Joining Punctuated Streams

We focus on stream join optimization by exploiting the constraints that are dynamically embedded into data streams to signal the end of transmitting certain attribute values. These constraints are called punctuations. Our stream join operator, PJoin, is able to remove no-longer-useful data from the state in a timely manner based on punctuations, thus reducing memory overhead and improving the efficiency of probing. We equip PJoin with several alternate strategies for purging the state and for propagating punctuations to benefit down-stream operators. We also present an extensive experimental study to explore the performance gains achieved by purging state as well as the trade-off between different purge strategies. Our experimental results of comparing the performance of PJoin with XJoin, a stream join operator without a constraint-exploiting mechanism, show that PJoin significantly outperforms XJoin with regard to both memory overhead and throughput.