[GitHub] [pulsar] sijie commented on a change in pull request #4911: expose getLastMessageId method in ConsumerImpl

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sijie commented on a change in pull request #4911: expose getLastMessageId method in ConsumerImpl
URL: https://github.com/apache/pulsar/pull/4911#discussion_r312687864
 
 

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 File path: pulsar-client/src/main/java/org/apache/pulsar/client/impl/MultiMessageIdImpl.java
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 @@ -0,0 +1,54 @@
+/**
+ * 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.pulsar.client.impl;
+
+import java.util.Map;
+import java.util.Objects;
+import lombok.Getter;
+import org.apache.pulsar.client.api.MessageId;
+import sun.reflect.generics.reflectiveObjects.NotImplementedException;
+
+/**
+ * A MessageId implementation that contains a map of <partitionName, MessageId>.
+ * This is useful when MessageId is need for partition/multi-topics/pattern consumer.
+ * e.g. seek(), ackCumulative(), getLastMessageId().
+ */
+public class MultiMessageIdImpl implements MessageId {
+    @Getter
+    private Map<String, MessageId> map;
+
+    MultiMessageIdImpl(Map<String, MessageId> map) {
+        this.map = map;
+    }
+
+    @Override
+    public byte[] toByteArray() {
+        throw new NotImplementedException();
 
 Review comment:
   I think we should consider implementing this. In streaming applications, they tends to store `messageId` along with the state. so that the streaming applications can restore the state back. we need to provide a consistent behavior for how to serialize and deserialize different message id implementations.
   
   Can you add a task for it and link it here? Also consider making a PIP for discussing uniforming the serialization and deserialization of message id implementations (basically we need the ability to deserialize the message ids from the byte array in a consistent way).

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