Github user StephanEwen commented on the pull request:
https://github.com/apache/flink/pull/1527#issuecomment-181922703
@wangyangjun We actually merged all the changes concerning the state
abstraction.
To make this window join work seamlessly on Flink's state backends (memory,
or key/value stores, managed memory, ...) you would need to implement it
against the key/value state. That means that whenever you store data in the
operator, the data should go into the partitioned state that you can obtain
from the `AbstractStreamOperator` or the `RuntimeContext`.
I think that for this window operator, the `ListState` is a good choice,
where you can add values to a key and retrieve the list as a whole once the
windows are evaluated.
Please write back if you need some more pointers on the state abstraction.
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