Github user StefanRRichter commented on a diff in the pull request:
https://github.com/apache/flink/pull/3834#discussion_r115139379
--- Diff:
flink-core/src/main/java/org/apache/flink/api/common/typeutils/MigrationStrategy.java
---
@@ -0,0 +1,87 @@
+/*
+ * 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.api.common.typeutils;
+
+import org.apache.flink.annotation.PublicEvolving;
+
+/**
+ * A {@code MigrationStrategy} contains information about how to perform
migration of data written
+ * by an older serializer so that new serializers can continue to work on
them.
+ *
+ * @param <T> the type of the data being migrated.
+ */
+@PublicEvolving
+public final class MigrationStrategy<T> {
+
+ /** Whether or not migration is required. */
+ private final boolean requiresStateMigration;
+
+ /**
+ * The fallback deserializer to use, in the case the preceding
serializer cannot be found.
+ *
+ * <p>This is only relevant if migration is required.
+ */
+ private final TypeSerializer<T> fallbackDeserializer;
+
+ /**
+ * Returns a strategy that simply signals that no migration needs to be
performed.
+ *
+ * @return a strategy that does not perform migration
+ */
+ public static <T> MigrationStrategy<T> noMigration() {
+ return new MigrationStrategy<>(false, null);
+ }
+
+ /**
+ * Returns a strategy that signals migration to be performed, and in
the case that the
+ * preceding serializer cannot be found, a provided fallback
deserializer can be
+ * used.
+ *
+ * @param fallbackDeserializer a fallback deserializer that can be used
to read old data for the migration
+ * in the case that the preceding
serializer cannot be found.
+ *
+ * @return a strategy that performs migration with a fallback
deserializer to read old data.
+ */
+ public static <T> MigrationStrategy<T>
migrateWithFallbackDeserializer(TypeSerializer<T> fallbackDeserializer) {
+ return new MigrationStrategy<>(true, fallbackDeserializer);
+ }
+
+ /**
+ * Returns a strategy that signals migration to be performed, without a
fallback deserializer.
+ * If the preceding serializer cannot be found, the migration fails
because the old data cannot be read.
+ *
+ * @return a strategy that performs migration, without a fallback
deserializer.
+ */
+ public static <T> MigrationStrategy<T> migrate() {
--- End diff --
Maybe this should be named `migrationRequired`?
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