> -----Original Message----- > From: pgsql-performance-owner@xxxxxxxxxxxxxx [mailto:pgsql-performance- > owner@xxxxxxxxxxxxxx] On Behalf Of Ivan Voras > Sent: Wednesday, January 26, 2011 6:25 AM > To: pgsql-performance@xxxxxxxxxxxxxx > Subject: Re: Queries becoming slow under heavy load > > On 25/01/2011 22:37, Anne Rosset wrote: > > Hi, > > > > We are running some performances tests. With a lot of concurrent > > access, queries get very slow. When there is no load, those queries > run > > fast. > > As others said, you need to stat how many concurrent clients are > working > on the database and also the number of logical CPUs (CPU cores, > hyperthreading) are present in the machine. So far, as a rule of thumb, > if you have more concurrent active connections (i.e. doing queries, not > idling), you will experience a sharp decline in performance if this > number exceeds the number of logical CPUs in the machine. > Depending on what version the OP is running - I didn't see where a version was givin - if there is a "lot" number of idle connections it can affect things as well. Tom indicated to me this should be "much better" in 8.4 and later. <slight deviation to put idle connections overhead in prespecive> We cut our idle connections from 600+ to a bit over 300 and saw a good drop in box load and query responsiveness. (still get large user cpu load spikes though when a few hundred idle connection processes are woken open because they all appear to be sleeping on the same semaphore and one of them has work to do. ) (yeah I know get a pooler, to bad only bouncer seems to pool out idle connections with transaction pooling but then I lose prepared statements... I am still working on that part and getting off 8.3. yes our app tried to do its own quasi connection pooling. When we deployed the app on a few hundred boxes the error of this choice years ago when this app lived on much fewer machines is now pretty evident.) > > -- > Sent via pgsql-performance mailing list (pgsql- > performance@xxxxxxxxxxxxxx) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
