Query Plan Optimization and Migration Strategy over Data Stream

Continuous queries are the more interesting class of data stream queries. The answer to a continuous query is continuously produced over time unless stopped artificially. During an executed continuous query, the run environment changes continuously, meanwhile some properties of data stream itself change too, such as input rate, selectivity of operators and execute time and so on. In order to adapt the continuity of queries and variability of system environment and date itself during continuous query, this paper presents a query plan optimization and migration strategy based on multi-factors and gives corresponding algorithm. Experiments have proved that this optimization and migration strategy ensures output results correctness and time sequence, meanwhile validly increases throughput and output rate and reduces output time latency.