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Web cache
 
 
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Web caching is the caching
Cache

In computer science, a cache is a collection of data duplicating original values stored elsewhere or computed earlier, where the original data is expensive to fetch or to compute, compared to the cost of reading the cache....
 of web document
Web document

Web document is a similar concept to web page, except it is a broader termwith the following distinctions: ...
s (e.g., HTML pages, images
Digital image

A digital image is a representation of a two-dimensional using ones and zeros . Depending on whether or not the is fixed, it may be of vector graphics or raster graphics type....
) in order to reduce bandwidth
Bandwidth (computing)

In computer networking and computer science, digital bandwidth, network bandwidth or just bandwidth is a measure of available or consumed data communication resources expressed in bit/s or multiples of it ....
 usage, server
Web server

The term web server can mean one of two things:# A computer program that is responsible for accepting Hypertext Transfer Protocol requests from clients , and Server them HTTP responses along with optional data contents, which usually are web pages such as Hypertext Markup Language documents and linked objects ....
 load, and perceived lag
Lag

In computing and especially computer networks, lag is a term used where the computer freezes and then continues some time later when an action is performed, for example clicking a mouse button....
. A web cache stores copies of documents passing through it; subsequent requests may be satisfied from the cache if certain conditions are met.

It is not to be confused with a web archive, a site that keeps old versions of web pages

caches can be deployed in a variety of ways.






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Web caching is the caching
Cache

In computer science, a cache is a collection of data duplicating original values stored elsewhere or computed earlier, where the original data is expensive to fetch or to compute, compared to the cost of reading the cache....
 of web document
Web document

Web document is a similar concept to web page, except it is a broader termwith the following distinctions: ...
s (e.g., HTML pages, images
Digital image

A digital image is a representation of a two-dimensional using ones and zeros . Depending on whether or not the is fixed, it may be of vector graphics or raster graphics type....
) in order to reduce bandwidth
Bandwidth (computing)

In computer networking and computer science, digital bandwidth, network bandwidth or just bandwidth is a measure of available or consumed data communication resources expressed in bit/s or multiples of it ....
 usage, server
Web server

The term web server can mean one of two things:# A computer program that is responsible for accepting Hypertext Transfer Protocol requests from clients , and Server them HTTP responses along with optional data contents, which usually are web pages such as Hypertext Markup Language documents and linked objects ....
 load, and perceived lag
Lag

In computing and especially computer networks, lag is a term used where the computer freezes and then continues some time later when an action is performed, for example clicking a mouse button....
. A web cache stores copies of documents passing through it; subsequent requests may be satisfied from the cache if certain conditions are met.

It is not to be confused with a web archive, a site that keeps old versions of web pages

Types of Web caches

Web caches can be deployed in a variety of ways. User agent
User agent

A user agent is the client application used with a particular network protocol; the phrase is most commonly used in reference to those which access the World Wide Web, but other systems such as Session Initiation Protocol use the term user agent to refer to the user's phone....
 caches, such as those in web browser
Web browser

A Web browser is a application software which enables a user to display and interact with text, images, videos, music, games and other information typically located on a Web page at a website on the World Wide Web or a local area network....
s, are private caches, operating on behalf of a single user. Intermediaries can also implement shared caches that serve more than one person.

Proxy
Proxy server

In computer networks, a proxy server is a server that acts as a go-between for requests from client seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource, available from a different server....
 caches, also known as forward proxy caches, are usually deployed by internet service provider
Internet service provider

An Internet service provider is a company that offers its customers access to the Internet. The ISP connects to its customers using a data transmission technology appropriate for delivering Internet Protocol datagrams, such as dial-up, DSL, cable modem or dedicated high-speed interconnects....
s, schools and corporations to save bandwidth. Interception proxy caches (sometimes called "transparent caches") are a variant that doesn't require clients to be explicitly configured to use them.

Gateway
Gateway (telecommunications)

In telecommunications, the term gateway has the following meaning:*In a communications network, a network node equipped for interfacing with another network that uses different protocols....
 caches, sometimes known as reverse proxy
Reverse proxy

A reverse proxy or surrogate is a proxy server that is installed within the neighborhood of one or more Server s. Typically, reverse proxies are used in front of Web servers....
 caches, surrogate caches, or web accelerator
Web accelerator

A web accelerator is a proxy server that reduces web site access times. They can be a self-contained hardware appliance or installable software....
s, operate on behalf of the origin server, and to clients are indistinguishable from it. A number of gateway
Gateway (telecommunications)

In telecommunications, the term gateway has the following meaning:*In a communications network, a network node equipped for interfacing with another network that uses different protocols....
 caches can work together to implement a Content Delivery Network
Content Delivery Network

A content delivery network or content distribution network is a system of computers Computer network together across the Internet that cooperate transparently to deliver content to end users, most often for the purpose of improving performance, scalability, and cost efficiency....
.

Intermediaries that cache often perform other duties, such as user authentication
Authentication

Authentication is the act of establishing or confirming something as authentic, that is, that claims made by or about the subject are true....
 and content filtering
Content-control software

Content-control software, also known as censorware or web filtering software, is a term for Computer software designed and optimized for controlling what content is permitted to a reader, especially when it is used to restrict material delivered over the World Wide Web....
. Multiple caches can also be coordinated using peering protocols like Internet Cache Protocol
Internet Cache Protocol

The Internet Cache Protocol is a protocol used for coordinating web caches. Its purpose is to find out the most appropriate location to retrieve a requested object from in the situation where multiple caches are in use at a single site....
 and HTCP
Hypertext caching protocol

Hypertext Caching Protocol is used for discovering [] caches and cached data, managing sets of HTTP caches and monitoring cache activity. It permits full request and response headers to be used in cache management and expands the domain of cache management to include monitoring a remote cache's additions and deletions, requesting immediate d...
.

Controlling Web caches

HTTP defines three basic mechanisms for controlling caches: freshness, validation and invalidation.

  • Freshness allows a response to be used without re-checking it on the origin server, and can be controlled by both the server and the client. For example, the Expires response header gives a date when the document becomes stale, and the Cache-Control: max-age directive tells the cache how many seconds the response is fresh for.
  • Validation can be used to check whether a cached response is still good after it becomes stale. For example, if the response has a Last-Modified header, a cache can make a conditional request using the If-Modified-Since header to see if it has changed.
  • Invalidation is usually a side effect of another request that passes through the cache. For example, if URL associated with a cached response subsequently gets a POST, PUT or DELETE request, the cached response will be invalidated.


In 1998 the DMCA added rules to the United States Code
United States Code

The United States Code is a compilation and codification of the general and permanent federal law of the United States. ...
 () that relieves system operators from copyright liability for the purposes of caching.

Web cache software

  • Dijjer
    Dijjer

    Dijjer is a peer-to-peer web cache. It is "pure" P2P because it relies on the computers of those using it, and is almost completely decentralization....
  • most proxy server software
    Proxy server

    In computer networks, a proxy server is a server that acts as a go-between for requests from client seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource, available from a different server....
     also caches content


See also

  • Proxy server
    Proxy server

    In computer networks, a proxy server is a server that acts as a go-between for requests from client seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource, available from a different server....


External links