[PERFORM] query uses index but takes too much time?
hello to all, i would like your advice on the following matter. i have a table with 150 million rows. there are some indexes on this table but the one that is really important is one that has 3 columns (a,b,c). one application constantly makes queries and the query planner uses this index to narrow down the final set of results. so usually from 150 millions, when the 3 conditions have been applied, the remaining rows to be checked are about 20-300. So these queries are very fast, and take from 10-100 ms usually. There is a special case where these 3 conditions narrow down the final set to 15.000 rows so the server must check all these rows. The result is that the query takes around 1 minute to complete. Is that a normal time for the execution of the query? i know that most of you will send me the link with the guide to reporting slow queries but that's not the point at the moment. i am not looking for a specific answer why this is happening. i just want to know if that seems strange to more people than just me and if i should look into that. but if for the above you need to have a clearer picture of the server then: -red hat 5.6 -32 cores, -96GB ram -fiber storage (4GBps) -postgresql 9.0.5 -shared_buffers : 25 GB -not i/o bound (too many disks, different partitions for backup, archives, xlogs, indexes) -not cpu bound (the cpu util was about 5% when i performed the tests) -the query planner values on postgresql.conf are the default -i also performed the tests on the hot-standby with the same results -the query plan is the correct one, indicating that it should use the correct index -i forced index_scan to off and then it used bitmap heap scan with similar results. -i forced bitmap heap scan to off and then it did a seq scan any ideas? thx in advance for your insight -- View this message in context: http://postgresql.1045698.n5.nabble.com/query-uses-index-but-takes-too-much-time-tp5020742p5020742.html Sent from the PostgreSQL - performance mailing list archive at Nabble.com. -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] query uses index but takes too much time?
On Thu, Nov 24, 2011 at 12:20 PM, MirrorX mirr...@gmail.com wrote: -32 cores, -not cpu bound (the cpu util was about 5% when i performed the tests) A single query will only use a single CPU. 5% of 32 cores is 100% of 1.6 cores. Are you sure that the 1 core doing the 1 postgresql query wasn't 100% utilized? a. -- Aidan Van Dyk Create like a god, ai...@highrise.ca command like a king, http://www.highrise.ca/ work like a slave. -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] query uses index but takes too much time?
Le 24 novembre 2011 18:20, MirrorX mirr...@gmail.com a écrit : hello to all, i would like your advice on the following matter. i have a table with 150 million rows. there are some indexes on this table but the one that is really important is one that has 3 columns (a,b,c). one application constantly makes queries and the query planner uses this index to narrow down the final set of results. so usually from 150 millions, when the 3 conditions have been applied, the remaining rows to be checked are about 20-300. So these queries are very fast, and take from 10-100 ms usually. There is a special case where these 3 conditions narrow down the final set to 15.000 rows so the server must check all these rows. The result is that the query takes around 1 minute to complete. Is that a normal time for the execution of the query? i know that most of you will send me the link with the guide to reporting slow queries but that's not the point at the moment. i am not looking for a specific answer why this is happening. i just want to know if that seems strange to more people than just me and if i should look into that. but if for the above you need to have a clearer picture of the server then: -red hat 5.6 -32 cores, -96GB ram -fiber storage (4GBps) -postgresql 9.0.5 -shared_buffers : 25 GB -not i/o bound (too many disks, different partitions for backup, archives, xlogs, indexes) -not cpu bound (the cpu util was about 5% when i performed the tests) -the query planner values on postgresql.conf are the default -i also performed the tests on the hot-standby with the same results -the query plan is the correct one, indicating that it should use the correct index -i forced index_scan to off and then it used bitmap heap scan with similar results. -i forced bitmap heap scan to off and then it did a seq scan any ideas? thx in advance for your insight not it is not that strange. It can be several things that lead you to this situation. -- View this message in context: http://postgresql.1045698.n5.nabble.com/query-uses-index-but-takes-too-much-time-tp5020742p5020742.html Sent from the PostgreSQL - performance mailing list archive at Nabble.com. -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance -- Cédric Villemain +33 (0)6 20 30 22 52 http://2ndQuadrant.fr/ PostgreSQL: Support 24x7 - Développement, Expertise et Formation -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
