On Thu, 2013-01-24 at 15:45 +0100, Alexander Farber wrote: > Hello - > > On Thu, Jan 24, 2013 at 3:39 PM, Alban Hertroys <haramrae@xxxxxxxxx> wrote: > > On 24 January 2013 10:57, Alexander Farber <alexander.farber@xxxxxxxxx> > > wrote: > >> > >> # explain analyze select count(id) from ( > >> select id, > >> row_number() over(partition by yw order by money > >> desc) as ranking > >> from pref_money > >> ) x > >> where x.ranking = 1 and id='OK452217781481'; > >> QUERY PLAN > >> > >> ------------------------------------------------------------------------------------------------------------------------------------------- > >> Aggregate (cost=63694.22..63694.23 rows=1 width=82) (actual > >> time=4520.719..4520.719 rows=1 loops=1) > >> -> Subquery Scan x (cost=48519.10..63694.19 rows=11 width=82) > >> (actual time=4470.620..4520.710 rows=6 loops=1) > >> Filter: ((x.ranking = 1) AND ((x.id)::text = > >> 'OK452217781481'::text)) > >> -> WindowAgg (cost=48519.10..57190.58 rows=433574 width=26) > >> (actual time=4293.315..4491.652 rows=429803 loops=1) > >> -> Sort (cost=48519.10..49603.03 rows=433574 > >> width=26) (actual time=4293.306..4352.544 rows=429803 loops=1) > >> Sort Key: pref_money.yw, pref_money.money > >> Sort Method: external sort Disk: 15856kB > > > > > > It's sorting on disk. That's not going to be fast. Indeed, it's taking > > nearly all the time the query takes (4.4s for this step out of 4.5s for the > > query). > > I've noticed that too, but what > does "sorting on disk" mean? > > I have a lot of RAM (32 GB) , > should I increase work_mem even more? > (it is currenlty 32 MB) > You should better create an index on pref_money(yw, money). It could help you get rid of the seqscan and sort operations. -- Guillaume http://blog.guillaume.lelarge.info http://www.dalibo.com -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
