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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-5929) Allow Access to Per-Window State in ProcessWindowFunction
Date Sat, 25 Mar 2017 16:04:42 GMT

    [ https://issues.apache.org/jira/browse/FLINK-5929?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15941771#comment-15941771

ASF GitHub Bot commented on FLINK-5929:

Github user aljoscha commented on the issue:

    Thanks for implementing this! 😃 
    I just merged, could you please close this PR?

> Allow Access to Per-Window State in ProcessWindowFunction
> ---------------------------------------------------------
>                 Key: FLINK-5929
>                 URL: https://issues.apache.org/jira/browse/FLINK-5929
>             Project: Flink
>          Issue Type: Improvement
>          Components: DataStream API
>            Reporter: Aljoscha Krettek
> Right now, the state that a {{WindowFunction}} or {{ProcessWindowFunction}} can access
is scoped to the key of the window but not the window itself. That is, state is global across
all windows for a given key.
> For some use cases it is beneficial to keep state scoped to a window. For example, if
you expect to have several {{Trigger}} firings (due to early and late firings) a user can
keep state per window to keep some information between those firings.
> The per-window state has to be cleaned up in some way. For this I see two options:
>  - Keep track of all state that a user uses and clean up when we reach the window GC
>  - Add a method {{cleanup()}} to {{ProcessWindowFunction}} which is called when we reach
the window GC horizon that users can/should use to clean up their state.
> On the API side, we can add a method {{windowState()}} on {{ProcessWindowFunction.Context}}
that retrieves the per-window state and {{globalState()}} that would allow access to the (already
available) global state. The {{Context}} would then look like this:
> {code}
> /**
>  * The context holding window metadata
>  */
> public abstract class Context {
>     /**
>      * @return The window that is being evaluated.
>      */
>     public abstract W window();
>     /**
>      * State accessor for per-key and per-window state.
>      */
>     KeyedStateStore windowState();
>     /**
>      * State accessor for per-key global state.
>      */
>     KeyedStateStore globalState();
> }
> {code}

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