On 9/14/10 9:10 AM, mark wrote:
Hello, I am relatively new to postgres (just a few months) so apologies if any of you are bearing with me. I am trying to get a rough idea of the amount of bang for the buck I might see if I put in a connection pooling service into the enviroment vs our current methodology of using persistent open connections. We have a number of in house applications that connect to a central Postgres instance. (8.3.7). The box is admitting underpowered with only 8 cores, and 8gb or ram and not great disk IO out of an MSA-70. the database is about 35GB on disk and does mainly (~95%) OTLP type queries. I am currently begging for more ram. Most of the connections from the various apps hold idle connections until they need to execute a query once done go back to holding an open idle connection. (there are ~600 open connections at any given time, and most of the time most are idle) this is typically fine while the number of active queries is low, but some other application (that doesn't use connection pooling or holding open connections when not in use) is hitting the db from time to time with 50-100 small queries (2ms queries from my testing) nearly all at once. when this happens the whole response time goes out the door however).
While connection pooling may be a good answer for you, there also appears to be a problem/bug in 8.3.x that may be biting you. My installation is very similar to yours (hundreds of idle "lightweight" connections, occasional heavy use by certain apps). Look at this thread: http://archives.postgresql.org/pgsql-performance/2010-04/msg00071.php On the server that's been upgraded to 8.4.4, we're not seeing this problem. But it's not in full production yet, so I can't say for sure that the CPU spikes are gone. (Unfortunately, the archives.postgresql.org HTML formatting is horrible -- why on Earth can't it wrap lines?) Craig
I think from reading this list for a few weeks the answer is move to using connection pooling package elsewhere to better manage incoming connections, with a lower number to the db. I am told this will require some re-working of some app code as I understand pg-pool was tried a while back in our QA environment and server parts of various in-house apps/scripts/..etc started to experience show stopping problems. to help make my case to the devs and various managers I was wondering if someone could expand on what extra work is having to be done while queries run and there is a high (500-600) number of open yet idle connections to db. lots of the queries executed use sub-transactions if that makes a difference. basically what I am paying extra for with that many persistent connections, that I might save if I go to the effort of getting the in-house stuff to make use of a connection pooler ? thank you for your time. ..: mark
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