Andrew Jorgensen andrew at jorgensenfamily.us
Tue Sep 30 17:03:03 MDT 2008

On Tue, Sep 30, 2008 at 4:54 PM, Michael Torrie <torriem at gmail.com> wrote:
> When the load is high, the first thing to check is the amount of swap
> being used.  If the swap is exceeding 50%, I've found that Linux tends
> to thrash a lot.  In this case adding RAM will help, although if this is
> not a normal server condition, maybe you have a process with a memory leak.

We suspected this, of course, but it appears that swap is not in use.
SwapTotal == SwapFree means what I think it does, doesn't it?

> If not, then check your disk i/o stats.  If the disk is maxed out, or
> even in action the majority of the time, then your load average is due
> to disk wait, which is a hard one to solve.  Sometimes a better i/o
> scheduler can improve things.  Sometimes faster disks.

How do we check these stats?

> If it's none of these things, then perhaps it's the network that
> processes are waiting on.  This isn't necessarily a bandwidth issue
> either.  If NFS is slow, the load average will shoot up, for example.

What tools can I use to see if network is bottlenecking here?  I doubt
that's it but if it's not disk IO then I do need to check there.

> So load is caused by I/O problems, whether disk or network.

Can it also be caused, for instance, by an apache thread waiting for
mysql to respond?  If so then how do I tell if that's the case?

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