Heikki's got a point here: the planner is aware that hashjoin doesn't like skewed distributions, and it assigns extra cost accordingly if it can determine that the join key is skewed. (See the "bucketsize" stuff in cost_hashjoin.) If this patch is accepted we'll want to tweak that code.
Still, that has little to do with the current gating issue, which is whether we've convinced ourselves that the patch doesn't cause a performance decrease for cases in which it's unable to help. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers