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2cb9ec1bcb
Commit c03ad5602f529787968fa3201b35c119bbc6d782 introduced a planner performance regression for UPDATE/DELETE on large inheritance sets. It required copying the append_rel_list (which is of size proportional to the number of inherited tables) once for each inherited table, thus resulting in O(N^2) time and memory consumption. While it's difficult to avoid that in general, the extra work only has to be done for append_rel_list entries that actually reference subquery RTEs, which inheritance-set entries will not. So we can buy back essentially all of the loss in cases without subqueries in FROM; and even for those, the added work is mainly proportional to the number of UNION ALL subqueries. Back-patch to 9.2, like the previous commit. Tom Lane and Dean Rasheed, per a complaint from Thomas Munro.