Github user tzulitai commented on a diff in the pull request:
https://github.com/apache/flink/pull/3834#discussion_r115141585
--- Diff:
flink-core/src/main/java/org/apache/flink/api/common/typeutils/TypeSerializer.java
---
@@ -161,7 +162,93 @@
public abstract int hashCode();
- public boolean canRestoreFrom(TypeSerializer<?> other) {
- return equals(other);
+ //
--------------------------------------------------------------------------------------------
+ // Serializer configuration snapshotting & reconfiguring
+ //
--------------------------------------------------------------------------------------------
+
+ /**
+ * Create a snapshot of the serializer's current configuration to be
stored along with the managed state it is
+ * registered to (if any - this method is only relevant if this
serializer is registered for serialization of
+ * managed state).
+ *
+ * <p>The configuration snapshot should contain information about the
serializer's parameter settings and its
+ * serialization format. When a new serializer is registered to
serialize the same managed state that this
+ * serializer was registered to, the returned configuration snapshot
can be used to check with the new serializer
+ * if any data migration needs to take place.
+ *
+ * <p>Implementations can also return the singleton {@link
ForwardCompatibleSerializationFormatConfig#INSTANCE}
+ * configuration if they guarantee forwards compatibility. For example,
implementations that use serialization
+ * frameworks with built-in serialization compatibility, such as <a
href=https://thrift.apache.org/>Thrift</a> or
+ * <a
href=https://developers.google.com/protocol-buffers/>Protobuf</a>, is suitable
for this usage pattern. By
+ * returning the {@link
ForwardCompatibleSerializationFormatConfig#INSTANCE}, this informs Flink that
when managed
+ * state serialized using this serializer is restored, there is no need
to check for migration with the new
+ * serializer for the same state. In other words, new serializers are
always assumed to be fully compatible for the
+ * serialized state.
+ *
+ * @see TypeSerializerConfigSnapshot
+ * @see ForwardCompatibleSerializationFormatConfig
+ *
+ * @return snapshot of the serializer's current configuration.
+ */
+ public abstract TypeSerializerConfigSnapshot snapshotConfiguration();
+
+ /**
+ * Get the migration strategy to use this serializer based on the
configuration snapshot of a preceding
+ * serializer that was registered for serialization of the same managed
state (if any - this method is only
+ * relevant if this serializer is registered for serialization of
managed state).
+ *
+ * <p>Implementations need to return the resolved migration strategy.
The strategy can be one of the following:
+ * <ul>
+ * <li>{@link MigrationStrategy#noMigration()}: this signals Flink
that this serializer is compatible, or
+ * has been reconfigured to be compatible, to continue reading old
data, and that the
+ * serialization schema remains the same. No migration needs to be
performed.</li>
+ *
+ * <li>{@link
MigrationStrategy#migrateWithFallbackDeserializer(TypeSerializer)}: this
signals Flink that
+ * migration needs to be performed, because this serializer is not
compatible, or cannot be reconfigured to be
+ * compatible, for old data. Furthermore, in the case that the
preceding serializer cannot be found or
+ * restored to read the old data, the provided fallback
deserializer can be used.</li>
+ *
+ * <li>{@link MigrationStrategy#migrate()}: this signals Flink that
migration needs to be performed, because
+ * this serializer is not compatible, or cannot be reconfigured to
be compatible, for old data.</li>
+ * </ul>
+ *
+ * <p>This method is guaranteed to only be invoked if the preceding
serializer's configuration snapshot is not the
+ * singleton {@link
ForwardCompatibleSerializationFormatConfig#INSTANCE} configuration. In such
cases, Flink always
+ * assume that the migration strategy is {@link
MigrationStrategy#migrate()}.
+ *
+ * @see MigrationStrategy
+ *
+ * @param configSnapshot configuration snapshot of a preceding
serializer for the same managed state
+ *
+ * @return the result of the reconfiguration.
+ */
+ protected abstract MigrationStrategy<T>
getMigrationStrategy(TypeSerializerConfigSnapshot configSnapshot);
--- End diff --
Agreed. Refined the naming of this with 81dd0eb
---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at infrastruct...@apache.org or file a JIRA ticket
with INFRA.
---
