Caching FTP and Gopher Documents

FTP and Gopher do not include a method for checking to see if a document is up-to-date. Therefore, the only way to optimize caching for FTP and Gopher documents is to set a Cache Refresh interval. The Cache Refresh interval is the amount of time the Proxy Server waits before retrieving the latest version of the document from the remote server. If you do not set a Cache Refresh interval, the proxy will retrieve these documents even if the versions in the cache are up-to-date.

Setting FTP and Gopher Cache Refresh Intervals

If you are setting a cache refresh interval for FTP and Gopher, choose one that you consider safe for the documents the proxy gets. For example, if you store information that rarely changes, use a high number (several days). If the data changes constantly, you will want the files to be retrieved at least every few hours. During the refresh time, you risk sending an out-of-date file to the client. If the interval is short enough (a few hours), you eliminate most of this risk while getting noticeably faster response time.

You can set the cache refresh interval for FTP and Gopher documents on either the Set Cache Specifics page or the Set Caching Configuration page. The Set Cache Specifics page allows you to configure global caching procedures, and the Set Caching Configuration page allows you to control caching procedures for specific URLs and resources. For more information on using the Set Cache Specifics page, see Setting Cache Specifics, and for more information on using the Set Caching Configuration page, see Configuring the Cache.

If your FTP and Gopher documents vary widely (some change often, others rarely), use the Set Caching Configuration page to create a separate template for each kind of document (for example, create a template with resources ftp://.*.gif) and then set a refresh interval that is appropriate for that resource.