A Web cache (or HTTP cache) is a system for optimizing the World Wide Web. It is implemented both client-side and server-side. The caching of multimedia and other files can result in less overall delay when browsing the Web.[1][2]
A forward cache is a cache outside the web server's network, e.g. in the client's web browser, in an ISP, or within a corporate network.[3] A network-aware forward cache only caches heavily accessed items.[4] A proxy server sitting between the client and web server can evaluate HTTP headers and choose whether to store web content.
A reverse cache sits in front of one or more web servers, accelerating requests from the Internet and reducing peak server load. This is usually a content delivery network (CDN) that retains copies of web content at various points throughout a network.
HTTP optionsedit
The Hypertext Transfer Protocol (HTTP) defines three basic mechanisms for controlling caches: freshness, validation, and invalidation.[5] This is specified in the header of HTTP response messages from the server.
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. The ETag (entity tag) mechanism also allows for both strong and weak validation.
Invalidation is usually a side effect of another request that passes through the cache. For example, if a URL associated with a cached response subsequently gets a POST, PUT or DELETE request, the cached response will be invalidated. Many CDNs and manufacturers of network equipment have replaced this standard HTTP cache control with dynamic caching.
^Fountis, Yorgos (4 May 2017). "How does the browser cache work?".
^Messaoud, S.; Youssef, H. (2009). "An analytical model for the performance evaluation of stack-based Web cache replacement algorithms". International Journal of Communication Systems. 23: 1–22. doi:10.1002/dac.1036. S2CID 46507769.
^Shinder, Thomas (2 September 2008). . ISA Server. TechGenix Ltd. Archived from the original on 23 July 2011. Retrieved 27 February 2011.
^Erman, Jeffrey; Gerber, Alexandre; Hajiaghayi, Mohammad T.; Pei, Dan; Spatscheck, Oliver (2008). (PDF). AT&T Labs: 291–300. CiteSeerX10.1.1.159.1786. Archived from the original (PDF) on 1 April 2011. Retrieved 11 March 2019.
^Kelly, Mike; Hausenblas, Michael. (PDF). WS-REST. p. 20. Archived from the original (PDF) on 10 July 2010. Retrieved 14 June 2013.
Further readingedit
Ari Luotonen, Web Proxy Servers (Prentice Hall, 1997) ISBN0-13-680612-0
Duane Wessels, Web Caching (O'Reilly and Associates, 2001). ISBN1-56592-536-X
Michael Rabinovich and Oliver Spatschak, Web Caching and Replication (Addison Wesley, 2001). ISBN0-201-61570-3
April 12, 2024
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A Web cache or HTTP cache is a system for optimizing the World Wide Web It is implemented both client side and server side The caching of multimedia and other files can result in less overall delay when browsing the Web 1 2 Contents 1 Parts of the system 1 1 Forward and reverse 1 2 HTTP options 2 Legality 3 Server side software 4 See also 5 References 6 Further readingParts of the system editForward and reverse edit A forward cache is a cache outside the web server s network e g in the client s web browser in an ISP or within a corporate network 3 A network aware forward cache only caches heavily accessed items 4 A proxy server sitting between the client and web server can evaluate HTTP headers and choose whether to store web content A reverse cache sits in front of one or more web servers accelerating requests from the Internet and reducing peak server load This is usually a content delivery network CDN that retains copies of web content at various points throughout a network HTTP options edit The Hypertext Transfer Protocol HTTP defines three basic mechanisms for controlling caches freshness validation and invalidation 5 This is specified in the header of HTTP response messages from the server 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 The ETag entity tag mechanism also allows for both strong and weak validation Invalidation is usually a side effect of another request that passes through the cache For example if a URL associated with a cached response subsequently gets a POST PUT or DELETE request the cached response will be invalidated Many CDNs and manufacturers of network equipment have replaced this standard HTTP cache control with dynamic caching Legality editIn 1998 the DMCA added rules to the United States Code 17 U S C 512 that exempts system operators from copyright liability for the purposes of caching Server side software editThis is a list of server side web caching software Name Operating system Forwardmode Reversemode LicenseWindows Unix like OtherApache HTTP Server Yes OS X Linux Unix FreeBSD Solaris Novell NetWare OS 2 TPF OpenVMS eComStation Yes Apache 2 0aiScaler Dynamic Cache Control No Linux No ProprietaryApplianSys CACHEbox No Linux No ProprietaryBlue Coat ProxySG No No SGOS Yes Yes ProprietaryNginx Yes Linux BSD OS X Solaris AIX HP UX Yes Yes Yes 2 clause BSD likeMicrosoft Forefront Threat Management Gateway Yes No No Yes Yes ProprietaryPolipo Yes OS X Linux OpenWrt FreeBSD Yes Yes MIT LicenseSquid Yes Linux Yes Yes GPLTraffic Server Linux Yes Yes Apache 2 0Untangle No Linux No Yes Yes ProprietaryVarnish No Linux No Needs a VMOD Yes BSDWinGate Yes No No Yes Yes Proprietary Free for 8 users Nuster No Linux No Yes Yes GPLMcAfee Web Gateway No McAfee Linux Operating System No Yes Yes ProprietarySee also editInterPlanetary File System makes web caches redundant Cache Discovery Protocol Cache manifest in HTML5 Content delivery network Harvest project Proxy server Web accelerator Search engine cacheReferences edit Fountis Yorgos 4 May 2017 How does the browser cache work Messaoud S Youssef H 2009 An analytical model for the performance evaluation of stack based Web cache replacement algorithms International Journal of Communication Systems 23 1 22 doi 10 1002 dac 1036 S2CID 46507769 Shinder Thomas 2 September 2008 Understanding Web Caching Concepts for the ISA Firewall ISA Server TechGenix Ltd Archived from the original on 23 July 2011 Retrieved 27 February 2011 Erman Jeffrey Gerber Alexandre Hajiaghayi Mohammad T Pei Dan Spatscheck Oliver 2008 Network Aware Forward Caching PDF AT amp T Labs 291 300 CiteSeerX 10 1 1 159 1786 Archived from the original PDF on 1 April 2011 Retrieved 11 March 2019 Kelly Mike Hausenblas Michael Using HTTP Link Header for Gateway Cache Invalidation PDF WS REST p 20 Archived from the original PDF on 10 July 2010 Retrieved 14 June 2013 Further reading editAri Luotonen Web Proxy Servers Prentice Hall 1997 ISBN 0 13 680612 0 Duane Wessels Web Caching O Reilly and Associates 2001 ISBN 1 56592 536 X Michael Rabinovich and Oliver Spatschak Web Caching and Replication Addison Wesley 2001 ISBN 0 201 61570 3 Retrieved from https en wikipedia org w index php title Web cache amp oldid 1218464124, wikipedia, wiki, book, books, library,
