Join Reordering by Join Simulation

We introduce a framework for reordering join pipelines at runtime in a database system. This framework incorporates novel techniques for simulating the execution of a join pipeline using random samples and statistical summaries. Our simulation techniques provide accurate runtime cardinality estimates along all alternative execution paths of a join pipeline. These estimates are then utilized to compare costs of alternative execution paths in a dynamic fashion, and reorder the pipeline if a better alternative path is found. We describe simulation techniques for pipelines of different kinds of join operators. We present an experimental evaluation of a prototype implementation of our framework in an open source data manager. The results demonstrate the feasibility and utility of the approach presented herein.