[jira] [Created] (FLINK-5932) Order of legacy vs new state initialization in the AbstractStreamOperator.

[Shang Yuanchun (Jira)]

Kostas Kloudas created FLINK-5932:
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             Summary: Order of legacy vs new state initialization in the AbstractStreamOperator.
                 Key: FLINK-5932
                 URL: https://issues.apache.org/jira/browse/FLINK-5932
             Project: Flink
          Issue Type: Bug
          Components: DataStream API
    Affects Versions: 1.2.0
            Reporter: Kostas Kloudas
             Fix For: 1.3.0


Currently in the `AbstractStreamOperator::initializeState(OperatorStateHandles stateHandles)`, the `restoreStreamCheckpointed` which is responsible for restoring state from previous Flink versions, (backwards compatibility) is called before the `initializeState(StateInitializationContext context)` which is responsible for initializing the state in Flink 1.2.

This has the negative side effect that when implementing the backwards compatibility strategy for a given operator, we have to restore the old state, store it in local variables, and register it with the new state abstractions in the `initializeState()` or the `open()`. This creates a lot of unnecessary code in the operators, and potential memory leaks if the local variables are not "null-ified".

This issue proposes to call the `restoreStreamCheckpointed` after the `initializeState(StateInitializationContext context)`. This way, the new operator state will have been initialized (e.g. keyed state), and the `restoreStreamCheckpointed` will be able to register its state directly with the new abstractions, instead of putting it in local variables and wait for the `initializeState` or the `open()` to re-register it.



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