[jira] [Created] (FLINK-6353) Restoring using CheckpointedRestoring does not work from 1.2 to 1.2

["Aljoscha Krettek (JIRA)" <ji...@apache.org>]

Aljoscha Krettek created FLINK-6353:
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             Summary: Restoring using CheckpointedRestoring does not work from 1.2 to 1.2
                 Key: FLINK-6353
                 URL: https://issues.apache.org/jira/browse/FLINK-6353
             Project: Flink
          Issue Type: Bug
          Components: DataStream API, State Backends, Checkpointing
    Affects Versions: 1.2.0, 1.2.1
            Reporter: Aljoscha Krettek
            Assignee: Aljoscha Krettek


State that was checkpointed using {{Checkpointed}} (on a user function) cannot be restored using {{CheckpointedRestoring}} when the savepoint was done on Flink 1.2. The reason is an overzealous check in {{AbstractUdfStreamOperator}} that only restores from "legacy" operator state using {{CheckpointedRestoring}} when the stream is a {{Migration}} stream.

We can remove that check but still need to make sure to read away the byte that indicates whether there is legacy state, which is written when we're restoring from a Flink 1.1 savepoint.

Also, if we remove the check, the procedure for a user to migrate a user function away from the {{Checkpointed}} interface is this:
 # Perform savepoint with user function still implementing {{Checkpointed}}, shutdown job
 # Change user function to implement {{CheckpointedRestoring}}
 # Restore from previous savepoint, user function has to somehow move the state that is restored using {{CheckpointedRestoring}} to another type of state, .e.g operator state, using the {{OperatorStateStore}}.
 # Perform another savepoint, shutdown job
 # Remove {{CheckpointedRestoring}} interface from user function
 # Restore from the second savepoint
 # Done.

If the {{CheckpointedRestoring}} interface is not removed as prescribed in the last steps then a future restore of a new savepoint will fail because Flink will try to read legacy operator state that is not there anymore.

The above steps also apply to Flink 1.3, when a user want's to move away from the {{Checkpointed}} interface.



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