On Thu, May 12, 2005 at 08:54:48PM +0200, Manfred Koizar wrote: > On Wed, 11 May 2005 16:15:16 -0500, "Jim C. Nasby" <[EMAIL PROTECTED]> > wrote: > >> This is divided by the number of index columns, so the index correlation > >> is estimated to be 0.219. > > > >That seems like a pretty bad assumption to make. > > Any assumption we make without looking at entire index tuples has to be > bad. A new GUC variable secondary_correlation introduced by my patch at > least gives you a chance to manually control the effects of additional > index columns.
It seems it would be much better to gather statistics on any multi-column indexes, but I know that's probably beyond what's reasonable for your patch. Also, my data (http://stats.distributed.net/~decibel) indicates that max_io isn't high enough. Look specifically at timing2.log compared to timing.log. Thouggh, it is possibile that this is because of having random_page_cost set to 1.1 (if I set it much higher I can't force the index scan because the index estimate actually exceeds the cost of the seqscan with the disable cost added in). > >It depends on the patches, since this is a production machine. Currently > >it's running 7.4.*mumble*, > > The patch referenced in > http://archives.postgresql.org/pgsql-hackers/2003-08/msg00931.php is > still available. It doesn't touch too many places and should be easy to > review. I'm using it and its predecessors in production for more than > two years. Let me know, if the 74b1 version does not apply cleanly to > your source tree. Looks reasonable; I'll give it a shot on 8.0 once I have replication happening. -- Jim C. Nasby, Database Consultant [EMAIL PROTECTED] Give your computer some brain candy! www.distributed.net Team #1828 Windows: "Where do you want to go today?" Linux: "Where do you want to go tomorrow?" FreeBSD: "Are you guys coming, or what?" ---------------------------(end of broadcast)--------------------------- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])