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)