On Mon, 7 Apr 2008 19:42:02 +0200 Alban Hertroys <dalroi@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > explain analyze select distinct datestamp from vals; > > QUERY > > PLAN > > ---------------------------------------------------------------------- > > ------------------------------------------------------------------- > > Unique (cost=15003047.47..15380004.83 rows=4263 width=4) (actual > > time=649599.159..721671.595 rows=4252 loops=1) > > -> Sort (cost=15003047.47..15191526.15 rows=75391472 width=4) > > (actual time=649599.157..694392.602 rows=75391476 loops=1) > > Sort Key: datestamp > > Sort Method: external merge Disk: 1178592kB > > -> Seq Scan on vals (cost=0.00..1531261.72 rows=75391472 > > width=4) (actual time=9.104..93130.468 rows=75391476 loops=1) > > Total runtime: 722379.434 ms > > Wow, great estimates! The planner obviously knows how your data is > structured. So much for the bad planner estimation scenario... > > I haven't seen this "external merge Disk"-sort method before, maybe > it's new in 8.3, but it doesn't look promising for query I have to double check but I think that means he overflowed his work mem and is sorting on disk. Try increasing workmem for the query. Joshua D. Drake -- The PostgreSQL Company since 1997: http://www.commandprompt.com/ PostgreSQL Community Conference: http://www.postgresqlconference.org/ United States PostgreSQL Association: http://www.postgresql.us/ Donate to the PostgreSQL Project: http://www.postgresql.org/about/donate
