Re: processor running queue - general rule of thumb?

Alan McKay wrote:
> Hey folks,
> We did 4 tests, upping the load each time.   The 3rd and 4th ones have
> all 8 cores pegged at about 95%.  Yikes!
>
> In the first test the processor running queue spikes at 7 and maybe
> averages 4 or 5
>
> In the last test it spikes at 33 with an average maybe 25.
>
> Looks to me like it could be a CPU bottleneck.  But I'm new at this :-)
>
> Is there a general rule of thumb "if queue is longer than X, it is
> likely a bottleneck?"
>
> In reading an IBM Redbook on Linux performance, I also see this :
> "High numbers of context switches in connection with a large number of
> interrupts can signal driver or application issues."
>
> On my first test where the CPU is not pegged, context switching goes
> from about 3700 to about 4900, maybe averaging 4100
>
>
>

Well the people here will need allot more information to figure out what
is going on.

What kind of Stress did you do???? is it a specific  query causing the
problem in the test
What kind of load?
How many simulated clients
How big is the database?

Need to see the postgresql.config

What kind of IO Subsystem do you have ???
what does vmstat show

have you look at wiki yet
http://wiki.postgresql.org/wiki/Performance_Optimization