Feedback-ID: i0fe9450f:Fastmail
Date: Tue, 5 Mar 2024 12:13:08 +0900
From: Michael Paquier <michael@paquier.xyz>
To: feichanghong <feichanghong@qq.com>
Cc: pgsql-bugs <pgsql-bugs@lists.postgresql.org>,
	alvherre <alvherre@alvh.no-ip.org>
Subject: Re: BUG #18371: There are wrong constraint residues when detach hash
 partiton concurrently
Message-ID: <ZeaNxNW4m2106fSk@paquier.xyz>
References: <18371-7fef49f63de13f02@postgresql.org>
 <tencent_4DA59E77900C87CEBA0F0213000E64040D07@qq.com>
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On Thu, Feb 29, 2024 at 02:21:58PM +0800, feichanghong wrote:
> What I said here is wrong, the constraints on the hash partition will als=
o take
> effect. But this constraint depends on the oid of the parent partition.

Something is weird with the format of the messages you have sent, by
the way.=20

> Based on the analysis above, should the added constraint for a hash parti=
tion
> be dropped after detachment?I have initially implemented this logic
> in the attached patch and added a testcase. I really hope that
> developers can give me some suggestions.

I am not much a fan of relying on ATExecDropConstraint(), where the
logic introduced is a copy-paste of get_constraint_name() to retrieve
the name of the constraint to drop.  If any, we ought to rely more on
dropconstraint_internal() instead using the pg_constraint tuple based
on the OID of the constraint, and not do a cross-operation with the
constraint name.

But actually, why do you do a drop of the constraint at all?
DetachAddConstraintIfNeeded() re-adds the constraint as it is, so
instead of re-adding it as-is and then dropping it again, wouldn't it
be better to just *not* re-add to begin with it if we don't need it at
all?

This reproduces down to 14, for what I am assuming is an issue
introduced around 7b357cc6ae55.  Alvaro, what do you think?
--
Michael

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