Re: [squid-users] Tuning the cache with heavy load

On 18/07/11 21:05, Francesco wrote:
> Hello,
>
> i have got a Squid version 3.1.8 running on a CentOS 5.x.
> Since it works for url and content filtering, in conjunction with
> Dansguardian in front, for some hunderd of users, the load average of that
> machine is sometimes very high (also 5.0 or 8.0...).

Check your config for regex ACLs. They slow squid down. A lot. Simple
tuning such as dstdomain instead of domain regex can raise the req/sec
rates up easily.

> The biggest process is squid, both on CPUs and Memory; i noticed, by

Squid-3 is not very efficient with CPU yet. We are still optimizing that
down after the new feature additions. It also uses RAM cache a lot more.

> entering top -s and press "1" - that often the system is in wait, perhaps
> it waits for the disk IO subsystem to write and manage Squid's cache.

Very likely. Check your disk I/O stats as well.

>
> I tried to make some customization in cache tuning, thinking that the
> bottleneck are disks, so i reduce the cache size.

Okay, confirmation that disk is one of the bottlenecks for you.

>
> Something is getting better, but the system is still very loaded.
>
> Are there some general suggestions to privilege speed and not bandwidth,
> for systems with very high load?

* AUFS cache format on CentOS. This one is specific.

* JBOD configuration spread over more disks. Avoid RAID unless you have
high quality H/W controllers. Squid thrashes the disks with mostly
random-access writes and byte-hit-ratio proportion of random-access reads.

* Faster disks, you can get a good +50% speed out of 15Krpm over 10Krpm
according to the I/O benchmarks from last year.

* Possibly an SSD drive for small objects cache_dir (use min-size and
max-size to tune).

If this is still a big problem after tuning you may want to get in touch
with The Measurement Factory about a build of squid 3.2 with rock
storage. That is the new replacement for COSS and does SMP support as
well as disk backed slices.

Amos

-- 
Please be using
   Current Stable Squid 2.7.STABLE9 or 3.1.14
   Beta testers wanted for 3.2.0.9