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Focus on Faculty Talk: Christopher Stewart

Thursday, November 12, 2015, 4:00 pm
Christopher Stewart
480 Dreese Labs
2015 Neil Ave
Columbus, OH 43210

Efficient and Sustainable Models for the Next Generations of Internet Services


For decades, Denard Scaling produced smaller, faster transistors without increasing power density.  Faster transistors led to faster processors that sparked a virtuous cycle of software development.  However, Denard Scaling will soon reach its limits. In my group, we are studying models for software design and management in the post-Denard era. Our work targets Internet services where response time affects profit.  Service level objectives are widely used to align response time and business costs. Zoolander is a model-driven middleware for key-value stores that parallelizes lookups cost effectively, trading costly service-level violations for less costly replication.  When systems-level management, e.g., replication, does not suffice to meet SLOs, approximation may be an answer.  Ubora measures the effect of approximation on the quality of answers produced by a service.  Consider the OpenEphyra question-answering system, a mature query execution may yield the same answer as a partial execution because of redundancy within the data. We’ve used OpenEphyra in Jeopardy competitions with 7th and 8th graders, as a part of our outreach efforts.  We used Ubora to control approximation during the competitions.  Early outcomes suggest that approximation can significantly reduce response time without degrading answer quality too much (i.e., our system still wins!).


Dr. Stewart is an assistant professor in the computer science and engineering department at The Ohio State University.  He leads the ReRout Lab where high-impact research produces novel systems and diverse expertise that broadens computer science, i.e., research that reaches out.  Dr. Stewart’s research spans all aspects of Internet services from server hardware and datacenters to operating systems and middleware to novel emerging workloads.  His recent research has focused on 1) cost/energy efficiency for infrastructure services and 2) powering services with clean energy.  Dr. Stewart is a recipient of the prestigious NSF Career Award.  He has co-authored award papers at two international conferences and served as a founding member of the IEEE Special Technical Committee on Sustainable Computing.