Load-balancing distributed outer joins through operator decomposition

High-performance data analytics largely relies on being able to efficiently execute various distributed data operators such as distributed joins. So far, large amounts of join methods have been proposed and evaluated in parallel and distributed environments. However, most of them focus on inner joins, and there is little published work providing the detailed implementations and analysis of outer joins. In this work, we present POPI (Partial Outer join & Partial Inner join), a novel method to load-balance large parallel outer joins by decomposing them into two operations: a large outer join over data that does not present significant skew in the input and an inner join over data presenting significant skew. We present the detailed implementation of our approach and show that POPI is implementable over a variety of architectures and underlying join implementations. Moreover, our experimental evaluation over a distributed memory platform also demonstrates that the proposed method is able to improve outer join performance under varying data skew and present excellent load-balancing properties, compared to current approaches.