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https://issues.apache.org/jira/browse/FLINK-2922?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15147471#comment-15147471
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Gyula Fora commented on FLINK-2922:
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I think it would be also nice to extend the same general idea to all stateful
operators, so that users would have a straightforward way to query them without
having to hack that into the user functions.
An idea would be that for each state (statedescriptor) the user would also
define a query function that tells the system what should be the query output.
So if your state is a giant list you might only one to query the last element
anyways.
> Add Queryable Window Operator
> -----------------------------
>
> Key: FLINK-2922
> URL: https://issues.apache.org/jira/browse/FLINK-2922
> Project: Flink
> Issue Type: Improvement
> Components: Streaming
> Reporter: Aljoscha Krettek
> Assignee: Aljoscha Krettek
> Labels: requires-design-doc
> Attachments: FLINK-2922.pdf
>
>
> The idea is to provide a window operator that allows to query the current
> window result at any time without discarding the current result.
> For example, a user might have an aggregation window operation with tumbling
> windows of 1 hour. Now, at any time they might be interested in the current
> aggregated value for the currently in-flight hour window.
> The idea is to make the operator a two input operator where normal elements
> arrive on input one while queries arrive on input two. The query stream must
> be keyed by the same key as the input stream. If an input arrives for a key
> the current value for that key is emitted along with the query element so
> that the user can map the result to the query.
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