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https://issues.apache.org/jira/browse/FLINK-4856?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15877933#comment-15877933
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ASF GitHub Bot commented on FLINK-4856:
---------------------------------------
Github user aljoscha commented on a diff in the pull request:
https://github.com/apache/flink/pull/3336#discussion_r102426841
--- Diff: docs/dev/stream/state.md ---
@@ -118,6 +118,11 @@ added to the state. Contrary to `ReducingState`, the
aggregate type may be diffe
of elements that are added to the state. The interface is the same as for
`ListState` but elements
added using `add(T)` are folded into an aggregate using a specified
`FoldFunction`.
+* `MapState<UK, UV>`: This keeps a list of mappings. You can put key-value
pairs into the state and retrieve
+retrieve an `Iterable` over all currently stored mappings. Mappings are
added using `put(UK, UV)` or
--- End diff --
duplicate "retrieve"
> Add MapState for keyed streams
> ------------------------------
>
> Key: FLINK-4856
> URL: https://issues.apache.org/jira/browse/FLINK-4856
> Project: Flink
> Issue Type: New Feature
> Components: DataStream API, State Backends, Checkpointing
> Reporter: Xiaogang Shi
> Assignee: Xiaogang Shi
>
> Many states in keyed streams are organized as key-value pairs. Currently,
> these states are implemented by storing the entire map into a ValueState or a
> ListState. The implementation however is very costly because all entries have
> to be serialized/deserialized when updating a single entry. To improve the
> efficiency of these states, MapStates are urgently needed.
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