Horton

Violation of principle that plan trees are read-only

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-hackers@lists.postgresql.org
Cc: Andres Freund <andres@anarazel.de>
Date: 2025-05-18T23:31:33Z
Lists: pgsql-hackers

Commits

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  1. In ExecInitModifyTable, don't scribble on the source plan.

  2. Rely on executor utils to build targetlist for DML RETURNING.

While chasing down Valgrind leakage reports, I was disturbed
to realize that some of them arise from a case where the
executor scribbles on the plan tree it's given, which it is
absolutely not supposed to do:

        /*
         * Initialize result tuple slot and assign its rowtype using the first
         * RETURNING list.  We assume the rest will look the same.
         */
        mtstate->ps.plan->targetlist = (List *) linitial(returningLists);

A bit of git archaeology fingers Andres' commit 4717fdb14, which we
can't easily revert since he later got rid of ExecAssignResultType
altogether.  But I think we need to do something about it --- it's
purest luck that this doesn't cause serious problems in some cases.

			regards, tom lane