Incremental checkpoints are currently not externalizible. The missing piece is familiarizing the SavepointSerializer(s) with the new state handles classes that we added for incremental checkpointing. Currently, some of those (e.g. org.apache.flink.contrib.streaming.state.RocksDBIncrementalKeyedStateHandle) currently live in the contrib.rocksdb package and need to be migrated. We can also push them to a different abstraction level, i.e. IncrementalKeyedStateHandle with some private data, referenced existing shared data (from previous checkpoints), and (presumably) newly created shared data (first created by the current checkpoint).