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LAN Cache
Networking
Hit ratio of web cache (cache at proxy) can be increased considerably by replacing centralized proxy cache system by decentralized LAN cache system. Also, scalability of caching system increases due to distributed caching and distributed querying. 1.Many static and/or dynamic web pages/objects are cached at proxy 2.Proxy hit ratios tend to decrease as the demand and supply of Web contents are becoming more diverse 3.Significant document duplications among a proxy and its clients 4.Centralized proxy caching is not scalable Need of LAN Caching In normal browser-proxy system, each browser has its own cache which holds recent requests of that particular client; also proxy has cache which holds recent requests from any of the clients connected to the LAN In the current system, there may be multiple copies of the same data object at different browsers and also at proxy which is waste of resources Also, client requests proxy if it does not have data in its local cache even if some other client has the same data in its cache, so all the searching and data transfer operations are performed at the proxy only.
Proxy maintains “Browser Index file” – Index of data objects of all client’s cache For each object, store list of running nodes and down nodes which have cached object On client A when a user makes a request 1.Search the local browser's cache. If its a miss, 2.Proxy searches its own cache. If its a miss, 1.Proxy searches “Browser Index file”. If its a hit; data present at client P, 2.Proxy increments the ACCESSED count of the object. If ACCESSED > THRESHOLD_PROXY, copy object at proxy cache as well. i.Proxy requests client P to send data on its behalf OR ii.Proxy obtains data from P and sends it to the client A. 3.If it's a miss, request is passed on to the Web (WAN). When Web (WAN) is used to complete a client’s request a)Data is cached only at client’s browser’s cache b)Entry is made in the “Browser Index file” at the proxy When a client starts LanCache service a)Client informs proxy that it is now available. b)Proxy updates its “Browser Index file” When a client stops LanCache service a)Client informs proxy that it is now unavailable. b)Proxy updates its “Browser Index file” Client decides to delete an object from its cache a)Client informs proxy that object is now unavailable. b)Proxy updates its “Browser Index file” Client crashes a)Proxy needs to poll all clients to verify status of client
1.Building a Large and Efficient Hybrid Peer-to-Peer Internet Caching System IEEE TRANSACTIONS ON KNOWLEDGE AND DATA ENGINEERING, VOL. 16, NO. 6, JUNE 2004 Li Xiao, Member, IEEE, Xiaodong Zhang, Senior Member, IEEE, Artur Andrzejak, and Songqing Chen, Student Member, IEEE 2.Squirrel: A decentralized peer-to-peer web cache 21th ACM Symposium on Principles of Distributed Computing (PODC 2002) Sitaram Iyer, Rice University Antony Rowstron, Microsoft Research Peter Druschel, Rice University 3.A Scalable Content-Addressable Network SIGCOMM’01, August 27-31, 2001, San Diego, California, USA. Sylvia Ratnasamy (1, 2), Paul Francis (2), Mark Handley (2), Richard Karp (1,2), Scott Shenker (2) (1): Dept. of Electrical Eng. & Comp. Sci. University of California, Berkeley Berkeley, CA, USA (2): ACIRI AT&T Center for Internet Research at ICSI Berkeley, CA, USA 4.Application-Level Document Caching in the Internet Boston University, Computer Science Department (Technical Report) Azer Bestavros, Robert L. Carter, Mark E. Crovella, Carlos R. Cunha, Abdelsalam Heddaya, Sulaiman A. Mirdad 5.LAN-Based Web Caching for Accelerated Web Access Philip Romine Director, Cachelink Development Mangosoft, Inc