Re: [squid-users] How well does squid perform under stress?

On 4/4/07, Ben Spencer <ben.spencer@moody.edu> wrote:
> I did some research for an answer to this question, but, things tend to
> always resort to CPU usage and tuning (though, I did get some good
> information from those threads also).
>
> We have a squid appliance which is very heavy on CPU (which is
> expected). My question isn't really how can I tune it or why is it using
> so much CPU, but rather, how well does squid perform on a busy (CPU
> wise) box?

The exact behavior of a highly utilized cache is going to depend
greatly on the scheduler and IO subsystem of the host operating
system. In my experience (on Solaris and on BSD), Squid performance
tends to degrade quickly when cpu cycles are not available.

> I guess another way to ask is, does squid's performance scale linearly
> as the box (CPU specifically) usage increases or does performance
> actually degrade/level off once the CPU is approaches 100% utilization?
>
> Another question is: once the system is pushed to a maximum (or beyond),
> are things just slow or should abnormal behavior be expected?

Abnormal behavior should be expected. Specifically, time to service
each request does not scale linearly. Instead, as the CPU and IO
become saturated, "service time" increases logarithmically as the
number of concurrent outstanding sessions skyrockets.

It's trivial to deploy multiple parallel servers each running a single
Squid instance, so if your "squid appliance" is running out of CPU,
maybe it's time to add a couple of cache peers?

Kevin
Received on Wed Apr 04 2007 - 13:22:18 MDT