We just fixed this - I'll post a patch, but I don't have time to verify against HEAD. - Luke On 8/24/07 3:38 AM, "Heikki Linnakangas" <heikki@xxxxxxxxxxxxxxxx> wrote: > Anton wrote: >>>> =# explain SELECT * FROM n_traf ORDER BY date_time DESC LIMIT 1; >>>> QUERY PLAN >>> ---------------------------------------------------------------------------- >>> ----------------------------- >>>> Limit (cost=824637.69..824637.69 rows=1 width=32) >>>> -> Sort (cost=824637.69..838746.44 rows=5643499 width=32) >>>> Sort Key: public.n_traf.date_time >>>> -> Result (cost=0.00..100877.99 rows=5643499 width=32) >>>> -> Append (cost= 0.00..100877.99 rows=5643499 width=32) >>>> -> Seq Scan on n_traf (cost=0.00..22.30 >>>> rows=1230 width=32) >>>> -> Seq Scan on n_traf_y2007m01 n_traf >>>> (cost=0.00..22.30 rows=1230 width=32) >> ... >>>> -> Seq Scan on n_traf_y2007m12 n_traf >>>> (cost=0.00..22.30 rows=1230 width=32) >>>> (18 rows) >>>> >>>> Why it no uses indexes at all? >>>> ------------------------------------------- >>> I'm no expert but I'd guess that the the planner doesn't know which >>> partition holds the latest time so it has to read them all. >> >> Agree. But why it not uses indexes when it reading them? > > The planner isn't smart enough to push the "ORDER BY ... LIMIT ..." > below the append node. Therefore it needs to fetch all rows from all the > tables, and the fastest way to do that is a seq scan. ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org