web_caching - Today CSCI 5105 Foundations of Modern...

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1 CSCI 5105 Spring 2006 Copyright © 2005 Abhishek Chandra CSCI 5105 Foundations of Modern Operating Systems Instructor:Abhishek Chandra CSCI 5105 Spring 2006 Copyright © 2005 Abhishek Chandra 2 Today Web Caching Replica Placement Update Propagation Eventual Consistency CSCI 5105 Spring 2006 Copyright © 2005 Abhishek Chandra 3 Web Caching Web server is primary replica Web pages are cached at: Server replicas Client browsers Proxy caches Content-distributions networks (CDNs) Where are these replicas placed? How are updates sent to different replicas? CSCI 5105 Spring 2006 Copyright © 2005 Abhishek Chandra 4 Replica Placement Permanent replicas: Server replication, mirroring Server-initiated replicas: Push caching, CDNs Client-initiated replicas: Proxies, client caches
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2 CSCI 5105 Spring 2006 Copyright © 2005 Abhishek Chandra 5 Permanent Replicas Server replication Multiple servers hosting a Web site Typically hosted on a LAN/cluster Requests are distributed among the servers: Front-end load balancer, Dynamic DNS mapping Mirroring Popular Websites have multiple fixed servers Users select one of the mirror sites E.g.: http://www.kernel.org/mirrors CSCI 5105 Spring 2006 Copyright © 2005 Abhishek Chandra 6 Server-Initiated Replicas Servers are responsible for pushing updates to
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web_caching - Today CSCI 5105 Foundations of Modern...

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