varnish crashes

[Michael S. Fischer]

On Jan 24, 2010, at 10:40 AM, Angelo Höngens wrote:
> 
> According to top, the CPU usage for the varnishd process is 0.0% at 400
> req/sec. The load over the past 15 minutes is 0.45, probably mostly
> because of haproxy running on the same machine. So I don't think load is
> a problem.. My problem is that varnish sometimes just crashes or stops
> responding.
> 
> My hit cache ratio is not that high, around 80%, and the backend servers
> can be slow at times (quite complex .net web apps). But I've changed
> some settings, and I am waiting for the next time varnish starts to stop
> responding.. I'm beginning to think it's something that grows over time,
> after restarting the varnish process things tend to run smooth for a
> while. I'll just keep monitoring it.

The other most common reason why the varnish supervisor can start killing off children is when they are blocked waiting on a page-in, which is usually due to VM overcommit (i.e., storage file size significantly exceeds RAM and you have a very large hot working set).   You can usually see that when "iostat -x" output shows the I/O busy % is close to 100, meaning the disk is saturated.   You can also see that in vmstat (look at the pi/po columns if you're using a file, or si/so if you're using malloc).

--Michael

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