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https://issues.apache.org/jira/browse/FLINK-5590?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15833260#comment-15833260
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Xiaogang Shi commented on FLINK-5590:
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[~StephanEwen], do you have any ideas of the solution?
I think {{KvState}} already provides some needed internal methods. Maybe we can
extend it to create the internal state hierarchy?
> Create a proper internal state hierarchy
> ----------------------------------------
>
> Key: FLINK-5590
> URL: https://issues.apache.org/jira/browse/FLINK-5590
> Project: Flink
> Issue Type: Improvement
> Components: State Backends, Checkpointing
> Affects Versions: 1.2.0
> Reporter: Stephan Ewen
> Assignee: Stephan Ewen
> Fix For: 1.3.0
>
>
> Currently, the state interfaces (like {{ListState}}, {{ValueState}},
> {{ReducingState}}) are very sparse and contain only methods exposed to the
> users. That makes sense to keep the public stable API minimal
> At the same time, the runtime needs more methods for its internal interaction
> with state, such as:
> - setting namespaces
> - accessing raw values
> - merging namespaces
> These are currently realized by re-creating or re-obtaining the state objects
> from the KeyedStateBackend. That method causes quite an overhead for each
> access to the state
> The KeyedStateBackend tries to do some tricks to reduce that overhead, but
> does it only partially and induces other overhead in the course.
> The root cause of all these issues is a problem in the design: There is no
> proper "internal state abstraction" in a similar way as there is an external
> state abstraction (the public state API).
> We should add a similar hierarchy of states for the internal methods. It
> would look like in the example below:
> {code}
> * State
> * |
> * +-------------------InternalKvState
> * | |
> * MergingState |
> * | |
> * +-----------------InternalMergingState
> * | |
> * +--------+------+ |
> * | | |
> * ReducingState ListState +-----+-----------------+
> * | | | |
> * +-----------+ +----------- -----------------InternalListState
> * | |
> * +---------InternalReducingState
> {code}
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