Horton

Re: support for MERGE

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Jaime Casanova <jcasanov@systemguards.com.ec>
Cc: Simon Riggs <simon.riggs@enterprisedb.com>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Zhihong Yu <zyu@yugabyte.com>, Daniel Westermann <dwe@dbi-services.com>, Amit Langote <amitlangote09@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>, Pavan Deolasee <pavan.deolasee@gmail.com>
Date: 2022-01-20T21:02:43Z
Lists: pgsql-hackers 
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  —  https://www.EnterpriseDB.com/
Tom: There seems to be something broken here.
Teodor: I'm in sackcloth and ashes...  Fixed.
        http://archives.postgresql.org/message-id/482D1632.8010507@sigaev.ru

Commits

  1. Doc fixes for MERGE statement

  2. MERGE docs adjustments

  3. Link to MVCC docs in MERGE docs

  4. Fix EXPLAIN MERGE output when no tuples are processed

  5. Make EXPLAIN MERGE output format more compact

  6. Add support for MERGE SQL command

  7. Split ExecUpdate and ExecDelete into reusable pieces

  8. Add API of sorts for transition table handling in trigger.c

  9. Represent Lists as expansible arrays, not chains of cons-cells.