Supporting SQL-3 aggregations on grid-based data repositories

There is an increasing trends towards distributed and shared repositories for storing scientific datasets. Developing applications that retrieve and process data from such repositories involves a number of challenges. First, these data repositories store data in complex, low-level layouts, which should be abstracted from application developers. Second, as data repositories are shared resources, part of the computations on the data must be performed at a different set of machines than the ones hosting the data. Third, because of the volume of data and the amount of computations involved, parallel configurations need to be used for both hosting the data and the processing on the retrieved data. In this paper, we describe a system for executing SQL-3 queries over scientific data stored as flat-files. A relational table-based virtual view is supported on these flat-file datasets. The class of queries we consider involve data retrieval using Select and Where clauses, and processing with user-defined aggregate functions and group-bys. We use a middleware system STORM for providing much of the low-level functionality. Our compiler analyzes the SQL-3 queries and generates many of the functions required by this middleware. Our experimental results show good scalability with respect to the number of nodes as well as the dataset size.