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

["Stefan Richter (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-6353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15979042#comment-15979042 ] 

Stefan Richter commented on FLINK-6353:
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Just a small idea: do you think that from a users perspective we should simply allow to implement both, {{Checkpointed}} and the new {{CheckpointedFunction}} with the result that {{CheckpointedFunction}} overrides {{Checkpointed}} for snapshots, essentially making it equivalent to {{CheckpointedRestoring}}. We can log that that {{Checkpointed}} is disabled on the snapshots. Then, starting from the next savepoint, the {{Checkpointed}} interface could be dropped at any time, or kept for backwards compatibility. This way we could avoid fiddling around with to many different interfaces.

> 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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