[GitHub] [spark] cloud-fan commented on a change in pull request #28226: [SPARK-31452][SQL] Do not create partition spec for 0-size partitions in AQE

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

cloud-fan commented on a change in pull request #28226:
URL: https://github.com/apache/spark/pull/28226#discussion_r411102045



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File path: sql/core/src/main/scala/org/apache/spark/sql/execution/adaptive/OptimizeSkewedJoin.scala
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@@ -88,9 +88,11 @@ case class OptimizeSkewedJoin(conf: SQLConf) extends Rule[SparkPlan] {
   private def targetSize(sizes: Seq[Long], medianSize: Long): Long = {
     val advisorySize = conf.getConf(SQLConf.ADVISORY_PARTITION_SIZE_IN_BYTES)
     val nonSkewSizes = sizes.filterNot(isSkewed(_, medianSize))
-    // It's impossible that all the partitions are skewed, as we use median size to define skew.
-    assert(nonSkewSizes.nonEmpty)
-    math.max(advisorySize, nonSkewSizes.sum / nonSkewSizes.length)
+    if (nonSkewSizes.isEmpty) {

Review comment:
       because we calculate the median size based on the original map stats, but the input partitions are coalesced. It's possible all partitions (after coalesce) are skewed.




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