Guillaume Smet wrote:
Hello, We are experiencing performances problem with a quad Xeon MP and PostgreSQL 7.4 for a year now.
I had a similar issue with a client the other week.
Our context switch rate is not so high but the load of the server is blocked to 4 even on very high load and we have 60% cpu idle even in this case. Our database fits in RAM and we don't have any IO problem.
Actually, I think that's part of the problem - it's the memory bandwidth. > I saw this post from Tom Lane
http://archives.postgresql.org/pgsql-performance/2004-04/msg00249.php and several other references to problem with Xeon MP and I suspect our problems are related to this.
You should be seeing context-switching jump dramatically if it's the "classic" multi-Xeon problem. There's a point at which it seems to just escalate without a corresponding jump in activity.
We tried to put our production load on a dual standard Xeon on monday and it performs far better with the same configuration parameters. I know that work has been done by Tom for PostgreSQL 8.1 on multiprocessor support but I didn't find any information on if it solves the problem with Xeon MP or not.
I checked with Tom last week. Thread starts below: http://archives.postgresql.org/pgsql-hackers/2006-02/msg01118.php He's of the opinion that 8.1.3 will be an improvement.
My question is should we expect a resolution of our problem by switching to 8.1 or will we still have problems and should we consider a hardware change? We will try to upgrade next tuesday so we will have the real answer soon but if anyone has any experience or information on this, he will be very welcome.
-- Richard Huxton Archonet Ltd
