[GitHub] [flink] tzulitai commented on a change in pull request #8565: [FLINK-11947] Support MapState value schema evolution for RocksDB

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tzulitai commented on a change in pull request #8565: [FLINK-11947] Support MapState value schema evolution for RocksDB
URL: https://github.com/apache/flink/pull/8565#discussion_r289757845
 
 

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 File path: flink-state-backends/flink-statebackend-rocksdb/src/main/java/org/apache/flink/contrib/streaming/state/RocksDBKeyedStateBackend.java
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 @@ -538,13 +539,19 @@ public void notifyCheckpointComplete(long completedCheckpointId) throws Exceptio
 	 * the key here, which is made up of key group, key, namespace and map key
 	 * (in case of MapState).
 	 */
+	@SuppressWarnings("unchecked")
 	private <N, S extends State, SV> void migrateStateValues(
 		StateDescriptor<S, SV> stateDesc,
 		Tuple2<ColumnFamilyHandle, RegisteredKeyValueStateBackendMetaInfo<N, SV>> stateMetaInfo) throws Exception {
 
 		if (stateDesc.getType() == StateDescriptor.Type.MAP) {
-			throw new StateMigrationException("The new serializer for a MapState requires state migration in order for the job to proceed." +
-				" However, migration for MapState currently isn't supported.");
+			TypeSerializer priorUserKeySerializer = ((MapSerializer) stateMetaInfo.f1.getPreviousStateSerializer()).getKeySerializer();
+			TypeSerializer newUserKeySerializer = ((MapSerializer) stateMetaInfo.f1.getStateSerializer()).getKeySerializer();
+			TypeSerializerSchemaCompatibility compatibility = priorUserKeySerializer.snapshotConfiguration().resolveSchemaCompatibility(newUserKeySerializer);
 
 Review comment:
   This seems to be incorrect.
   You should be able to get the snapshot of the prior user key serializer in the restored meta info snapshots map.
   You do not need extra work in creating a new serializer snapshot just for the purpose of performing a compatibility check.

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