Refresh patterns determine what is saved and served from the cache.
Ideally, you would want your squid to follow the directions of the Web servers serving the content to determine what is cacheable and for how long.
These directions are set as HTTP headers that are processed and understood by Squid.
Unfortunately, the directions given by most servers are the Web servers’ defaults, and do not produce significant bandwidth savings.
Squid Refresh Patterns - Anti-Virus
Squid Refresh Patterns - Facebook
Squid Refresh Patterns - Microsoft
Squid Refresh Patterns - Ubuntu
Squid Refresh Patterns - YouTube
Squid Refresh Patterns - Catch-All
Refresh patterns are of the format:
refresh_pattern [-i] regex min percent max [options]
where min and max are time values in minutes and percent is a percentage figure. The options are:
Consult your configuration file to see which of these options are available in your version of Squid.
Refresh patterns are effective if there is no expire header from the origin server, or your refresh pattern has an override-expire option. Example:
refresh_pattern -i .gif$ 1440 20% 10080.
This says:
For objects that scarcely change under the same file name, such as video, images, sound, executables, and archives, you can modify the refresh pattern to consider them fresh on your Squid for a longer time, increasing the probability of having hits. For example, you could modify our refresh pattern above to:
refresh_pattern ^ftp: 1440 20% 10080 refresh_pattern ^gopher: 1440 0% 1440 refresh_pattern -i .(gif|png|jpg|jpeg|ico)$ 10080 90% 43200 override-expire ignore-no-cache ignore-no-store ignore-private refresh_pattern -i .(iso|avi|wav|mp3|mp4|mpeg|swf|flv|x-flv)$ 43200 90% 432000 override-expire ignore-no-cache ignore-no-store ignore-private refresh_pattern -i .(deb|rpm|exe|zip|tar|tgz|ram|rar|bin|ppt|doc|tiff)$ 10080 90% 43200 override-expire ignore-no-cache ignore-no-store ignore-private refresh_pattern -i .index.(html|htm)$ 0 40% 10080 refresh_pattern -i .(html|htm|css|js)$ 1440 40% 40320 refresh_pattern . 0 40% 40320
Sometimes, for no good reason, at least from our perspective, origin servers, such as youtube.com, do everything to make it difficult or impossible for you to cache content. The options above should help you to overcome some of these limitations.
Refresh patterns are matched against all requests in order from the top until there is a matching rule.
The last rule is a catch-all and will match any request that is not satisfied by any of the rules above it.
There are normally separate catch-all default rules for other protocols like FTP and gopher at the very top of the list so as to exempt those protocols from the patterns below them.
By default, Squid will not cache dynamic content.
Dynamic content is determined by matching against either “cgi-bin” or “?”.
This feature used to be activated via the “hierarchy_stoplist” and “cache deny” settings in older versions of Squid.
In recent versions, starting with 3.1, this feature is activated via a refresh pattern such as refresh_pattern (/cgi-bin/|?) 0 0% 0.
This enables you to specify sites that serve dynamic content that could be made cacheable in bypass rules. For example, you could set up a refresh pattern such as:
refresh_pattern -i movies.com/.* 10080 90% 43200 refresh_pattern (/cgi-bin/|?) 0 0% 0
Then, even if content from movies.com is served with “?” in their URL, the content will still be cached if all other conditions are met.
For the older versions of Squid, you will have to define an access control list (ACL) for the content providers you wish to make exceptions for, and use cache accept to exempt it before the cache deny rule. The following example is from the Squid wiki:
# Let the client's favourite video site through acl youtube dstdomain .youtube.com cache allow youtube # Now stop other dynamic stuff being cached hierarchy_stoplist cgi-bin ? acl QUERY urlpath_regex cgi-bin ? cache deny QUERY
Squid makes a lot of DNS requests, one dns request for each http request.
Install a caching DNS server on your server and have Squid use it so as to cut down on your DNS requests. This how-to may be helpful.
For monitoring and log analysis to determine the performance of your Squid, you can use squid3-client and calamaris.