Anomaly-free incremental output in stream processing

Abstract

Continuous queries enable alerts, predictions, and early warning in various domains such as health care, business process monitoring, financial applications, and environment protection. Currently, the consistency of the result cannot be assessed by the application, since only the query processor has enough internal information to determine when the output has reached a consistent state. To our knowledge, this is the first paper that addresses the problem of consistency under the assumptions and constraints of a continuous query model. In addition to defining an appropriate consistency notion, we propose techniques for guaranteeing consistency. We implemented the proposed techniques in our existing stream engine, and we report on the characteristics of the observed performance. As we show, these methods are practical as they impose only a small overhead on the system. © 2008 ACM.