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From: Nathan Bossart <[email protected]>
To: Tom Lane <[email protected]>
Cc: Aleksander Alekseev <[email protected]>
Cc: Amit Langote <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: The documentation for READ COMMITTED may be incomplete or wrong
Date: Thu, 18 May 2023 12:51:23 -0700
Message-ID: <20230518195123.GA3362715@nathanxps13> (raw)
In-Reply-To: <[email protected]>
References: <CAJ7c6TMBTN3rcz4=AjYhLPD_w3FFT0Wq_C15jxCDn8U4tZnH1g@mail.gmail.com>
	<[email protected]>
	<[email protected]>

On Thu, May 18, 2023 at 11:22:54AM -0400, Tom Lane wrote:
> Ugh.  Bisecting says it broke at
> 
> 86dc90056dfdbd9d1b891718d2e5614e3e432f35 is the first bad commit
> commit 86dc90056dfdbd9d1b891718d2e5614e3e432f35
> Author: Tom Lane <[email protected]>
> Date:   Wed Mar 31 11:52:34 2021 -0400
> 
>     Rework planning and execution of UPDATE and DELETE.
> 
> which was absolutely not supposed to be breaking any concurrent-execution
> guarantees.  I wonder what we got wrong.

With the reproduction steps listed upthread, I see that XMAX for both
tuples is set to the deleting transaction, but the one in inh_child_2 has
two additional infomask flags: HEAP_XMAX_EXCL_LOCK and HEAP_XMAX_LOCK_ONLY.
If I add a third table (i.e., inh_child_3), XMAX for all three tuples is
set to the deleting transaction, and only the one in inh_child_3 has the
lock bits set.  Also, in the three-table case, the DELETE statement reports
"DELETE 2".

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

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