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ed1a88ddamade it so WindowClauses can be merged when all window functions belonging to the WindowClause can equally well use some other WindowClause without any behavioral changes. When that optimization applies, the WindowFunc's "winref" gets adjusted to reference the new WindowClause. That commit does not work well with the deduplication logic in find_window_functions(), which only added the WindowFunc to the list when there wasn't already an identical WindowFunc in the list. That deduplication logic meant that the duplicate WindowFunc wouldn't get the "winref" changed when optimize_window_clauses() was able to swap the WindowFunc to another WindowClause. This could lead to the following error in the unlikely event that the deduplication code did something and the duplicate WindowFunc happened to be moved into another WindowClause. ERROR: WindowFunc with winref 2 assigned to WindowAgg with winref 1 As it turns out, the deduplication logic in find_window_functions() is pretty bogus. It might have done something when added, as that code predatesb8d7f053c, which changed how projections work. As it turns out, at least now we *will* evaluate the duplicate WindowFuncs. All that the deduplication code seems to do today is assist in underestimating the WindowAggPath costs due to not counting the evaluation costs of duplicate WindowFuncs. Ideally the fix would be to remove the deduplication code, but that could result in changes to the plan costs, as duplicate WindowFuncs would then be costed. Instead, let's play it safe and shift the deduplication code so it runs after the other processing in optimize_window_clauses(). Backpatch only as far as v16 as there doesn't seem to be any other harm done by the WindowFunc deduplication code before then. This issue was fixed in master by7027dd499. Reported-by: Meng Zhang <mza117jc@gmail.com> Author: Meng Zhang <mza117jc@gmail.com> Author: David Rowley <dgrowleyml@gmail.com> Discussion: https://postgr.es/m/CAErYLFAuxmW0UVdgrz7iiuNrxGQnFK_OP9hBD5CUzRgjrVrz=Q@mail.gmail.com Backpatch-through: 16
PostgreSQL Database Management System
This directory contains the source code distribution of the PostgreSQL database management system.
PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.
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