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https://issues.apache.org/jira/browse/BEAM-11366?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17549002#comment-17549002
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Danny McCormick commented on BEAM-11366:
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This issue has been migrated to https://github.com/apache/beam/issues/20612
> Dataflow and KafkaIO or KinesisIO has erratic watermark progress due to
> ReaderCache timeouts
> --------------------------------------------------------------------------------------------
>
> Key: BEAM-11366
> URL: https://issues.apache.org/jira/browse/BEAM-11366
> Project: Beam
> Issue Type: Bug
> Components: runner-dataflow
> Reporter: Sam Whittle
> Priority: P3
>
> The ReaderCache has a default timeout of 1 minute. If the source is not
> polled within that time, the UnboundedReader is destroyed and will be
> reinitilized from the checkpoint when next polled. This is too short for runs
> where the source is not polled for a while due to other keys to process. In
> particular this seems to affect Streaming engine pipelines with backlog.
> From an initial look, recovery from the Kafka UnboundedReader checkpoint does
> not seem to use the previous watermark for initializing the timestamp policy
> and perhaps the timestamp policy will return unknown watermark if it has not
> yet observed a record.
> So possible fixes would be:
> - make cache timeout configurable, or maybe dynamic, and increase it
> - ensure that KafkaIO and KinesisIO recovery from checkpoints initializes the
> watermark properly so that cache eviction does not matter for watermark
> smoothness
> - ensure that cache eviction happens in the background instead of blocking
> threads acquiring readers which might not expect blocking
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