September 22, 2010

Optimizing SQUID - (Part 2)

Subject: Squid's cache_swap_low & cache_swap_high disk space watermarks

In continuation to my testing of squid for optimization [refer Optimizing SQUID - (Part 1) ] , I then used Squid's configuration directive cache_swap_low and cache_swap_high. Thus performance of squid does improves but probably it won't be  noticeable. But, it definately reduces the chances  of squid's slow down or performance degradation.

The cache_swap_low and cache_swap_high directives controls the replacement of cache objects stored on disk. The values are in percentage (%) of the cache size (i.e.sum of all the cache_dir sizes).

I have set the following configurationg for the directives in squid.conf

cache_swap_low  60

cache_swap_high 65

So, until and unless disk usage is below the 60 %, replacement does not take place and, it begins only when it is above the low water mark. Replacement is more aggressive when disk utilization is close to the high water mark.

This could help in replacing the stale cache records as well.