Re: [squid-users] cache_swap_low and cache_swap_high

On Wed, 5 Nov 2003, Raja R wrote:

> Can you pls explain the cache_swap_low and cache_swap_high params w.r.t the
> performance and if I can tune up any other params to speed up my proxy
> server ?

Not really related to performance. Just parameters used when maintainign
the already cached content and discarding old content.

I would recommend starting by doing some statistical analysis of your
server to try to determine what is causing the bottleneck:

* Amount of traffic to/from your clients
* Amount of traffic to/from the Internet link
* CPU utilisation
* Memory & Swap usage levels
* Disk I/O usage levels ("iostat -i 5" gives a good view of this)


What I can give as guidance is that when a Squid proxy feels slow the
reasons usually is one of the following:

* The Internet link is overloaded
- other traffic chewing up the link such as various peer-to-peer file
sharing networks, viruses etc.
- too small Internet link in relation to the demands from your users
* The Squid server is out of memory, pushing Squid into swap.
- cache_mem too high
- too little memory in relation to your cache_dir size
- other applications on the same server using a lot of memory
* The disk I/O subsytem is overloaded, causing Squid to wait a lot for
the harddrive.
- ufs cache_dir type and high request rate (30req/s or more)
- aufs/diskd cache_dir type and simply too few harddrives to keep up
with the rate required


as you can see the reasons and solutions can vary a lot, and without
knowing in more detail where the bottleneck may be it is hard to give a
good advice on what to change. But all the cases above is easily
identified by normal system & Internet link monitoring tools.

Regards
Henrik