Re: support for MERGE

From: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
To: Jaime Casanova <jcasanov(at)systemguards(dot)com(dot)ec>
Cc: Simon Riggs <simon(dot)riggs(at)enterprisedb(dot)com>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Zhihong Yu <zyu(at)yugabyte(dot)com>, Daniel Westermann <dwe(at)dbi-services(dot)com>, Amit Langote <amitlangote09(at)gmail(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Pg Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>
Subject: Re: support for MERGE
Date: 2022-01-20 21:02:43
Message-ID: 202201202102.5ta7rb3vyvkh@alvherre.pgsql
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On 2022-Jan-12, Jaime Casanova wrote:

> I found two crashes, actually I found them on the original patch Álvaro
> sent on november but just checked that those already exists.
> I configured with:
> CFLAGS="-ggdb -Og -g3 -fno-omit-frame-pointer" ./configure --prefix=/opt/var/pgdg/15/merge --enable-debug --enable-depend --enable-cassert --with-llvm --enable-tap-tests --with-pgport=54315
> And tested on the regression database.
> Attached the SQL files for the crashes and its respective stacktraces.
> FWIW, the second crash doesn't appear to be caused by the MERGE patch
> but I cannot trigger it other way.

Thanks for this! The problem in the first crash was that when
partitioned tables are being used and the topmost one has a tuple
descriptor different from the partitions, we were doing the projection
to the partition's slot using the root's tupledesc and a targetlist
written for the root. The reason this crashed in such ugly way is that
in this case the parent has 3 columns (2 dropped) while the partitions
only have one, so the projection was trying to write to an attribute
that didn't exist.

I fixed it by making all NOT MATCHED actions use the root table's
descriptor and slot.

This change fixes both your reported crashes. I didn't look closely to
see if the second one is caused by exactly the same issue.

Álvaro Herrera Valdivia, Chile —
Tom: There seems to be something broken here.
Teodor: I'm in sackcloth and ashes... Fixed.

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