zhengruifeng commented on code in PR #36438:
URL: https://github.com/apache/spark/pull/36438#discussion_r872295375


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sql/core/src/main/scala/org/apache/spark/sql/execution/adaptive/PropagateEmptyPartitions.scala:
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@@ -0,0 +1,199 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+
+package org.apache.spark.sql.execution.adaptive
+
+import scala.collection.mutable
+
+import org.apache.spark.sql.catalyst.plans._
+import org.apache.spark.sql.execution._
+import org.apache.spark.sql.execution.exchange._
+import org.apache.spark.sql.execution.joins._
+
+/**
+ * A rule to propagate empty partitions, so that some unnecessary shuffle read 
can be skipped.

Review Comment:
   IIUC, SMJ can skip reading the uncessary (but already fetched) side, but it 
can not skip fetching the uncessary partitions.
   
   Sorry for the late reply, just back from vacation.



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