Обсуждение: Performance issue
Hello, I have been trying to get my Postgres database to do faster inserts. The environment is basically a single user situation. The part that I would like to speed up is when a User copys a Project. A Project consists of a number of Rooms(say 60). Each room contains a number of items. A project will contain say 20,000 records. Anyway the copying process gets slower and slower, as more projects are added to the database. My statistics(Athlon 1.8Ghz) ---------------- 20,000 items Takes on average 0.078seconds/room 385,000 items Takes on average .11seconds/room 690,000 items takes on average .270seconds/room 1,028,000 items Takes on average .475seconds/room As can be seen the time taken to process each room increases. A commit occurs when a room has been copied. The hard drive is not being driven very hard. The hard drive light only flashes about twice a second when there are a million records in the database. I thought that the problem could have been my plpgsql procedure because I assume the code is interpreted. However I have just rewriten the code using straight sql(with some temp fields), and the times turn out to be almost exactly the same as the plpgsql version. The read speed for the Application is fine. The sql planner seems to be doing a good job. There has been only one problem that I have found with one huge select, which was fixed by a cross join. I am running Red hat 8. Some of my conf entries that I have changed follow shared_buffers = 3700 effective_cache_size = 4000 sort_mem = 32168 Are the increasing times reasonable? The times themselves might look slow, but thats because there are a number of tables involved in a Copy I can increase the shared buffer sizes above 32M, but would this really help? TIA peter Mcgregor
Peter, One possibility is to drop all the indexes, do the insert and re-add the indexes. The more indexes that exist and the more rows that exist, the more costly the insert. Regards, Joseph At 05:48 PM 9/24/2003 +1200, peter wrote: >Hello, > >I have been trying to get my Postgres database to do faster inserts. > >The environment is basically a single user situation. > >The part that I would like to speed up is when a User copys a Project. >A Project consists of a number of Rooms(say 60). Each room contains a >number of items. >A project will contain say 20,000 records. > >Anyway the copying process gets slower and slower, as more projects are >added to the database. > >My statistics(Athlon 1.8Ghz) >---------------- >20,000 items Takes on average 0.078seconds/room >385,000 items Takes on average .11seconds/room >690,000 items takes on average .270seconds/room >1,028,000 items Takes on average .475seconds/room > >As can be seen the time taken to process each room increases. A commit >occurs when a room has been copied. >The hard drive is not being driven very hard. The hard drive light only >flashes about twice a second when there are a million records in the database. > >I thought that the problem could have been my plpgsql procedure because I >assume the code is interpreted. >However I have just rewriten the code using straight sql(with some temp >fields), >and the times turn out to be almost exactly the same as the plpgsql version. > >The read speed for the Application is fine. The sql planner seems to be >doing a good job. There has been only one problem >that I have found with one huge select, which was fixed by a cross join. > > I am running Red hat 8. Some of my conf entries that I have changed follow >shared_buffers = 3700 >effective_cache_size = 4000 >sort_mem = 32168 > >Are the increasing times reasonable? >The times themselves might look slow, but thats because there are a number >of tables involved in a Copy > >I can increase the shared buffer sizes above 32M, but would this really help? > >TIA > >peter Mcgregor > > >---------------------------(end of broadcast)--------------------------- >TIP 4: Don't 'kill -9' the postmaster
get rid of any unnecessary indexes? i've found that droping indexes and re-creating them isn't usually worth the effort mount the disk with the noatime option which saves you the time involved in updating the last access time on files make sure you're doing all the inserts in one transaction.. wrapping a bunch of INSERTS in BEGIN & COMMIT speeds them up loads. > At 05:48 PM 9/24/2003 +1200, peter wrote: > >Hello, > > > >I have been trying to get my Postgres database to do faster inserts. > > > >The environment is basically a single user situation. > > > >The part that I would like to speed up is when a User copys a Project. > >A Project consists of a number of Rooms(say 60). Each room contains a > >number of items. > >A project will contain say 20,000 records. > > > >Anyway the copying process gets slower and slower, as more projects are > >added to the database. > > > >My statistics(Athlon 1.8Ghz) > >---------------- > >20,000 items Takes on average 0.078seconds/room > >385,000 items Takes on average .11seconds/room > >690,000 items takes on average .270seconds/room > >1,028,000 items Takes on average .475seconds/room > > > >As can be seen the time taken to process each room increases. A commit > >occurs when a room has been copied. > >The hard drive is not being driven very hard. The hard drive light only > >flashes about twice a second when there are a million records in the > > database. > > > >I thought that the problem could have been my plpgsql procedure because I > >assume the code is interpreted. > >However I have just rewriten the code using straight sql(with some temp > >fields), > >and the times turn out to be almost exactly the same as the plpgsql > > version. > > > >The read speed for the Application is fine. The sql planner seems to be > >doing a good job. There has been only one problem > >that I have found with one huge select, which was fixed by a cross join. > > > > I am running Red hat 8. Some of my conf entries that I have changed > > follow shared_buffers = 3700 > >effective_cache_size = 4000 > >sort_mem = 32168 > > > >Are the increasing times reasonable? > >The times themselves might look slow, but thats because there are a number > >of tables involved in a Copy > > > >I can increase the shared buffer sizes above 32M, but would this really > > help? > > > >TIA > > > >peter Mcgregor > > > > > >---------------------------(end of broadcast)--------------------------- > >TIP 4: Don't 'kill -9' the postmaster > > ---------------------------(end of broadcast)--------------------------- > TIP 2: you can get off all lists at once with the unregister command > (send "unregister YourEmailAddressHere" to majordomo@postgresql.org)
> My statistics(Athlon 1.8Ghz) > ---------------- > 20,000 items Takes on average 0.078seconds/room > 385,000 items Takes on average .11seconds/room > 690,000 items takes on average .270seconds/room > 1,028,000 items Takes on average .475seconds/room [snip] > I am running Red hat 8. Some of my conf entries that I have changed > follow > shared_buffers = 3700 > effective_cache_size = 4000 > sort_mem = 32168 Have you twiddled with your wal_buffers or checkpoint_segments? Might be something to look at. -sc -- Sean Chittenden
> 20,000 items Takes on average 0.078seconds/room > 385,000 items Takes on average .11seconds/room > 690,000 items takes on average .270seconds/room > 1,028,000 items Takes on average .475seconds/room > > As can be seen the time taken to process each room increases. A commit > occurs when a room has been copied. It probably isn't the insert that is getting slower, but a select. Foreign keys to growing tables will exhibit this behaviour. Since the time is doubling with the number of items, you might want to check for a SELECT working with a sequential scan rather than an index scan.