Select max(primary_key) taking a long time
От | Francisco Reyes |
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Тема | Select max(primary_key) taking a long time |
Дата | |
Msg-id | cone.1274454081.672731.11718.1000@shelca обсуждение исходный текст |
Ответы |
Re: Select max(primary_key) taking a long time
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Список | pgsql-general |
Postgres 8.4.1 CentOS 5.4 I am trying to do select max(primary_key) from some_table; The explain looks like: explain select max(primary_key) from some_table; QUERY PLAN ---------------------------------------------------------------------------- Result (cost=0.15..0.16 rows=1 width=0) InitPlan 1 (returns $0) -> Limit (cost=0.00..0.15 rows=1 width=8) -> Index Scan Backward using some_table_pkey on some_table (cost=0.00..161797059.16 rows=1086279613 width=8) Filter: (trans_id IS NOT NULL) I checked there wasn't a lock of any kind select waiting from pg_stat_activity; waiting --------- f f f f f f f (7 rows) IOwait on the machine is around 20% sar 10 5 Linux 2.6.18-128.el5 (trans05.afs) 05/21/2010 10:56:49 AM CPU %user %nice %system %iowait %steal %idle 10:56:59 AM all 5.90 0.00 2.04 20.67 0.00 71.39 10:57:09 AM all 5.90 0.00 1.99 23.36 0.00 68.75 10:57:19 AM all 5.87 0.00 2.10 22.56 0.00 69.47 10:57:29 AM all 5.84 0.00 2.09 23.56 0.00 68.51 10:57:39 AM all 6.30 0.00 2.23 21.53 0.00 69.94 Average: all 5.96 0.00 2.09 22.34 0.00 69.61 Any ideas why the select would be taking long.. It has gone on for minutes with no answer. I can just look at the value of the sequence for the primary key, but I am curious why something that usually is sub-second is taking so long..
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