MIME-Version: 1.0
References: <adab9758-f346-4263-93af-3e37b7b315b7@gmail.com>
 <20be3d9d-4147-492a-b69c-d69a87a014a9@gmail.com>
 <CAApHDvpBZ_hj0p1fYYQCxk9eCfNSsjFfR+LYCEryek9Mxh1V0Q@mail.gmail.com>
 <1b67f95c-27a5-42dd-8c95-efe452094dc3@gmail.com>
In-Reply-To: <1b67f95c-27a5-42dd-8c95-efe452094dc3@gmail.com>
From: David Rowley <dgrowleyml@gmail.com>
Date: Tue, 21 Apr 2026 22:45:10 +1200
Message-ID: 
 <CAApHDvrtG3KLZYvGc-u+w2nvJVjVD5YfZ3YKY9Fc+zSGXX0Y4w@mail.gmail.com>
Subject: Re: A very quick observation of dangling pointers in Postgres
 pathlists
To: Andrei Lepikhov <lepihov@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
 Tom Lane <tgl@sss.pgh.pa.us>,
	"a.rybakina" <a.rybakina@postgrespro.ru>
Content-Type: text/plain; charset="UTF-8"
Archived-At: 
 <https://www.postgresql.org/message-id/CAApHDvrtG3KLZYvGc-u%2Bw2nvJVjVD5YfZ3YKY9Fc%2BzSGXX0Y4w%40mail.gmail.com>
Precedence: bulk

On Tue, 21 Apr 2026 at 20:54, Andrei Lepikhov <lepihov@gmail.com> 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