Tools for Expiration-Based Cache Control
Port80 Software conducts periodic surveys of Fortune 1000 corporate Web sites to discover if they are using expiration-based cache control policies for server request reduction and Web application acceleration.
This survey is conducted between the first and fifteenth of a selected month and queries a list of 1000 leading global corporations' main corporate Web sites (e.g. www.corporation.com). Port80 Software queries this list of sites via a standard HTTP 1.1 GET request*. The target file is the resolved home page (after any redirects) and its supporting elements, including frames, entry redirect pages, includes, graphics, and other files. The HTTP headers and any associated entity bodies returned with the response are saved. The HTTP headers are then analyzed for the expiry header data to determine the number of files that contain explicit expiration-based HTTP cache control directives.
Further analysis of the data allows for savings figures to be generated for the number and/or percentage of bytes saved and transmission speed improvement gained by using cache control. These figures attempt to gauge the impact that cache control policies would have on a repeat visit by a user with a Web browser enabled for local caching.
Real-time queries of the survey list or of any Web site using Port80 Software's "cache check" tool may provide different results on bytes and cache control speed and savings from those published by Port80 Software.
* HTTP 1.0 GET requests were used for the January 2003-August 2003 Surveys, and HTTP 1.1 GET requests were used for all surveys after September 2003.