Execution plans produced by traditional query optimizers for data integration queries may yield poor performance for several reasons. The cost estimates may be inaccurate, the memory available at run-time may be insufficient, or the data delivery rate can be unpredictable. All these problems have led database researchers and implementors to resort to dynamic strategies to correct or adapt the static QEP. In this paper, we identify the different basic techniques that must be integrated in a dynamic query engine. Following on our recent work [6] on the problem of unpredictable data arrival rates, we propose a dynamic query processing architecture which includes three dynamic layers: the dynamic query optimizer, the scheduler and the query evaluator. Having a three-layer dynamic architecture allows reducing significantly the overheads of the dynamic strategies.
Luc Bouganim, Françoise Fabret, C. Mohan, P