Github user aljoscha commented on a diff in the pull request:
https://github.com/apache/flink/pull/4943#discussion_r148924503
--- Diff:
flink-formats/flink-avro/src/main/java/org/apache/flink/formats/avro/typeutils/BackwardsCompatibleAvroSerializer.java
---
@@ -0,0 +1,215 @@
+/*
+ * 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.formats.avro.typeutils;
+
+import org.apache.flink.api.common.ExecutionConfig;
+import org.apache.flink.api.common.typeutils.CompatibilityResult;
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.api.common.typeutils.TypeSerializerConfigSnapshot;
+import
org.apache.flink.api.java.typeutils.runtime.KryoRegistrationSerializerConfigSnapshot;
+import
org.apache.flink.api.java.typeutils.runtime.PojoSerializer.PojoSerializerConfigSnapshot;
+import org.apache.flink.api.java.typeutils.runtime.kryo.KryoSerializer;
+import org.apache.flink.core.memory.DataInputView;
+import org.apache.flink.core.memory.DataOutputView;
+import
org.apache.flink.formats.avro.typeutils.AvroSerializer.AvroSchemaSerializerConfigSnapshot;
+import
org.apache.flink.formats.avro.typeutils.AvroSerializer.AvroSerializerConfigSnapshot;
+
+import org.apache.avro.specific.SpecificRecordBase;
+
+import java.io.IOException;
+
+import static org.apache.flink.util.Preconditions.checkState;
+
+/**
+ * An Avro serializer that can switch back to a KryoSerializer or a Pojo
Serializer, if
+ * it has to ensure compatibility with one of those.
+ *
+ * @param <T> The type to be serialized.
+ */
+public class BackwardsCompatibleAvroSerializer<T> extends
TypeSerializer<T> {
+
+ private static final long serialVersionUID = 1L;
+
+ /** The type to serialize. */
+ private final Class<T> type;
+
+ /** The type serializer currently used. Avro by default. */
+ private TypeSerializer<T> serializer;
+
+ /**
+ * Creates a new backwards-compatible Avro Serializer, for the given
type.
+ */
+ public BackwardsCompatibleAvroSerializer(Class<T> type) {
--- End diff --
nit: Call the other constructor?
---
