Many software components perform caching for Web
applications. Here are some examples of caching applications:
- A Web browser saves Web pages and related objects such as image and audio
files and Java applets, locally, in memory or on disk to save network time
when its user repeatedly accesses the same pages.
- A Web proxy server cache saves Web pages and related objects on a local
server, near a group of users, to reduce network access time to remote Web
servers, for example to reduce the number of times the Web servers retrieve
requested items. A Web proxy server cache also enables efficient
sharing of commonly accessed pages between multiple users.
- A Web server caches frequently retrieved pages and related objects in
memory to save disk access time when users repeatedly retrieve the same
pages.
- A database management system caches data items, which are usually held on
disk, in memory to save disk access time when repeatedly retrieving the same
data items.
All these components perform their caching independently but the overall
result is improved response times for users. In order to determine when
to refresh a cached item, the Web components (browser, proxy server, and Web
server) usually take into consideration various options including:
- The browser and server configuration options
- The contents of the HTTP headers returned with the Web pages and related
items from the Web server, in particular the expiry date information
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