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https://issues.apache.org/jira/browse/FLINK-5929?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15941791#comment-15941791
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ASF GitHub Bot commented on FLINK-5929:
---------------------------------------
Github user sjwiesman commented on the issue:
https://github.com/apache/flink/pull/3479
Done! Thank you for for helping me get this feature merged in. This has to
be one of the most painless commits I've ever made to an open source project of
this size.
> 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
> Assignee: Seth Wiesman
> Fix For: 1.3.0
>
>
> 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 horizon.
> - 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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