194 CHAPTER 12: P RELOADING CONTENTIntroduction The Preload Content Feature enables the administrator and otherauthorized users to preload required sites onto the Webcache before theyare requested. These preloads can be done manually or run on a scheduleoutside working hours and enable you to store content in the Webcachethat you know will be required by a client’s Web browser.Preloading content will not cache dynamic Web pages such as thoseserved from Web searches or those pages disallowed by use of arobots.txt file.As part of these preloads, the administrator may also specify a contentlifetime for the Web pages that are preloaded. The Content Lifetimeensures that the content, once preloaded is guaranteed to be a cache hitfor a period of time. The lifetime rules will override any server HTTP cachecontrol directives (excluding dynamic content and pages marked‘no-cache’ by the Web server), and remove the need for any freshnesschecks by the Webcache itself.Cache Control settings take precedence over Content Preload. If a site ismarked as Never Cache in Cache Control then it will never be cachedeven if Content Preload gives it a Cache Lifetime.Advantages andDisadvantages ofPreloading ContentPreloading content results in a faster response time for the clients of theWebcache and less activity across your Internet connection. Any requestmade for a Web page within its Content Lifetime will not result in anytraffic external to your network as the Webcache is able to serve the pagefrom the cached content. Additionally, preload tasks can be scheduledwhen your network is quietest, for example by using spare WANbandwidth at night.When preloading content, care needs to be taken with the ContentLifetime that is set. A site that is accessed within its Content Lifetime willbe served from the Webcache without reference to the origin server.Preloading a daily news Web site with a Content Lifetime of one weekwill result in your users seeing the same day’s news for the seven dayperiod. Even pinning the content for a day will result in your users missingout on any news flashes and possibly seeing the previous days news if thecontent is preloaded before the site is refreshed.In summary, preloading content: Saves the WAN bandwidth of your network.dua1611-5aaa04.book Page 194 Friday, November 29, 2002 8:56 PM
