Ivan Voras wrote:
PostgreSQL 9.0.1, 10 GB shared buffers, using pgbench with a scale
factor of 500 (7.5 GB database)
with pgbench -S (SELECT-queries only) the performance curve is:
-c# result
4 33549
8 64864
12 79491
16 79887
20 66957
24 52576
28 50406
32 49491
40 45535
50 39499
75 29415
Two suggestions to improve your results here:
1) Don't set shared_buffers to 10GB. There are some known issues with
large settings for that which may or may not be impacting your results.
Try 4GB instead, just to make sure you're not even on the edge of that area.
2) pgbench itself is known to become a bottleneck when running with lots
of clients. You should be using the "-j" option to spawn multiple
workers, probably 12 of them (one per core), to make some of this go
away. On the system I saw the most improvement here, I got a 15-25%
gain having more workers at the higher client counts.
The "sbwait" part is from FreeBSD - IPC sockets, but so much blocking
on semwait indicates large contention in PostgreSQL.
It will be interesting to see if that's different after the changes
suggested above.
--
Greg Smith 2ndQuadrant US greg@xxxxxxxxxxxxxxx Baltimore, MD
PostgreSQL Training, Services and Support www.2ndQuadrant.us
"PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books
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