Caching

Production web sites often improve their perceived response times by the extensive use of caching. Many processes throughout a web site's network establish caches, and understanding their roles becomes important when predicting performance. Caches clearly have the most impact when they are close to the user. Browsers use caching extensively by putting images and other content into both memory caches as well as caches on the local disk. This dramatically shortens the interval between a user 's click on a link or button and the complete display of the resulting page. (This helpful function can cause headaches when testing dynamic content, as the browser may display a cached copy instead of getting new content from the server.) The browser periodically makes a special request to the server to see if the content has changed since the copy was put in the cache, and only if that is true does the browser request a new copy.).

As discussed above, caching proxy servers, located close to the edge of your network, not only speed up response times to your users, but also decrease the load on your servers and network. If static content makes up a large fraction of your web site's total content, setting up caching reverse proxy servers greatly increases your web site's total throughput and decreases response time. (Some HTTP servers also cache static content.) Some very popular sites contract with other enterprises to cache their content. The data is pushed to caches located within a large ISP's own network, and the requests then go to these caching machines. This technique proves especially useful for graphics-heavy web sites.