1. 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

2. Contents DOCP? Web Cache Consistency Protocol Detail Simulation Result

3. 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 ’

4. 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

5. 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

6. DOCP Architecture

7. DOCP Consistency Protocol Operation

8. 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

9. Simulation Results (1)

10. Simulation Results (2)