Abstract
Adaptive query processing scheme attempts to reoptimize query plans during the course of query execution. This chapter proposes a variety of techniques for adaptive query processing, varying in the granularity at which they can make decisions. The eddy is the most aggressive of these techniques, with the flexibility to choose tuple-by-tuple how to order the application of operators. The chapter addresses a fundamental limitation of the original eddies proposal—the burden of history in routing. The routing decisions have long-term effects on the state of operators in the query, and can severely constrain the ability of the eddy to adapt over time. Further, the chapter proposes a mechanism, STAIRs, that allows the query engine to manipulate the state stored inside the operators and undo the effects of past routing decisions. It analyzes that eddies with STAIRs achieve both high adaptivity and good performance in the face of uncertainty, outperforming prior eddy proposals by orders of magnitude.
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