On Mon, 2007-09-24 at 16:04 +0200, Csaba Nagy wrote: > On Mon, 2007-09-24 at 14:27 +0100, Simon Riggs wrote: > > Csaba, please can you copy that data into fresh tables, re-ANALYZE and > > then re-post the EXPLAINs, with stats data. > > Well, I can of course. I actually tried to generate some random data > with similar record count and relations between the tables (which I'm > not sure I succeeded at), without the extra columns, but it was happily > yielding the nested loop plan. So I guess I really have to copy the > whole data (several tens of GB). > > But from my very limited understanding of what information is available > for the planner, I thought that the record count estimated for the join > between table_a and table_b1 on column b should be something like > > (estimated record count in table_a for value "a") * (weight of "b" range > covered by table_b1 and table_a in common) / (weight of "b" range > covered by table_a) There's no such code I'm aware of. Sounds a good idea though. I'm sure we could do something with the histogram values, but we don't in the default selectivity functions. -- Simon Riggs 2ndQuadrant http://www.2ndQuadrant.com ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
