On Tue, May 09, 2006 at 09:24:15 +0530, soni de <soni.de@xxxxxxxxx> wrote: > > EXPLAIN > pdb=# EXPLAIN ANALYZE select * from wan where kname = 'pluto' order by stime > limit 50; > NOTICE: QUERY PLAN: > > Limit (cost=3515.32..3515.32 rows=50 width=95) (actual time= > 230492.69..230493.07 rows=50 loops=1) > -> Sort (cost=3515.32..3515.32 rows=208 width=95) (actual time= > 230492.68..230493.00 rows=51 loops=1) > -> Seq Scan on wan (cost=0.00..3507.32 rows=208 width=95) (actual > time=0.44..229217.38 rows=18306 loops=1) > Total runtime: 230631.62 msec Unless you have an index on (kname, stime) the query is going to need to find the records with a value for kname of 'pluto' and then get the most recent 50 of them. It looks like there are enough estimated records with kname = 'pluto', that a sequential scan is being prefered. Creating an extra index will slow down inserts somewhat, but will speed up queries like the above significantly, so may be worthwhile for you. I think later versions of Postgres are smarter, but for sure in 7.2 you will need to write the query like: SELECT * FROM wan WHERE kname = 'pluto' ORDER BY kname DESC, stime DESC LIMIT 50 ;
