Web Proxy Caching

Web proxy caching stores copies of frequently accessed Web objects (such as documents, images, and articles) close to users and serves this information to them. Internet users get their information faster, and Internet bandwidth is freed for other tasks.

Internet users direct their requests to Web servers all over the Internet. For a caching server to serve these requests, it must act as a Web proxy server. A Web proxy server receives user requests for Web objects and either serves the requests or forwards them to the origin server (the Web server that contains the original copy of the requested information).

Content Gateway supports both transparent proxy deployment, in which the user's client software (typically a browser) is unaware that it is communicating with a proxy, and explicit proxy deployment, in which the user's client software is configured to send requests directly to the proxy.

Cache requests

Related topics:

Ensuring cached object freshness

Scheduling updates to local cache content

Pinning content in the cache

To cache or not to cache?

Caching HTTP objects

Forcing object caching

Caching HTTP alternates

Caching FTP objects

The following overview illustrates how Content Gateway serves a user request.

Content Gateway receives a user request for a Web object.

Using the Web address, the proxy tries to locate the requested object in its object store (cache).

If the object is in the cache, the proxy checks to see if the object is fresh enough to serve (see Ensuring cached object freshness). If the object is fresh, the proxy serves it to the user as a cache hit.

If the data in the cache is stale, the proxy connects to the origin server and asks if the object is still fresh (a revalidation). If the object is still fresh, the proxy sends the cached copy to the user.

If the object is not in the cache (a cache miss) or the server indicates that the cached copy is no longer valid, the proxy obtains the object from the origin server, simultaneously streaming it to the user and the cache. Subsequent requests for the object will be served faster because the object will come directly from the cache.

Content Gateway can store and serve Java applets, JavaScript programs, VBScripts, and other executable objects from its cache according to the freshness and cacheability rules for HTTP objects. Content Gateway does not execute the applets, scripts, or programs. These objects run only when the client system that sent the request loads them.

Content Gateway does not store partial documents in the cache. Should a client disconnect while an HTTP or FTP download is underway, Content Gateway continues the download for up to 10 seconds after the disconnect. If the transfer completes successfully, Content Gateway stores the object in the cache. If the download does not complete, Content Gateway disconnects from the origin server and deletes the object from the cache.