(RS)T -> (RT)S
(RS)T -> (TS)R
If JoinCommuteRule is enabled, only enabling JoinPushThroughJoinRule.right can achieve the same alternative with JoinPushThroughJoinRule.left, vice versa (suppose they are connected). So there is no need to enable left and right instances at the same time, which will slow down the optimization dramatically, e.g TPCH q05, q07 in TpchTest.java never finish. There is also the same bug report from .
Meanwhile, JoinPushThroughJoinRule matches RelNode.class, which is unnecessary. It should be just a group, or RelSet / RelSubset, as a place holder, because we don't care about what exactly the top join's right child is. But since the rule is designed to work with both HepPlanner and VolcanoPlanner, so just bear with the slowness.