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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-4856) Add MapState for keyed streams
Date Wed, 22 Feb 2017 10:24:44 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4856?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15877932#comment-15877932

ASF GitHub Bot commented on FLINK-4856:

Github user aljoscha commented on a diff in the pull request:

    --- 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 
    +`putAll(map<UK, UV>)`. The value associated with a user key can be retrieved using
`get(UK)`. The iterable
    --- End diff --
    lowercase `map`

> 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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