Leveraging run time knowledge about event rates to improve memory utilization in wide area data stream filtering

The dQUOB system conceptualization of data streams as database and its SQL interface to data streams is an intuitive way for users to think about their data needs in a large scale application containing hundreds if not thousands of data streams. Experience with dQUOB has shown the need for more aggressive memory management to achieve the scalability we desire. This paper addresses the problem with a two-fold solution. The first one is replacement of the existing first-come first-served scheduling algorithm with an earliest job first algorithm which we demonstrate to yield better average service time. The second one is an introspection algorithm that sets and adapts the sizes of join windows in response to the knowledge acquired at runtime about event rates. In addition to the potential for significant improvements in memory utilization, the algorithm presented here also provides a means by which the user can reason about join window sizes. Wide area measurements demonstrate the adaptive capability required by the introspection technique.