Github user aljoscha commented on a diff in the pull request:
https://github.com/apache/flink/pull/4943#discussion_r148924545
--- 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) {
+ this.type = type;
+ this.serializer = new AvroSerializer<>(type);
+ }
+
+ /**
+ * Private copy constructor.
+ */
+ private BackwardsCompatibleAvroSerializer(Class<T> type,
TypeSerializer<T> serializer) {
+ this.type = type;
+ this.serializer = serializer;
+ }
+
+ //
------------------------------------------------------------------------
+ // Properties
+ //
------------------------------------------------------------------------
+
+ @Override
+ public boolean isImmutableType() {
+ return serializer.isImmutableType();
+ }
+
+ @Override
+ public int getLength() {
+ return serializer.getLength();
+ }
+
+ //
------------------------------------------------------------------------
+ // Serialization
+ //
------------------------------------------------------------------------
+
+ @Override
+ public T createInstance() {
+ return serializer.createInstance();
+ }
+
+ @Override
+ public void serialize(T value, DataOutputView target) throws
IOException {
+ serializer.serialize(value, target);
+ }
+
+ @Override
+ public T deserialize(DataInputView source) throws IOException {
+ return serializer.deserialize(source);
+ }
+
+ @Override
+ public T deserialize(T reuse, DataInputView source) throws IOException {
+ return serializer.deserialize(reuse, source);
+ }
+
+ //
------------------------------------------------------------------------
+ // Copying
+ //
------------------------------------------------------------------------
+
+ @Override
+ public T copy(T from) {
+ return serializer.copy(from);
+ }
+
+ @Override
+ public T copy(T from, T reuse) {
+ return serializer.copy(from, reuse);
+ }
+
+ @Override
+ public void copy(DataInputView source, DataOutputView target) throws
IOException {
+ serializer.copy(source, target);
+ }
+
+ //
------------------------------------------------------------------------
+ // Utilities
+ //
------------------------------------------------------------------------
+
+ @Override
+ public TypeSerializer<T> duplicate() {
+ return new BackwardsCompatibleAvroSerializer<>(type,
serializer.duplicate());
+ }
+
+ @Override
+ public int hashCode() {
+ return type.hashCode();
+ }
+
+ @Override
+ public boolean equals(Object obj) {
+ if (obj == this) {
+ return true;
+ }
+ else if (obj != null && obj.getClass() ==
BackwardsCompatibleAvroSerializer.class) {
+ final BackwardsCompatibleAvroSerializer that =
(BackwardsCompatibleAvroSerializer) obj;
+ return this.type == that.type &&
this.serializer.equals(that.serializer);
+ }
+ else {
+ return false;
+ }
+ }
+
+ @Override
+ public boolean canEqual(Object obj) {
+ return obj.getClass() == this.getClass();
+ }
+
+ @Override
+ public String toString() {
+ return getClass().getName() + " (" + type.getName() + ')';
+ }
+
+ //
------------------------------------------------------------------------
+ // Configuration Snapshots and Upgrades
+ //
------------------------------------------------------------------------
+
+ @Override
+ public TypeSerializerConfigSnapshot snapshotConfiguration() {
+ // we return the configuration of the actually used serializer
here
+ return serializer.snapshotConfiguration();
+ }
+
+ @Override
+ @SuppressWarnings("deprecation")
+ public CompatibilityResult<T>
ensureCompatibility(TypeSerializerConfigSnapshot configSnapshot) {
+ if (configSnapshot instanceof
AvroSchemaSerializerConfigSnapshot ||
+ configSnapshot instanceof
AvroSerializerConfigSnapshot) {
+
+ // avro serializer, nice :-)
+ checkState(serializer instanceof AvroSerializer,
+ "Serializer was changed backwards to
PojoSerializer and now encounters AvroSerializer snapshot.");
+
+ return serializer.ensureCompatibility(configSnapshot);
+ }
+ else if (configSnapshot instanceof
PojoSerializerConfigSnapshot) {
+ // common previous case
+
checkState(SpecificRecordBase.class.isAssignableFrom(type),
+ "BackwardsCompatibleAvroSerializer
resuming a state serialized " +
+ "via a PojoSerializer,
but not for an Avro Specific Record");
+
+ final AvroTypeInfo<? extends SpecificRecordBase>
typeInfo =
+ new
AvroTypeInfo<>(type.asSubclass(SpecificRecordBase.class));
+
+ @SuppressWarnings("unchecked")
+ final TypeSerializer<T> pojoSerializer =
+ (TypeSerializer<T>)
typeInfo.createPojoSerializer(new ExecutionConfig());
--- End diff --
I think this will not work for any nested serialisers that actually need a
proper execution config. For example, any nested Kryo serialisers might have
had custom type registrations that they now can't pick up from the
`ExecutionConfig`.
Ah, it might work because they're picked up from the snapshot?
---
