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Re: High load on Squid server after change from reiserfs to ext3



----- Original Message -----
From: "Andreas Dilger" <adilger clusterfs com>
To: "Andreas Jung" <andreas zope com>
Cc: <ext3-users redhat com>
Sent: Friday, May 24, 2002 14:11
Subject: Re: High load on Squid server after change from reiserfs to ext3


> On May 24, 2002  13:40 -0400, Andreas Jung wrote:
> > From: "Andreas Dilger" <adilger clusterfs com>
> > > One simple question - does the increase in the load value actually
> > > affect squid performance?  You say there is no increase in CPU
> > > utilization.  That may be good or it may be bad, depending if the
"idle"
> > > CPU is actually waiting on I/O to complete.
> > >
> > > What does the output of vmstat on both systems show?  Please send two
> > > traces, one during low load and one during high load.
> >
> > Our big brother diagrams show that the CPU utilization remains *low* all
> > the time. I have been running vmstat on both machines when one of the
> > machine had a spike. But both machines showed more ore less identical
> > vmstat output:  CPU was about 85% idle, no swapping, not much interrupts
> > and context switches.
> > In general, vmstat showed a perfect behaviour except that the load
average
> > went up on one box.
>
> Then it is nothing to worry about.  The "load average" does not indicate
> anything other than the number of processes runnable or waiting for
> disk I/O.  It is likely that when you are doing a large journal flush
> the kjournald process is waiting for the disk I/O to complete, so it is
> counted 1 towards the load average.  This in itself does not affect the
> performance of the system.
>


That's right but we see these spikes sometimes over a period of 3-4 hours.
And there is only a moderate disk IO during that time of about 2GB/hour
since
the squids have a very high overall highrate of 96% (50% memory hits).

Andreas





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