-----------------------------------------------------------------------
TDS Seminar TDS Seminar TDS Seminar TDS Seminar TDS Seminar TDS Seminar
-----------------------------------------------------------------------

Title:   Continuous Consistency for Wide-Area Replication: 
	 Theory and Practice

Speaker: Haifeng Yu

Place:   NE43-308
Time:    1-2:30pm
Date:    June 28, 2002

Abstract:

Replication is a key approach for scaling wide-area applications and for
achieving high-performance and high-availability. However, because of
wide-area latency and potential Internet congestion/failures, consistency
overhead in a naive replication system may actually lead to degraded
overall performance and availability relative to a centralized
architecture. This duality currently limits the deployment of replicated
services across the wide area.

In this talk, I will discuss why system consistency is continuous rather
than binary for many applications, and how these applications can
significantly benefit from exploring the semantic space between strong
consistency (linearizability) and optimistic consistency.  Specifically, I
will describe the TACT continuous consistency model that allows
applications to dynamically tune replicated system consistency.  I will
also briefly discuss the TACT prototype and performance evaluation across
the Internet.

In the second part of my talk, I will explore the consistency model's
effects on system availability. In particular, I will derive a tight
availability upper bound under continuous consistency through pruned
serialization order enumeration and reduction to IP. This
protocol-independent and implementation-independent upper bound reveals the
inherent effects of continuous consistency on availability.

-----------------------------------------------------------------------