Database Seminar Series (2014-2015)

In contrast to queries for on-line transaction processing (OLTP) systems that typically access only a small portion of a database, on-line analytical processing (OLAP) queries may need to aggregate large portions of a database which often leads to performance issues. We have built multi-core and cloud based real-time OLAP systems utilizing a new distributed index structure for OLAP, termed distributed PDCR tree. Our system supports multiple dimension hierarchies and efficient query processing on elaborate dimension hierarchies which are central to OLAP systems. It is particularly efficient for complex OLAP queries that need to aggregate large portions of a data warehouse. Our project is partially funded by IBM and our system has won an "IBM Innovation Impact of the Year" award.

S-Store: A Streaming NewSQL System for Big Velocity Applications (Cancelled)

Nesime Tatbul is a senior research scientist at the Intel Science and Technology Center for Big Data based at MIT CSAIL. Before joining Intel Labs, she was a faculty member at the Computer Science Department of ETH Zurich. She received her B.S. and M.S. degrees in Computer Engineering from the Middle East Technical University (METU), and her M.S. and Ph.D. degrees in Computer Science from Brown University. During her graduate school years at Brown, she also worked as a research intern at the IBM Almaden Research Center, and as a consultant for the U.S. Army Research Institute of Environmental Medicine (USARIEM). Her research interests are in database systems, with a recent focus on data stream processing and distributed data management. She is the recipient of an IBM Faculty Award in 2008, a Best System Demonstration Award at the ACM SIGMOD 2005 Conference, and both the Best Poster Award and the Grand Challenge Award at the ACM DEBS 2011 Conference. She has served on the program committee for various conferences including ACM SIGMOD (as an industrial program co-chair in 2014 and as a group leader in 2011), VLDB, and IEEE ICDE (as a PC track chair for Streams, Sensor Networks, and Complex Event Processing in 2013). She has chaired a number of VLDB co-located workshops including the International Workshop on Data Management for Sensor Networks (DMSN) and the International Workshop on Business Intelligence for the Real-Time Enterprise (BIRTE). Her recent editorial duties include PVLDB (associate editor, Volume 5, 2011-2012) and ACM SIGMOD Record (associate editor, Research Surveys Column, since June 2012).

Modern Cloud and Data Center environments are based on large scale distributed storage systems. Diagosing configuration errors, software bugs and performance anomalies in such systems has become a major problem for large Web hosting sites.

As part of a larger project, which endeavors to design and prototype interactive, guided modelling for such systems I will introduce Stage-aware Anomaly Detection (SAAD), a low overhead real-time solution for detecting runtime anomalies in storage systems. SAAD is based on the key observation that most state-of-the-art storage server architectures are multi-threaded and structured as a set of modules, which we call stages.

SAAD leverages this observation to collect stage-level log summaries at runtime and to perform statistical analysis across stage instances. Stages that generate rare execution flows and/or register unusually high duration for regular flows at run-time indicate anomalies. SAAD makes two key contributions: i) limits the search space for root causes, by pinpointing specific anomalous code stages, and ii) reduces compute and storage requirements for log analysis, while preserving accuracy, through a novel technique based on log summarization.

We evaluated SAAD on three distributed storage systems: HBase, Hadoop Distributed File System (HDFS), and Cassandra. We show that, with practically zero overhead, we uncover various anomalies in real-time.

In this talk, I will present some recent work on these three activities with particular emphasis on a recent work where we propose a query-oriented system for cleaning data with oracles.  Unlike prior data cleaning techniques where the focus has largely been to correct all existing data upfront, our framework is driven by the correctness of query results, cleans data only as needed, and also permits one to augment the underlying dataset through the identification of missing tuples in the result of a query.  Incorrect/missing tuples are removed/added to the result of a query through edits that are applied to the underlying dataset, where the edits are derived by interacting with domain experts which we model as oracle crowds.   

We show that the problem of determining minimal interactions with oracle crowds to derive database edits for removing/adding incorrect/missing tuples to the result of a query is NP-hard in general and present heuristic algorithms that interact with oracle crowds to progressively clean the dataset, as needed.  I will also present recent work on temporal record linkage and integration that allows one to identify which facts are temporally related and how they can be meaningfully combined together.

Multi-tenancy and resource sharing are essential to make a Relational Database-as-a-Service (DaaS), such as Azure SQL Database, cost-effective. However, one major consequence of resource sharing is that the performance of one tenant's workload can be significantly affected by the resource demands of co-located tenants. In the SQLVM project at Microsoft Research, our approach to performance isolation in a DaaS is to isolate the key resources, such as CPU, I/O and memory, needed by the tenants' workload. The major challenge is in supporting this abstraction within a RDBMS for a wide variety of workloads and demands, without statically allocating resources, while ensuring low overheads and scaling to large numbers of tenants. Mechanisms designed in the SQLVM project are now in production and form an integral part of the Azure SQL Database Service Tiers and Performance Levels made generally available in September 2014.

More information about the project can be found at: http://research.microsoft.com/en-us/projects/sqlvm/.

Steps towards HW/SW-DB-CoDesign (PDF)