On Sun, Feb 28, 2010 at 3:19 PM, Josh Berkus <josh@xxxxxxxxxxxx> wrote: > All, > > I'm seeing in a production database two problems with query rowcount > estimation: > > (1) Estimates for the number of rows in an outer join do not take into > account any constraint exclusion (CE) in operation. > > (2) Row estimates do not take into account if the unique indexes on the > child partitions are different from the master partition (the append > node). This is often true, because the key to the master is ( key, ce > column) and for the children is just ( key ). > > The result is that if you do a series of outer joins using the CE > criterion against partitioned tables, the row estimates you get will be > several orders of magnitude too high ... and the subsequent query plan > far too pessimistic. > > Anyone else seeing this? Do any of the 9.0 patches address the above > issues? I feel like I've seen these way-too-high row estimates in some other postings to -performance, but I'm not sure if it was the same issue. You don't by chance have a RTC? I don't think it's likely fixed in 9.0 but it would be interesting to investigate. ...Robert -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
