[ sorry for slow response, but I'd not gotten time to think about this... ] Sam Ross <elliptic@xxxxxxxxx> writes: > I was wondering why it seems that the query planner can't "see", based > on the histograms, that two join-columns have a very small > intersection, and adjust its row estimation accordingly. The reason why not is that eqjoinsel() doesn't take any such consideration into account. It's possible that it'd be a good idea to teach it to do so. I'm not entirely convinced though. It would add a fair amount of expense to that function, as well as adding some possibly shaky assumptions, and I'm not sure how often we'd get a usefully-better estimate in practice. OTOH, there are a lot of shaky assumptions in eqjoinsel() already, and we did decide this was worth worrying about in mergejoin cost estimation. Do you want to try it and submit a patch for testing? regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
