Robert Haas <robertmhaas@xxxxxxxxx> writes: > The reason I thought cross-column correlations might be relevant is > that the bitmap index scan on news_visible_from is quite accurate > (19976 estimated vs. 19932 actual) and the bitmap index scan on > news_visible_to is tolerably accurate (151 estimated vs. 41 actual) > but the estimate on the BitmapOr is somehow totally wrong (20127 > estimated vs. 0 actual). But on further reflection that doesn't make > much sense. How can the BitmapOr produce fewer rows than the sum of > its constituent inputs? That's not an estimation bug, that's a measurement bug. We don't try to count the actual number of rows present in the result of a BitmapOr or BitmapAnd node. (It would be impractical in lossy cases anyway, not to mention expensive.) regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
