[GitHub] [hudi] yuzhaojing commented on a change in pull request #3915: [HUDI-2677] Add DFS based message queue for flink writer

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yuzhaojing commented on a change in pull request #3915:
URL: https://github.com/apache/hudi/pull/3915#discussion_r742669034



##########
File path: hudi-flink/src/main/java/org/apache/hudi/sink/message/MessageBus.java
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@@ -0,0 +1,173 @@
+/*
+ * 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.hudi.sink.message;
+
+import org.apache.hudi.common.fs.FSUtils;
+import org.apache.hudi.common.table.HoodieTableMetaClient;
+import org.apache.hudi.common.util.FileIOUtils;
+import org.apache.hudi.common.util.ValidationUtils;
+import org.apache.hudi.util.StreamerUtil;
+
+import org.apache.hadoop.fs.FSDataInputStream;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+
+/**
+ * A message bus for transferring the checkpoint messages.
+ *
+ * <p>Each time the driver starts a new instant, it writes a commit message into the bus, the write tasks
+ * then consume the message and unblocking the data flush.
+ *
+ * <p>Why we use the DFS based message queue instead of sending
+ * the {@link org.apache.flink.runtime.operators.coordination.OperatorEvent} ?
+ * The write task handles the operator event using the main mailbox executor which has the lowest priority for mails,
+ * it is also used to process the inputs. When the write task blocks and waits for the operator event to ack the valid instant to write,
+ * it actually blocks all the following events in the mailbox, the operator event can never be consumed then it causes deadlock.
+ *
+ * <p>The message bus is also more lightweight than the active timeline.
+ */
+public abstract class MessageBus implements AutoCloseable {
+
+  public static final long INITIAL_CKP_ID = 0L;
+
+  public static final String ABORTED_CKP_INSTANT = "aborted";
+
+  protected static final int MESSAGE_QUEUE_LENGTH = 20;
+
+  protected static final int CLIENT_MESSAGE_CACHE_SIZE = 10;

Review comment:
       Should we add these Config in FlinkOptions?




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