Wander Join: Online Aggregation for Joins

Joins are expensive, and online aggregation over joins was proposed to mitigate the cost, which offers a nice and flexible tradeoff between query efficiency and accuracy in a continuous, online fashion. However, the state-of-the-art approach, in both internal and external memory, is based on ripple join, which is still very expensive and may also need very restrictive assumptions (e.g., tuples in a table are stored in random order). We introduce a new approach, wander join, to the online aggregation problem by performing random walks over the underlying join graph. We have also implemented and tested wander join in the latest PostgreSQL.