[GitHub] [spark] LantaoJin commented on a change in pull request #29021: [SPARK-32201][SQL] More general skew join pattern matching

[GitBox <gi...@apache.org>]

LantaoJin commented on a change in pull request #29021:
URL: https://github.com/apache/spark/pull/29021#discussion_r456311324



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File path: sql/core/src/main/scala/org/apache/spark/sql/execution/adaptive/OptimizeLocalShuffleReader.scala
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@@ -142,6 +142,14 @@ object OptimizeLocalShuffleReader {
   def canUseLocalShuffleReader(plan: SparkPlan): Boolean = plan match {
     case s: ShuffleQueryStageExec =>
       s.shuffle.canChangeNumPartitions
+    // This CustomShuffleReaderExec used in skew side, its numPartitions increased.

Review comment:
       Not exactly. In this more general skew join handling, we can match more patterns. For example, we can handle skew join like https://user-images.githubusercontent.com/1853780/87743215-01e9e780-c81b-11ea-97d9-f274b379912e.png. The number partitions of `CustomShuffleReader in the the BCJ (changed from SMJ by AE) is not equals to the anther side. So simply, I disable `createLocalReader`.




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