Add pg_partition_root to get top-most parent of a partition tree

From: Michael Paquier <michael(at)paquier(dot)xyz>
To: Postgres hackers <pgsql-hackers(at)postgresql(dot)org>
Cc: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Subject: Add pg_partition_root to get top-most parent of a partition tree
Date: 2018-12-07 01:40:15
Message-ID: 20181207014015.GP2407@paquier.xyz
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Hi all,

Álvaro has given faced a use case where it would be useful to have a
function which is able to return the top-most parent of a partition
tree:
https://postgr.es/m/20181204184159.eue3wlchqrkh4vsc@alvherre.pgsql

This has been mentioned as well on the thread where was discussed
pg_partition_tree, but it got shaved from the committed patch as many
things happened when discussing the thing.

Attached is a patch to do the work, which includes documentation and
tests. An argument could be made to include the top-most parent as part
of pg_partition_tree, but it feels more natural to me to have a separate
function. This makes sure to handle invalid relations by returning
NULL, and it generates an error for incorrect relkind.

I have included as well a fix for the recent crash on pg_partition_tree
I have reported, but let's discuss the crash on its thread here:
https://www.postgresql.org/message-id/20181207010406.GO2407@paquier.xyz
The bug fix would most likely get committed first, and I'll rebase this
patch as need be.

I am adding this patch to the CF of January. I think that Amit should
also be marked as a co-author of this patch, as that's inspired from
what has been submitted previously, still I have no reused the code.

Thanks,
--
Michael

Attachment Content-Type Size
partition-root-v1.patch text/x-diff 13.7 KB

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