I just noticed that PG10 CREATE STATISTICS (dependencies) doesn't seem to work for joins on multiple columns; is that right? With statistics on table for 20171111 but not 20171110: ts=# CREATE STATISTICS x ON site_id,sect_id FROM eric_enodeb_cell_20171111; ts=# ANALYZE VERBOSE eric_enodeb_cell_20171111; ts=# explain ANALYZE SELECT FROM eric_enodeb_cell_20171110 a JOIN eric_enodeb_cell_20171110 b USING(start_time, sect_id) WHERE a.site_id=318 AND sect_id=1489; Nested Loop (cost=0.83..4565.09 rows=1 width=0) (actual time=23.595..69.541 rows=96 loops=1) => bad estimate on redundant WHERE WITHOUT multivar statistics ts=# explain ANALYZE SELECT FROM eric_enodeb_cell_20171111 a JOIN eric_enodeb_cell_20171111 b USING(start_time, sect_id) WHERE a.site_id=318 AND sect_id=1489; Nested Loop (cost=0.83..4862.41 rows=96 width=0) (actual time=0.034..3.882 rows=96 loops=1) => good estimate on redundant WHERE WITH multivar statistics ts=# explain ANALYZE SELECT FROM eric_enodeb_cell_20171110 a JOIN eric_enodeb_cell_20171110 b USING(start_time, sect_id); Merge Join (cost=18249.85..19624.18 rows=54858 width=0) (actual time=157.252..236.945 rows=55050 loops=1) => good estimate on JOIN on SECT_id without stats ts=# explain ANALYZE SELECT FROM eric_enodeb_cell_20171110 a JOIN eric_enodeb_cell_20171110 b USING(start_time, site_id); Merge Join (cost=0.83..14431.81 rows=261499 width=0) (actual time=0.031..259.382 rows=262638 loops=1) => good estimate on JOIN on SITE_id without stats ts=# explain ANALYZE SELECT FROM eric_enodeb_cell_20171111 a JOIN eric_enodeb_cell_20171111 b USING(start_time, site_id); Merge Join (cost=0.83..14706.29 rows=268057 width=0) (actual time=37.360..331.276 rows=268092 loops=1) => good estimate on JOIN on SITE_id with stats ts=# explain ANALYZE SELECT FROM eric_enodeb_cell_20171111 a JOIN eric_enodeb_cell_20171111 b USING(start_time, sect_id); Merge Join (cost=18560.89..19959.67 rows=55944 width=0) (actual time=130.865..198.439 rows=55956 loops=1) => good estimate on JOIN on SECT_id with stats ts=# explain ANALYZE SELECT FROM eric_enodeb_cell_20171111 a JOIN eric_enodeb_cell_20171111 b USING(start_time, sect_id, site_id); Gather (cost=1000.83..12222.06 rows=460 width=0) (actual time=1.686..149.707 rows=55956 loops=1) => poor estimate on redundant JOIN WITH stats (??) I've already fixed our reports to avoid this kind of thing and support our PG95 customers, but I tentatively would've expected PG10 MV stats to "know" that USING(site_id, sect_id) is no more selective than USING(sect_id), same as it knows that's true for WHERE site... AND sect.... Justin -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
