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https://issues.apache.org/jira/browse/FLINK-2577?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14718460#comment-14718460
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ASF GitHub Bot commented on FLINK-2577:
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Github user rmetzger commented on the pull request:
https://github.com/apache/flink/pull/1060#issuecomment-135761217
+1 to merge
> Watermarks Stall When a Source Finishes Prematurely
> ---------------------------------------------------
>
> Key: FLINK-2577
> URL: https://issues.apache.org/jira/browse/FLINK-2577
> Project: Flink
> Issue Type: Bug
> Components: Streaming
> Affects Versions: 0.10
> Reporter: Aljoscha Krettek
> Assignee: Aljoscha Krettek
> Fix For: 0.10
>
>
> The problem with a streaming source that closes is that downstream operations
> never notice that it is not running anymore and keep waiting for watermarks
> from all upstream operations (including the source). This has the effect that
> watermarks just stop propagating through the topology.
> I think an easy fix is to change sources to emit a last watermark of +Inf
> before closing. Because watermarks are always the minimum of all watermarks
> on the inputs this would have the effect of advancing only depending on the
> other inputs.
> The added benefit would be that once all sources emit a +Inf watermark the
> operator also get's a last +Inf watermark which tells it that all sources are
> done. Right now, streaming operators (and user code) have no way of telling
> if there are going to come elements in the future. This is especially
> problematic in Co-Map (Co-FlatMap) operations where you have one input that
> feeds a hash-table and the other input is elements that you want to stream by
> this hash-table.
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