Jesse Long wrote: > I have the following query, run immediately after executing VACUUM in > the database. There is only one connection to the database. You should run ANALYZE, not VACUUM. > The query runs for much longer than I expect it to run for, and I think > this is due to it using the incorrect subplan. As you can see, subplans > 1 and 3 make use of and index, but these subplans are not used. > Subplans and 4 are seqscan, and they are used. > > How can I get PostgreSQL to use subplan 1 and 3? They are only possible if an "Index Only Scan" is possible, which can only be used if the respective table entries are visible for all transactions. > testdb=> explain analyse SELECT * FROM ARCHIVE_DOCUMENT AS r0 WHERE r0.NODE_ID = 29 AND > r0.ARCHIVE_DATE >= '2013-07-08 18:28:00' AND (EXISTS (SELECT r1.* FROM ARCHIVE_DOCUMENT_INDEX AS r1 > WHERE r1.ARCHIVE_ID = r0.ID AND r1.NODE_ID = r0.NODE_ID AND r1.VALUE = 'BSH70002152' ) OR EXISTS ( > SELECT r2.* FROM ARCHIVE_DOCUMENT_INDEX AS r2 WHERE r2.ARCHIVE_ID = r0.ID AND r2.NODE_ID = r0.NODE_ID > AND r2.VALUE = 'TC212592' ) ) ORDER BY r0.ARCHIVE_DATE DESC LIMIT 10; [...] > Filter: ((alternatives: SubPlan 1 or hashed SubPlan 2) OR (alternatives: SubPlan 3 or hashed > SubPlan 4)) > > Rows Removed by Filter: 710851 > > SubPlan 1 > > -> Index Only Scan using archive_document_index_x_archive_id_node_id_value on > archive_document_index r1 (cost=0.57..4.59 rows=1 width=0) (never executed) > > Index Cond: ((archive_id = r0.id) AND (node_id = r0.node_id) AND (value = > 'BSH70002152'::text)) > > Heap Fetches: 0 > > SubPlan 2 > > -> Seq Scan on archive_document_index r1_1 (cost=0.00..1958104.00 rows=1520 width=16) > (actual time=44418.383..44558.293 rows=4 loops=1) > > Filter: ((value)::text = 'BSH70002152'::text) > > Rows Removed by Filter: 95009919 > > SubPlan 3 > > -> Index Only Scan using archive_document_index_x_archive_id_node_id_value on > archive_document_index r2 (cost=0.57..4.59 rows=1 width=0) (never executed) > > Index Cond: ((archive_id = r0.id) AND (node_id = r0.node_id) AND (value = > 'TC212592'::text)) > > Heap Fetches: 0 > > SubPlan 4 > > -> Seq Scan on archive_document_index r2_1 (cost=0.00..1958104.00 rows=1520 width=16) > (actual time=41659.464..41663.342 rows=1 loops=1) > > Filter: ((value)::text = 'TC212592'::text) > > Rows Removed by Filter: 95009922 The estimates are quite off. Does "ANALYZE archive_document", possibly after increasing default_statistics_target, make a difference? Yours, Laurenz Albe -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
