Caching is especially important to break up flash crowds. Flash crowds occur when a sudden event (such as breaking news, a bulk email announcement, or a celebrity event) causes many people to access a web document at nearly the same time (Screenshot 7-2). The resulting redundant traffic spike can cause a catastrophic collapse of networks and web servers.

Flash crowds can overload web servers
Flash crowds can overload web servers
(Screenshot 7-2.)

When the "Starr Report" detailing Kenneth Starr's investigation of U.S. President Clinton was released to the Internet on September 11, 1998, the U.S. House of Representatives web servers received over 3 million requests per hour, 50 times the average server load. One news web site, CNN.com, reported an average of over 50,000 requests every second to its servers.

 


Hypertext Transfer Protocol (HTTP)