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https://issues.apache.org/jira/browse/BEAM-1612?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15996375#comment-15996375
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Stephan Ewen commented on BEAM-1612:
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[~kenn] Ah, I think there are two notions floating around about what a bundle 
should be:

  - The bundle of records between persistence boundaries (flush, commit, 
checkpoint, whatever) - [~kenn]'s notion
  - Some arbitrary form of mini batching [~aljoscha]'s notion

I think that notifying the user code about persistence boundaries is actually a 
good idea, if they want to coordinate their flushes / rollover / etc at these 
boundaries. For the just arbitrary mini batching - what speaks against 
small/fast processing time windows for that?

> Support real Bundle in Flink runner
> -----------------------------------
>
>                 Key: BEAM-1612
>                 URL: https://issues.apache.org/jira/browse/BEAM-1612
>             Project: Beam
>          Issue Type: Improvement
>          Components: runner-flink
>            Reporter: Jingsong Lee
>
> The Bundle is very important in the beam model. Users can use the bundle to 
> flush buffer, can reuse many heavyweight resources in a bundle. Most IO 
> plugins use the bundle to flush. 
> Moreover, FlinkRunner can also use Bundle to reduce access to the FlinkState, 
> such as first placed in JavaHeap, flush into RocksDbState when invoke 
> finishBundle , this can reduce the number of serialization.
> But now FlinkRunner calls the finishBundle every processElement. We need 
> support real Bundle.
> I think we can have the following implementations:
> 1.Invoke finishBundle and next startBundle in {{snapshot}} of Flink. But 
> sometimes this "Bundle" maybe too big. This depends on the user's checkpoint 
> configuration.
> 2.Manually control the size of the bundle. The half-bundle will be flushed to 
> a full-bundle by count or eventTime or processTime or {{snapshot}}. We do not 
> need to wait, just call the startBundle and finishBundle at the right time.



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