Up-to-Date Checks

Proxy Servers increase performance by serving documents out of a local cache rather than obtaining them from the origin server. One drawback to this methodology is the potential to provide documents that are out of date.

The Proxy Server can perform a check to determine whether a document is up to date, and then refresh the cached version if it is determined that the document is old. This up-to-date check should be performed only as necessary, as frequently checking documents can decrease the overall performance of the Proxy Server.

Up-to-date checking is configured on the Set Cache Specifics page of the Caching tab. The default is to check for a new document every two hours. This information is configured in the ObjectType directive with the max-uncheck parameter.

To improve the server’s performance while ensuring that a document is up-to-date, customize up-to-date checking by determining a reasonable document lifetime in conjunction with the last-modified factor, which is discussed below.

Last-Modified Factor

The last-modified factor is used to fine-tune document up-to-date processing. This factor helps determine the likelihood that a document will change based on the previous changes that have been noted.

The last-modified factor is a fraction between .02 and 1.0. It is multiplied by the interval between a document’s actual last modification and the time the last up-to-date check was performed on the document. The resulting number is compared with the time since the last up-to-date check. If the number is smaller than the time interval, the document has not expired. If, however, it is larger than the time interval, then the document has expired and a new version is obtained from the origin server.

The last-modified factor enables you to ensure that recently changed documents are checked more often than old documents.

You should set a last-modified factor between 0.1 and 0.2.