Hi Tom,
I now have excluded ntp as root cause for the CPU cycles being wasted in user space.
I installed perf and monitored two servers (with different postgresql versions and hardware specification) which are "hanging" and have some output. Since I'm no die-hard at interpreting the output of perf top what would be the next step to do?
Would it be a good idea to a) read the perf manual and/or 2) provide the output of perf top as a first step to see what is going on?
What I think I see is a lot spin_lock_irq and scheduler processes active.
Any guidance much appreciated.
Most Regards,
Dennis Brouwer
M4N
On Mon, Sep 24, 2012 at 6:30 PM, Tom Lane
<tgl@sss.pgh.pa.us> wrote:
Dennis Brouwer <
dennis.brouwer@m4n.nl> writes:
> Last week I was repeatedly able to run all these tests on the database
> without any issue but recently, all of a sudden at random, some of the
> queries performed a factor 100 less. It may take hours to complete the
> transaction. At the same moment we see a dramatic decrease in IO and the
> CPU is nearly 100% busy in user space.
> After days of testing I may have found the cause: the ntp client. If I stop
> the ntp client the problem vanishes.
> I have started reading on spinlocks and other related material but this all
> is rather complicated stuff and kindly ask in what direction I should
> search. The issue can be reproduced for both postgresql-9.1 and
> postgresql-9.2 and perhaps can be rephrased as: Very high CPU load in user
> space (at random) with ntp enabled and (long?) running transactions.
configured to adjust the system clock by slewing, or by stepping? Can
you identify what part of the code is eating CPU (try perf or oprofile)?
regards, tom lane