightmares." (Van Helsing, Dracula A.D. 1972)