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https://issues.apache.org/jira/browse/FLINK-18235?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17688356#comment-17688356
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Dian Fu commented on FLINK-18235:
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{quote} Basically, the Python Operator would have to always wait until receives
a flags/markers "started emitting results for record N" and "finished emitting
results for record N", tracking whether we are in a middle of emitting results
from flat map. {quote}
This is not true. There is no end flag/marker for flat map. Although we could
add such flags for flat map if needed, however, it may be difficult or even
impossible to introduce such a flag for all kinds of operators, e.g. window
operator.
> Improve the checkpoint strategy for Python UDF execution
> --------------------------------------------------------
>
> Key: FLINK-18235
> URL: https://issues.apache.org/jira/browse/FLINK-18235
> Project: Flink
> Issue Type: Improvement
> Components: API / Python
> Reporter: Dian Fu
> Priority: Not a Priority
> Labels: auto-deprioritized-major, stale-assigned
>
> Currently, when a checkpoint is triggered for the Python operator, all the
> data buffered will be flushed to the Python worker to be processed. This will
> increase the overall checkpoint time in case there are a lot of elements
> buffered and Python UDF is slow. We should improve the checkpoint strategy to
> improve this. One way to implement this is to control the number of data
> buffered in the pipeline between Java/Python processes, similar to what
> [FLIP-183|https://cwiki.apache.org/confluence/display/FLINK/FLIP-183%3A+Dynamic+buffer+size+adjustment]
> does to control the number of data buffered in the network. We can also let
> users to config the checkpoint strategy if needed.
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