ITR: System Support for Automatic and Consistent Replication of Internet Services

Duke University, Durham NC

Investigators

Abstract

This project explores two complementary techniques for addressing fundamental limitations in replicating network services. The first aspect of this proposal seeks to automatically replicate service programs and state information to allow transparent caching or replication of dynamic services. The goal of the research is to allow transparent caching or replication of dynamic services, a key step toward automatically converting unscalable service implementations into scalable ones. The second thrust of this work is to allow network services to dynamically trade replica consistency for increased system availability and performance. The TACT (Tunable Availability and Consistency Tradeoffs) toolkit allows Internet services to flexibly and dynamically choose their own availability/consistency tradeoffs. We use three consistency metrics, Numerical Error, Order Error and Staleness to capture application-specific consistency requirements of Internet services. Applications use these metrics in addition to application-specific parameters to assign a numeric value to system consistency, e.g., the percentage of user requests that must eventually be rolled back because of underlying replica inconsistency. Finally, TACT allows consistency to be specified on a per-user, client, and replica basis, enabling differentiated quality of service.