The Distributed Object Consistency Protocol Version 1.0 John Dilley, Martin Arlitt, Stephane Perret, Tai Jin Hewlett-Packard Laboratories Palo Alto, CA CoreLab, EE, KAIST Jupyung Lee

Contents DOCP? Web Cache Consistency Protocol Detail Simulation Result

DOCP? DOCP: Protocol for improving content consistency in web proxy cache servers Reduce response time & server load Extension to HTTP, replacing some of HTTP ’ s current cache control mechanism Publish/subscribe mechanism Server invalidation Improving consistency -> reduce response time & server load? In case of bad consistency,  Client side : ‘ reload ’  Content provider : ‘ disable cache ’  Web Proxy Server : ‘ client validation ’

Web Cache Consistency Consistency Model Strong consistency  Atomic, sequential, causal, Pipelined RAM Weak consistency  Delta Consistency, Eventual consistency, Loose, Periodic, Offline DOCP : guarantee ‘ Delta Consistency ’ Consistent except bounded time after a modification Low overhead

Things to Considerate Web Traffic Characterization “ 60% of objects were requested only once. ” Diversity in frequency of modification Internet Philosophy The consistency protocol must be an incremental addition to the system

DOCP Architecture

DOCP Consistency Protocol Operation

Protocol Detail Strong Point Reduce # of invalidation notification No communication between master & slave is required to release a lease Reduce communication between Master & Slave Subscription Decision – Slave Local popularity, size, last modification time, last access time Subscription Decision – Master Popularity, size, modification history, # existing subscriptions Single object share same lease value expiration time Usually days ~ weeks Expiration time : 2~5 AM

Simulation Results (1)

Simulation Results (2)