On Mon, Aug 14, 2006 at 11:41:29PM +0300, Hannu Krosing wrote: > ??hel kenal p??eval, E, 2006-08-14 kell 18:21, kirjutas Peter Eisentraut: > > Perez wrote: > > > I thought, from watching the list for a while, that the planner > > > statistics needed were known but that how to gather the statistics > > > was not? > > > > I think over the course of the discussion we have figured out that we > > would like to have cross-column correlation statistics. The precise > > mathematical incarnation hasn't been determined yet, as far as I can > > see. Collecting the statistics thereafter isn't that hard, but there > > needs to be a way to not collect an exponential volume of statistics on > > all column combinations. > > I understood that the proposal was to collect only the stats where > needed (determined by user/dba) and use some rule-of-thumb values if no > collected stats were available.
Yeah, unless someone comes up with some kind of 'magic', I think trying to handle every cross-column possibility is a non-starter. IIRC, that argument is what's stalled cross-column stats every time in the past. It makes a lot more sense to allow defining what combinations of columns we need stats for. After that's done, it'd be easy to then write a script that will tell the database to collect stats on all multi-column indexes, RI, etc. Down the road, the planner could even be made to log (in a machine-readable format) every time it needs cross-column stats, and that data could be used to add stats that are needed. -- Jim C. Nasby, Sr. Engineering Consultant [EMAIL PROTECTED] Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461 ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
