[GitHub] [kafka] cmccabe commented on a change in pull request #9998: KAFKA-12250; Add metadata record serde for KIP-631

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cmccabe commented on a change in pull request #9998:
URL: https://github.com/apache/kafka/pull/9998#discussion_r569633608



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File path: metadata/src/main/java/org/apache/kafka/metadata/MetadataRecordSerde.java
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@@ -0,0 +1,62 @@
+/*
+ * 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.kafka.metadata;
+
+import org.apache.kafka.common.metadata.MetadataRecordType;
+import org.apache.kafka.common.protocol.ApiMessage;
+import org.apache.kafka.common.protocol.ObjectSerializationCache;
+import org.apache.kafka.common.protocol.Readable;
+import org.apache.kafka.common.protocol.Writable;
+import org.apache.kafka.common.utils.ByteUtils;
+import org.apache.kafka.raft.RecordSerde;
+
+public class MetadataRecordSerde implements RecordSerde<ApiMessageAndVersion> {
+
+    @Override
+    public ObjectSerializationCache newWriteContext() {
+        return new ObjectSerializationCache();
+    }
+
+    @Override
+    public int recordSize(ApiMessageAndVersion data, Object context) {
+        ObjectSerializationCache serializationCache = (ObjectSerializationCache) context;
+        int size = 0;
+        size += ByteUtils.sizeOfUnsignedVarint(data.message().apiKey());
+        size += ByteUtils.sizeOfUnsignedVarint(data.version());
+        size += data.message().size(serializationCache, data.version());
+        return size;
+    }
+
+    @Override
+    public void write(ApiMessageAndVersion data, Object context, Writable out) {
+        ObjectSerializationCache serializationCache = (ObjectSerializationCache) context;
+        out.writeUnsignedVarint(data.message().apiKey());
+        out.writeUnsignedVarint(data.version());
+        data.message().write(out, serializationCache, data.version());
+    }
+
+    @Override
+    public ApiMessageAndVersion read(Readable input, int size) {
+        short apiKey = (short) input.readUnsignedVarint();
+        short version = (short) input.readUnsignedVarint();

Review comment:
       It is a big savings overall, right?  2 bytes per record, for every record.  We use varints in the record format for the same reasons.
   
   Actually the question that @hachikuji raised earlier was whether we should have a third varint which comes first for message frame version, which is not unreasonable.




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