codenohup commented on code in PR #25961:
URL: https://github.com/apache/flink/pull/25961#discussion_r1916191046


##########
flink-datastream/src/main/java/org/apache/flink/datastream/impl/extension/join/operators/TwoInputJoinProcessFunction.java:
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@@ -0,0 +1,59 @@
+/*
+ * 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.flink.datastream.impl.extension.join.operators;
+
+import org.apache.flink.datastream.api.common.Collector;
+import org.apache.flink.datastream.api.context.PartitionedContext;
+import org.apache.flink.datastream.api.extension.join.JoinFunction;
+import org.apache.flink.datastream.api.extension.join.JoinType;
+import 
org.apache.flink.datastream.api.function.TwoInputNonBroadcastStreamProcessFunction;
+
+/**
+ * Wrap the user-defined {@link JoinFunction} as {@link 
TwoInputNonBroadcastStreamProcessFunction}
+ * to execute the Join operation within Join extension.
+ */
+public class TwoInputJoinProcessFunction<IN1, IN2, OUT>
+        implements TwoInputNonBroadcastStreamProcessFunction<IN1, IN2, OUT> {

Review Comment:
   Hi, @reswqa 
   
   Currently, broadcast join is not supported because the data on the broadcast 
side cannot be stored using keyed state; it can only be stored using broadcast 
state. But currently the broadcast state only supports map types, and the value 
in the map needs to be set to a list type. This results in potential 
serialization overhead every time data is written, as the list needs to be 
serialized. 
   We think the implementation has poor performance, which is why it is not yet 
supported. In the future, we will look for ways to support broadcast join.



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