Last time, I discussed Port80 Software's Web content compression tools (see editorial links below). Port80 recently conducted the first survey of the use of expiration-based cache control by Fortune 1000 companies.

Expiration-based cache control eliminates unnecessary resource requests by marking up Web pages so that caching proxies and the browser know when to reload data from a site and when to load the data from a local cache. The result of implementing expiration-based cache control is that Web content is served faster and both server and network bandwidth are reduced by removing unnecessary requests.

In the "Port80 Top 1000 Cache Control Survey," the company found that 21.1% (sample size 1,000 ... natch) of the Fortune 1000 Web sites are currently using expiration-based cache control to reduce server requests.

The methodology used was to download each site's home page with supporting files and then analyze the response headers to determine which of the pages' objects were cacheable, that is, all external resources that are not markup. They also checked what percentage of those cacheable objects included explicit expiration-based cache control headers.

What I found surprising was that of those sites that were found to use expiration-based cache control only 28.1% of the total home page files included explicit cache control directives. In other words, the sites' use of expiration-based cache control was incomplete. Seems odd that you'd go to the trouble of adding caching control to your Web site but not really make it pay off as much as it could.

Port80 provides a tool for examining both the caching performance of any of the Fortune 1000 as well as testing any other site you please.

It won't surprise you that Port80 has a solution to the issue of caching but we'll keep that for the next issue.

Mark Gibbs is a consultant, author, journalist, columnist and blogger.