On Fri, Feb 4, 2011 at 7:08 AM, Ivan Voras <ivoras@xxxxxxxxxxx> wrote: > -> BitmapAnd (cost=1282.94..1282.94 > rows=1430 width=0) (actual time=5.508..5.508 rows=0 loops=1) > -> Bitmap Index Scan on > news_index_layout_id_state (cost=0.00..150.14 rows=2587 width=0) (actual > time=0.909..0.909 rows=3464 loops=1) > Index Cond: ((layout_id = 8980) > AND (state = 2)) > -> BitmapOr (cost=1132.20..1132.20 > rows=20127 width=0) (actual time=4.136..4.136 rows=0 loops=1) > -> Bitmap Index Scan on > news_visible_from (cost=0.00..1122.09 rows=19976 width=0) (actual > time=3.367..3.367 rows=19932 loops=1) > Index Cond: (visible_from > IS NULL) > -> Bitmap Index Scan on > news_visible_to (cost=0.00..9.40 rows=151 width=0) (actual > time=0.766..0.766 rows=43 loops=1) > Index Cond: (1296806570 <= > visible_to) I think this part of the query is the problem. Since the planner doesn't support cross-column statistics, it can't spot the correlation between these different search conditions, resulting in a badly broken selectivity estimate. Sometimes you can work around this by adding a single column, computed with a trigger, that contains enough information to test the whole WHERE-clause condition using a single indexable test against the column value. Or sometimes you can get around it by partitioning the data into multiple tables, say with the visible_from IS NULL rows in a different table from the rest. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
