Hi, I have a query that is getting a pretty bad plan due to a massively incorrect count of expected rows. All tables in the query were vacuum analyzed right before the query was tested. Disabling nested loops gives a significantly faster result (4s vs 292s). Any thoughts on what I can change to make the planner generate a better plan? 32GB ram effective_cache_size = 16GB shared_buffers = 4GB random_page_cost = 1.5 default_statistics_target = 100 Note: for the tables in question, I tested default_statistics_target at 100, then also at 5000 to see if there was an improvement (none noted). select version(); version ------------------------------------------------------------------------------------------------------------------ PostgreSQL 8.4.2 on x86_64-redhat-linux-gnu, compiled by GCC gcc (GCC) 4.1.2 20071124 (Red Hat 4.1.2-42), 64-bit explain analyze select c.id, c.transactionid, c.clickgenerated, c.confirmed, c.rejected, cr.rejectedreason from conversion c inner join conversionrejected cr on cr.idconversion = c.id where date = '2010-11-06' and idaction = 12906 and idaffiliate = 198338 order by transactionid; QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------------------------------- Sort (cost=2318120.52..2345652.23 rows=11012683 width=78) (actual time=292668.896..292668.903 rows=70 loops=1) Sort Key: c.transactionid Sort Method: quicksort Memory: 43kB -> Nested Loop (cost=1234.69..715468.13 rows=11012683 width=78) (actual time=8687.314..292668.159 rows=70 loops=1) Join Filter: ((cr.idconversion = c.id) OR (c.id = 38441828354::bigint)) -> Append (cost=1234.69..1244.03 rows=2 width=56) (actual time=15.292..15.888 rows=72 loops=1) -> Bitmap Heap Scan on conversion c (cost=1234.69..1240.76 rows=1 width=31) (actual time=15.291..15.840 rows=72 loops=1) Recheck Cond: ((idaffiliate = 198338) AND (date = '2010-11-06'::date)) Filter: (idaction = 12906) -> BitmapAnd (cost=1234.69..1234.69 rows=4 width=0) (actual time=15.152..15.152 rows=0 loops=1) -> Bitmap Index Scan on conversion_idaffiliate_idx (cost=0.00..49.16 rows=3492 width=0) (actual time=4.071..4.071 rows=28844 loops=1) Index Cond: (idaffiliate = 198338) -> Bitmap Index Scan on conversion_date_idx (cost=0.00..1185.28 rows=79282 width=0) (actual time=10.343..10.343 rows=82400 loops=1) Index Cond: (date = '2010-11-06'::date) -> Index Scan using conversionlate_date_idx on conversionlate c (cost=0.00..3.27 rows=1 width=80) (actual time=0.005..0.005 rows=0 loops=1) Index Cond: (date = '2010-11-06'::date) Filter: ((idaction = 12906) AND (idaffiliate = 198338)) -> Seq Scan on conversionrejected cr (cost=0.00..191921.82 rows=11012682 width=31) (actual time=0.003..1515.816 rows=11012682 loops=72) Total runtime: 292668.992 ms select count(*) from conversionrejected ; count ---------- 11013488 Time: 3649.647 ms select count(*) from conversion where date = '2010-11-06'; count ------- 82400 Time: 507.985 ms select count(*) from conversion; count ---------- 73419376(1 row) Time: 7100.619 ms -- with enable_nestloop to off; -- much faster! QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Sort (cost=234463.54..234463.54 rows=2 width=78) (actual time=4035.340..4035.347 rows=70 loops=1) Sort Key: c.transactionid Sort Method: quicksort Memory: 43kB -> Hash Join (cost=1244.13..234463.53 rows=2 width=78) (actual time=4024.816..4034.715 rows=70 loops=1) Hash Cond: (cr.idconversion = c.id) -> Seq Scan on conversionrejected cr (cost=0.00..191921.82 rows=11012682 width=31) (actual time=0.003..1949.597 rows=11013576 loops=1) -> Hash (cost=1244.11..1244.11 rows=2 width=56) (actual time=19.312..19.312 rows=72 loops=1) -> Append (cost=1234.77..1244.11 rows=2 width=56) (actual time=18.539..19.261 rows=72 loops=1) -> Bitmap Heap Scan on conversion c (cost=1234.77..1240.83 rows=1 width=31) (actual time=18.538..19.235 rows=72 loops=1) Recheck Cond: ((idaffiliate = 198338) AND (date = '2010-11-06'::date)) Filter: (idaction = 12906) -> BitmapAnd (cost=1234.77..1234.77 rows=4 width=0) (actual time=18.237..18.237 rows=0 loops=1) -> Bitmap Index Scan on conversion_idaffiliate_idx (cost=0.00..49.16 rows=3492 width=0) (actual time=4.932..4.932 rows=28844 loops=1) Index Cond: (idaffiliate = 198338) -> Bitmap Index Scan on conversion_date_idx (cost=0.00..1185.36 rows=79292 width=0) (actual time=12.473..12.473 rows=82400 loops=1) Index Cond: (date = '2010-11-06'::date) -> Index Scan using conversionlate_date_idx on conversionlate c (cost=0.00..3.27 rows=1 width=80) (actual time=0.006..0.006 rows=0 loops=1) Index Cond: (date = '2010-11-06'::date) Filter: ((idaction = 12906) AND (idaffiliate = 198338)) Total runtime: 4035.439 ms -- for completeness, -- same query, on 9.0.0, underpowered server, 2 disks mirrored. Approximately the same table sizes/counts. select version(); version ------------------------------------------------------------------------------------------------------------------- PostgreSQL 9.0.0 on x86_64-unknown-linux-gnu, compiled by GCC gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-48), 64-bit QUERY PLAN ---------------------------------------------------------------------------------------------------------------------------------------------------------------------- Sort (cost=120727.25..120727.25 rows=2 width=78) (actual time=3214.827..3214.867 rows=70 loops=1) Sort Key: c.transactionid Sort Method: quicksort Memory: 43kB -> Nested Loop (cost=697.95..120727.24 rows=2 width=78) (actual time=2955.321..3214.208 rows=70 loops=1) -> Append (cost=697.95..120712.87 rows=2 width=56) (actual time=2931.584..3173.402 rows=72 loops=1) -> Bitmap Heap Scan on conversion c (cost=697.95..120706.59 rows=1 width=31) (actual time=2931.582..3150.231 rows=72 loops=1) Recheck Cond: (date = '2010-11-06'::date) Filter: ((idaction = 12906) AND (idaffiliate = 198338)) -> Bitmap Index Scan on conversion_date_idx (cost=0.00..697.95 rows=44365 width=0) (actual time=51.692..51.692 rows=82400 loops=1) Index Cond: (date = '2010-11-06'::date) -> Index Scan using conversionlate_idaffiliate_idx on conversionlate c (cost=0.00..6.27 rows=1 width=80) (actual time=23.091..23.091 rows=0 loops=1) Index Cond: (idaffiliate = 198338) Filter: ((date = '2010-11-06'::date) AND (idaction = 12906)) -> Index Scan using conversionrejected_pk on conversionrejected cr (cost=0.00..7.17 rows=1 width=31) (actual time=0.563..0.564 rows=1 loops=72) Index Cond: (cr.idconversion = c.id) Total runtime: 3214.972 ms Thanks, Bricklen -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance