On 3/12/2007 8:50 PM, Alexey Popov wrote:
Hi

Alexey Popov wrote:
Now we also have terribly performing PostgreSQL on 8-core server. We noticed the slowdown after moving PostgreSQL from 2xXeon 3.0 Apache+PostgreSQL server to dedicated PostgreSQL server. I collected some stats (see attach) before moving to Linux.
Sorry for the broken top ouptut in previuos message. Here's the correct one.

last pid: 70857;  load averages: 35.05, 37.11, 33 up 25+23:08:00  12:46:29
94 processes:  46 running, 48 sleeping
CPU: 17.0% user,  0.0% nice, 80.5% system,  0.2% interrupt,  2.3% idle
Mem: 1209M Active, 1890M Inact, 494M Wired, 143M Cache, 214M Buf, 127M Free
Swap: 2048M Total, 72K Used, 2048M Free

Have you tried testing with different values for kern.hz? I am by no means an expert, but have stumbled across various postings over the past few years that suggest the high value (1000) used by modern (5.x+?) kernels can be pessimistic for some workloads...

If you could try testing with some other values by setting in /boot/loader.conf, eg:

    kern.hz="100"

Perhaps testing 100 and 200 to see how they fare against the default value of 1000, would at least provide some indicator as to whether this has any bearing on performance.

Some with a better knowledge of the kernel internals may be able to support or dimiss this idea, but as Kris is off on holidays I figured any suggestion was worthwhile! ;-)

I'd also like to say thanks for your efforts to help test and track down the cause of these performance problems - in the end the whole community benefits, so the more you are able to test and help resolve these things the better for us all... :-)

--Antony
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