I wrote: > I'm not sure if the costing change is a bug or not --- the non-bitmap scan > does seem to be cheaper in reality, but not by a couple orders of > magnitude as the planner now thinks.
Ah, scratch that, I wasn't looking closely enough. The 9.4 plan is an IndexScan whereas 9.5+ uses IndexOnlyScan, which accounts for the cost differential. The reason it changed is the remove_unused_subquery_outputs patch (55d5b3c08279b487), which allows the subquery to know that it doesn't actually have to return all columns of tenk1, so that an index-only scan is legal. regards, tom lane -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers