Towards multi-way join aware optimizer in SAP HANA
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Abstract
Existing binary join based plans may be suboptimal for important, emerging applications. Typical query optimizers enumerate plans using binary joins only. In this paper, we introduce the multi-way join aware optimizer in SAP HANA. The naive way to extend the existing query optimizer to be aware of multi-way joins ( m -way joins for short) is to enumerate m -way joins on top of a traditional binary join enumeration framework. However, many different binary joins correspond to the same m -way join. Thus, unnecessary join enumerations would be required for such naive integration. To solve this problem, we introduce the new concept of an m -way join unit and explain how the construction of join units is plugged into the SAP HANA query optimizer. We also provide a series of optimizer enhancements by exploiting m -way join unit characteristics. Using TPC-H and our customer workloads, we showcase the superiority of our m -way join aware optimizer.
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