leanken commented on a change in pull request #29455:
URL: https://github.com/apache/spark/pull/29455#discussion_r472592607



##########
File path: 
sql/core/src/main/scala/org/apache/spark/sql/execution/adaptive/EliminateNullAwareAntiJoin.scala
##########
@@ -20,22 +20,50 @@ package org.apache.spark.sql.execution.adaptive
 import 
org.apache.spark.sql.catalyst.planning.ExtractSingleColumnNullAwareAntiJoin
 import org.apache.spark.sql.catalyst.plans.logical.{LocalRelation, LogicalPlan}
 import org.apache.spark.sql.catalyst.rules.Rule
+import org.apache.spark.sql.execution.exchange.ShuffleExchangeExec
 import org.apache.spark.sql.execution.joins.EmptyHashedRelationWithAllNullKeys
+import 
org.apache.spark.sql.execution.metric.SQLShuffleWriteMetricsReporter.SHUFFLE_RECORDS_WRITTEN
 
 /**
- * This optimization rule detects and convert a NAAJ to an Empty LocalRelation
- * when buildSide is EmptyHashedRelationWithAllNullKeys.
+ * This optimization rule try to Eliminate NAAJ by following patterns.
+ * 1. Convert a NAAJ to an Empty LocalRelation when buildSide is 
EmptyHashedRelationWithAllNullKeys.
+ * 2. Convert a NAAJ to left plan when buildSide is empty.
  */
 object EliminateNullAwareAntiJoin extends Rule[LogicalPlan] {
 
-  private def canEliminate(plan: LogicalPlan): Boolean = plan match {
+  private def canConvertToEmptyLocalRelation(plan: LogicalPlan): Boolean = 
plan match {
     case LogicalQueryStage(_, stage: BroadcastQueryStageExec) if 
stage.resultOption.get().isDefined
       && stage.broadcast.relationFuture.get().value == 
EmptyHashedRelationWithAllNullKeys => true
+    case LogicalQueryStage(_, stage: ShuffleQueryStageExec) if 
stage.resultOption.get().isDefined =>
+      // Equivalent to EmptyHashedRelationWithAllNullKeys
+      val nullPartitionKeyMetrics = 
stage.shuffle.asInstanceOf[ShuffleExchangeExec]
+        .metrics.get(ShuffleExchangeExec.NULL_PARTITION_KEY_RECORDS_WRITTEN)
+      if (nullPartitionKeyMetrics.isDefined && 
nullPartitionKeyMetrics.get.value > 0L) {
+        true
+      } else {
+        false
+      }
+    case _ => false
+  }
+
+  private def canConvertToLeftPlan(plan: LogicalPlan): Boolean = plan match {

Review comment:
       both canConvertXXX is to remove AntiJoin. maybe canRemoveAntiJoin is not 
the best option.




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