Re: The documentation for READ COMMITTED may be incomplete or wrong

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 <tgl@sss.pgh.pa.us>
> 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