Murat Demirbas (University at Buffalo)
Work on theory of distributed systems abstract away from the physical-clock time and use the notion of logical clocks for ordering events in asynchronous distributed systems. Practice of distributed systems, on the other hand, employ loosely synchronized clocks using NTP in a best-effort manner without any guarantees. Recently, we introduced a third option: hybrid clocks. Hybrid clocks combine the best of logical and physical clocks; hybrid clocks are immune to the disadvantages of either while providing benefits of both. Hybrid clocks are loosely synchronized using NTP, yet they also provide guaranteed comparison conditions as in logical clocks (LC) or vector clocks (VC) even within the time synchronization uncertainty intervals of events.
In this talk, I will present two flavors of our hybrid clocks: hybrid logical clocks (HLC) and hybrid vector clocks (HVC). HLC finds applications in multiversion distributed database systems and enable efficient querying of consistent snapshots. HVC finds applications in debugging for concurrency race conditions and in lightweight causal delivery of messages. For all practical applications and deployment environments, the size of HVC remains only as a couple entries and substantially less than N, the number of nodes. I will also talk about higher-level auditability and availability primitives, detectors and correctors, that hybrid clocks enable. I will briefly talk about our recent work on a WAN version of ZooKeeper coordination service.
Murat Demirbas is an Associate Professor of Computer Science & Engineering at University at Buffalo, SUNY. Murat received his Ph.D. from The Ohio State University in 2004 and did a postdoc at the Theory of Distributed Systems Group at MIT in 2005. His research interests are in distributed and networked systems and cloud computing. Murat received an NSF CAREER award in 2008, and UB Exceptional Scholars Young Investigator Award in 2010.