Le 24 novembre 2011 18:20, MirrorX <mirrorx@xxxxxxxxx> 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@xxxxxxxxxxxxxx) > 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@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
