The cost_subqueryscan function does not judge whether it is parallel. regress -- Incremental sort vs. set operations with varno 0 set enable_hashagg to off; explain (costs off) select * from t union select * from t order by 1,3; QUERY PLAN ---------------------------------------------------------- Incremental Sort Sort Key: t.a, t.c Presorted Key: t.a -> Unique -> Sort Sort Key: t.a, t.b, t.c -> Append -> Gather Workers Planned: 2 -> Parallel Seq Scan on t -> Gather Workers Planned: 2 -> Parallel Seq Scan on t t_1 to Incremental Sort Sort Key: t.a, t.c Presorted Key: t.a -> Unique -> Sort Sort Key: t.a, t.b, t.c -> Gather Workers Planned: 2 -> Parallel Append -> Parallel Seq Scan on t -> Parallel Seq Scan on t t_1 Obviously the latter is less expensive
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fix-cost_subqueryscan-get-wrong-parallel-cost.patch
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