hsyuan opened a new pull request #1958:
URL: https://github.com/apache/calcite/pull/1958


   JIRA: CALCITE-3968
   
   JoinPushThroughJoinRule.right does
   (RS)T -> (RT)S
   
   JoinPushThroughJoinRule.left does
   (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 [1].
   
   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.
   
   [1] 
https://lists.apache.org/thread.html/r195c267ef15f50aa21bbcefd7bf523f8bf2495b2345fd163e91e3c36%40%3Cdev.calcite.apache.org%3E


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