Query Processing using Negative Tuples in Stream Query Engines

The concept of Negative Tuples (or delete tuples) has been adopted widely in data stream management systems to evaluate continuous sliding-window queries incrementally . The main idea is to produce a negative tuple for each expired tuple from the sliding window. Thus, various query operators can update their state based on the expired tuples. Negative tuples avoid the non-deterministic output delays that result from the commonly used input-triggered approach. However, negative tuples double the number of tuples through the query pipeline, thus reducing the pipeline bandwidth. In this paper, we put the negative tuples under a magnifying glass where we show its detailed realization in terms of its generation and its processing in various operators. Then, we present several optimization techniques that aim to reduce the overhead of the negative tuples approach. These optimizations can be applied independently or together to enhance the performance of negative tuples. A detailed experimental study, based on a prototype system implementation, shows the performance gains over the input-triggered approach of the negative tuples approach when accompanied with the proposed optimizations.