LuciferYang commented on a change in pull request #29434:
URL: https://github.com/apache/spark/pull/29434#discussion_r472861979
##########
File path:
sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/StarJoinCostBasedReorderSuite.scala
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@@ -329,7 +329,7 @@ class StarJoinCostBasedReorderSuite extends PlanTest with
StatsEstimationTestBas
//
// Number of generated plans: 46 (vs. 82)
val query =
-
d1.join(t3).join(t4).join(f1).join(d2).join(t5).join(t6).join(d3).join(t1).join(t2)
+
d1.join(t3).join(t4).join(f1).join(d3).join(d2).join(t5).join(t6).join(t1).join(t2)
Review comment:
@cloud-fan Yep, in this case 2 candidates plan in level 4 has same
`Cost`, From the code, we can see which candidate is generated first and which
one we will choice.
Related codes as follow:
https://github.com/apache/spark/blob/3092527f7557b64ff9a5bedadfac8bb2f189a9b4/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CostBasedJoinReorder.scala#L209-L231
if `newJoinPlan` betterThan `existingPlan` will use `newJoinPlan` else use
`existingPlan` and Same cost candidate not trigger update.
In Scala 2.13 `HashMap` and `HashSet` has been rewritten, and I found the
iteration order of `oneSideCandidates` and `otherSideCandidates` from
`foundPlans` are changes through debug this case.
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