Performance debugging of geo-distributed storage systems

Dejan Kostic - Professor of Internetworking at the KTH Royal Institute of Technology
Data Science

Date: March 1st 2016
Location: Eurecom - Eurecom

Title: Performance debugging of geo-distributed storage systems Abstract: Modern distributed systems are geo-distributed for reasons of increased performance, reliability, and survivability. At the heart of many such systems, e.g., the widely used Cassandra and MongoDB data stores, is an algorithm for choosing a closest set of replicas to service a client request. Dynamically changing network conditions pose a significant problem, with suboptimal replica choices resulting in reduced performance due to increase response latency. In this talk I will present GeoPerf, a tool that tries to automate the process of systematically testing the performance of replica selection algorithms for geo-distributed storage systems. At the core of our approach is a novel technique that combines symbolic execution and lightweight modeling to generate a set of inputs that can expose weaknesses in replica selection. As part of our evaluation, we analyzed network round trip times between geographically distributed regions of the Amazon EC2 cloud, and compute how often the order of nearest replicas changed per day from any given region's perspective. We tested Cassandra and MongoDB using our tool, and found bugs in each of these systems. Finally, we use our collected Amazon EC2 latency traces to study the behavior of these buggy replica selection algorithms under realistic circumstances. We find that significant time was lost due to programming errors. For example due to the bug in Cassandra, the median wasted time for 10% of all requests is above 50 ms. Biography : Dejan Kostic is a Professor of Internetworking at the KTH Royal Institute of Technology, where he is the head of the Network Systems Laboratory. He is also associated with the Decisions, Networks and Analytics (DNA) Laboratory of the Swedish Institute of Computer Science (SICS). His research interests include Distributed Systems, Computer Networks, Operating Systems, and Mobile Computing. Dejan Kostic obtained his Ph.D. in Computer Science at the Duke University. He spent the last two years of his studies and a brief stay as a postdoctoral scholar at the University of California, San Diego. He received his Master of Science degree in Computer Science from the University of Texas at Dallas, and his Bachelor of Science degree in Computer Engineering and Information Technology from the University of Belgrade (ETF), Serbia. From 2006 until 2012 he worked as a tenure-track Assistant Professor at the School of Computer and Communications Sciences at EPFL (Ecole Polytechnique Federale de Lausanne), Switzerland. In 2010, he received a European Research Council (ERC) Starting Investigator Award. From 2012 until June 2014, he worked at the IMDEA Networks Institute (Madrid, Spain) as a Research Associate Professor with tenure. He is a Professor of Internetworking at KTH since April 2014

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