> On 03/23/2011 04:17 AM, Adarsh Sharma wrote: > >> explain analyze select distinct(p.crawled_page_id) from page_content >> p where NOT EXISTS (select 1 from clause2 c where c.source_id = >> p.crawled_page_id); > > You know... I'm surprised nobody has mentioned this, but DISTINCT is > very slow unless you have a fairly recent version of Postgres that > replaces it with something faster. Try this: Nobody mentioned that because the explain plan already uses hash aggregate (instead of the old sort) HashAggregate (cost=100278.16..104104.75 rows=382659 width=8) (actual time=7047.259..7050.261 rows=72 loops=1) which means this is at least 8.4. Plus the 'distinct' step uses less than 1% of total time, so even if you improve it the impact will be minimal. regards Tomas -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
