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Re: A very quick observation of dangling pointers in Postgres pathlists

Andrei Lepikhov <lepihov@gmail.com>

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From: Andrei Lepikhov <lepihov@gmail.com>
To: David Rowley <dgrowleyml@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Tom Lane <tgl@sss.pgh.pa.us>
Date: 2026-04-29T12:43:02Z
Lists: pgsql-hackers

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On 27/04/2026 10:19, Andrei Lepikhov wrote:
> On 21/04/2026 10:35, David Rowley wrote:
>> IMO, we should write a function like copy_path() or reparent_path(),
>> which creates a copy of the given Path, or the latter also would copy
>> then set the ->parent to the given RelOptInfo.  Any time we use a path
>> directly from the pathlist of another RelOptInfo, we should reparent
>> or copy it. We could add an Assert in add_path() to check the new path
>> has the correct parent to help us find the places where we forget to
>> do this.
> 
> I've attached the patch so we can keep the discussion going.

While playing with random path choices [1], I found additional cases where a
path is assigned to two different RelOptInfos. See the attachment for a modified
patch.

[1] https://github.com/danolivo/pg-chaos-test

-- 
regards, Andrei Lepikhov,
pgEdge

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  1. Let Parallel Append over simple UNION ALL have partial subpaths.