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From: David Rowley <[email protected]>
To: Andrei Lepikhov <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Tom Lane <[email protected]>
Cc: a.rybakina <[email protected]>
Subject: Re: A very quick observation of dangling pointers in Postgres pathlists
Date: Tue, 21 Apr 2026 22:45:10 +1200
Message-ID: <CAApHDvrtG3KLZYvGc-u+w2nvJVjVD5YfZ3YKY9Fc+zSGXX0Y4w@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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On Tue, 21 Apr 2026 at 20:54, Andrei Lepikhov <[email protected]> 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.
>
> It would be great to have a copy_path() function. At the moment, I create a
> limited version each time in an extension module, using
> reparameterize_path_by_child as a guide since it ensures the core can handle
> path copies.
> Do you mean we can introduce such a copy routine to fix current issue? Here is
> the problem: dangling pointers are detected only by external tools. I can't
> imagine an SQL reproducer to test this machinery.

I had anticipated that we'd only fix in master as we'd probably need a
new callback in CustomPathMethods.

David

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