Krzysztof Trubalski created BEAM-5063:
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Summary: Watermark does not progress for low traffic streams
Key: BEAM-5063
URL: https://issues.apache.org/jira/browse/BEAM-5063
Project: Beam
Issue Type: Bug
Components: io-java-kinesis
Affects Versions: 2.5.0
Reporter: Krzysztof Trubalski
Assignee: Jean-Baptiste Onofré
We have a Dataflow Job copying data from multiple Kinesis streams into Big
Query. Recently we have noticed that the watermark on one of the streams
frequently gets stuck although data from that stream is still being processed
(it progress only when the traffic increases or Dataflow autoscaling feature
kicks in).
Looking at the CloudWatch statistics for the affected stream, it has a really
low traffic rate - only 2 events per minute + 4 events every 5 minutes. After
investigation and consulting the issue with Google's Dataflow Team, it looks
like with such small amount of data on the stream, the function calculating the
watermark in KinesisReader reports progress incorrectly.
>From my initial investigation, I suspect that the MovingFunction used to keep
>track of the watermark in KinesisReader is incorrectly used. In the current
>implementation, min is obtained first and then the significance is checked.
>Since obtaining the min value flushes stale values, the following call to
>significance check always returns false (as it relies on the number of
>samples, and most of them were flushed by get() invocation).
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