[GitHub] [spark] maryannxue commented on a change in pull request #27493: [SPARK-30751][SQL] Combine the skewed readers into one in AQE skew join optimizations

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maryannxue commented on a change in pull request #27493: [SPARK-30751][SQL] Combine the skewed readers into one in AQE skew join optimizations
URL: https://github.com/apache/spark/pull/27493#discussion_r377136054
 
 

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 File path: sql/core/src/main/scala/org/apache/spark/sql/execution/adaptive/OptimizeSkewedJoin.scala
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 @@ -156,60 +155,133 @@ case class OptimizeSkewedJoin(conf: SQLConf) extends Rule[SparkPlan] {
           |${getSizeInfo(rightMedSize, rightStats.bytesByPartitionId.max)}
         """.stripMargin)
 
-      val skewedPartitions = mutable.HashSet[Int]()
-      val subJoins = mutable.ArrayBuffer[SparkPlan]()
-      for (partitionId <- 0 until numPartitions) {
-        val isLeftSkew = isSkewed(leftStats, partitionId, leftMedSize)
-        val isRightSkew = isSkewed(rightStats, partitionId, rightMedSize)
-        val leftMapIdStartIndices = if (isLeftSkew && supportSplitOnLeftPartition(joinType)) {
-          getMapStartIndices(left, partitionId)
-        } else {
-          Array(0)
-        }
-        val rightMapIdStartIndices = if (isRightSkew && supportSplitOnRightPartition(joinType)) {
-          getMapStartIndices(right, partitionId)
-        } else {
-          Array(0)
-        }
+      val leftSidePartitions = mutable.ArrayBuffer.empty[ShufflePartitionSpec]
+      val rightSidePartitions = mutable.ArrayBuffer.empty[ShufflePartitionSpec]
+      val nonSkewPartitionIndices = mutable.ArrayBuffer.empty[Int]
 
 Review comment:
   Can we add a comment here about `nonSkewPartitionIndices` used to delay creation of non-skew partitions and for potential coalescing?

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