It is arguably the most important function of a web proxy at least as far as performance is concerned and that’s on-demand caching.  That is documents or web pages which are cached upon request by a client or application.    It’s important to remember that a document can only be cached if it has actually been requested by a user.  Without a request, it will not be cached and indeed the proxy server will not even be aware of it’s existence.

This is a different method than using a replication model which is typically used to distribute data and updates.   This is more often used on larger, busier networks where data can be replicated onto specific servers, this method is also known as mirroring and also useful for sharing over the internet.     One of the most common examples for mirroring is when a large software package is being distributed instead of a single server being responsible, multiple duplicates are replicated onto different servers.

One of the best ways to facilitate performance increases is to use a method called round-robin DNS.  This involves mapping a single host name to multiple physical servers.  These servers must be assigned separate IP and physical addresses and their addresses distributed evenly among the clients requesting the software.    When using the DNs method, the clients will be unaware of the existence of multiple servers because they will appear as a single logical server.

Most of the caching solutions used by proxies are centred around removing the load on a specific server.  However when a proxy caches resources locally without mirroring or replication then it’s still the single server which is responsible.    The physical loads doesn’t decrease however it does reduce the number of network requests that the server has to implement.   This also reduces the number of name requests that the server makes which can also introduce some levels of latency.

Having caching enabled can reduce the speed of the server responses significantly.  However this does depend largely on the sort of requests that are made, imagine a proxy used specifically to obtain a Czech IP Address and directly download a specific resource.  Caching that resource locally would improve the speed significantly as long as the content didn’t change much, however this would be different for sites which stream audio or video and contained large amounts of multimedia content.

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