Hello, I am having a performance issue after upgrade from 8.4.20-1 -> 9.3.5. I am running on CentOS 2.6.32-431.29.2.el6.x86_64 #1 SMP Tue Sep 9 21:36:05 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux. Upgrade was without any issues, I used pg_upgrade. One of my queries now takes cca 100x more time than it used to. The query is: http://pastebin.com/uUe16SkR explain from postgre 8.4.20-1: http://pastebin.com/r3WRHzSM explain from postgre 9.3.5: http://pastebin.com/hmNxFiDL The problematic part seems to be this (postgresql 93 version): SubPlan 17 -> Limit (cost=8.29..8.41 rows=1 width=11) InitPlan 16 (returns $19) -> Index Scan using t_store_info_pkey on t_store_info s_7 (cost=0.28..8.29 rows=1 width=8) Index Cond: (id = 87::bigint) -> Nested Loop (cost=0.00..72351.91 rows=624663 width=11) -> Seq Scan on t_pn pn (cost=0.00..37498.65 rows=1 width=11) <<-----!!!! Filter: ((max(w.item_ean) = ean) AND (company_fk = $19)) -> Seq Scan on t_weighting w4 (cost=0.00..28606.63 rows=624663 width=0) this row: Seq Scan on t_pn pn (cost=0.00..37498.65 rows=1 width=11) in 8.4 explain looks like this: -> Index Scan using inx_pn_companyfk_ean on t_pn pn (cost=0.00..8.64 rows=1 width=11) Index Cond: ((company_fk = $19) AND ($20 = ean)) As You can see, 8.4 is using index scan on the table, 9.3 is using seq scan. The relevant index does exist in both databases. So I tried to force 9.3 to use the index by: set enable_seqscan = off; Now explain analyze looks like this: http://pastebin.com/kR7qr39u the relevant problematic part is: SubPlan 17w.stat_count_entered IS NULL AND w.stat_weight_start IS NULL)) -> Limit (cost=9.15..9.31 rows=1 width=11) InitPlan 16 (returns $19) -> Index Scan using t_store_info_pkey on t_store_info s_7 (cost=0.28..8.29 rows=1 width=8) Index Cond: (id = 87::bigint) -> Nested Loop (cost=0.85..102881.78 rows=624667 width=11) -> Index Only Scan using int_t_weighting_coordinates on t_weighting w4 (cost=0.42..95064.99 rows=624667 <<---- !!! -> Materialize (cost=0.43..8.45 rows=1 width=11) -> Index Scan using inx_pn_companyfk_ean on t_pn pn (cost=0.43..8.45 rows=1 width=11) Index Cond: ((company_fk = $19) AND (max(w.item_ean) = ean)) So planner is now using index scan. Query execution time with this is around 4.2 s (roughly same as in postgre 8.4) , with enable_seqscan=on it is around 360s (2 orders of magnitude higher than with postgre 8.4). What is interesting is, that query cost is roughly the same in both situations. My questions are: 1. how to set postgresql / modify query / create some indexes / whatever, to get the same query running time in postgresql 9.3 as I had in 8.4 2. how is it possible for analyze to get same costs when the query running time is almost 100x higher. Thank You for any ideas on this. -- Matúš Svrček svrcek@xxxxxxxxxxxx -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
