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https://issues.apache.org/jira/browse/BEAM-6036?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16728439#comment-16728439
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Evgeny commented on BEAM-6036:
------------------------------
This should fix things https://issues.apache.org/jira/browse/BEAM-6261
> How to periodically refresh side inputs
> ---------------------------------------
>
> Key: BEAM-6036
> URL: https://issues.apache.org/jira/browse/BEAM-6036
> Project: Beam
> Issue Type: Bug
> Components: beam-model
> Reporter: Evgeny
> Assignee: Kenneth Knowles
> Priority: Blocker
> Fix For: Not applicable
>
>
> I have followed the example provided here
> [https://cloud.google.com/blog/products/gcp/guide-to-common-cloud-dataflow-use-case-patterns-part-1]
> in the "Pattern: Slowly-changing lookup cache" section. I've converted the
> pseudo-code from the article into this Java code:
> return p
> .apply("GenerateSequence", GenerateSequence.from(0).withRate(1,
> Duration.standardHours(1)))
> .apply("GenerateSequenceWindow",
> Window.<Long>into(new GlobalWindows()).triggering(
> Repeatedly.forever(AfterProcessingTime.pastFirstElementInPane()))
> .discardingFiredPanes())
> .apply("RetrieveKVs",
> ParDo.of(new RetrieveKVs()))
> .apply("ToMap", View.asMap());
> RetrieveKVs() queries BigQuery table and outputs KVs.
> The issue here is that the resulting map mixes up KVs from different periods
> (i.e. the sequence is generated every 1 hour, the resulting map includes KVs
> from 2 adjacent hours).
> In an attempt to solve it I tried using View.asSingleton() instead.
> return p
> .apply("GenerateSequence", GenerateSequence.from(0).withRate(1,
> Duration.standardHours(1)))
> .apply("GenerateSequenceWindow",
> Window.<Long>into(new GlobalWindows()).triggering(
>
> Repeatedly.forever(AfterProcessingTime.pastFirstElementInPane()))
> .discardingFiredPanes())
> .apply("RetrieveMap",
> ParDo.of(new RetrieveMap()))
> .apply("ToMap", View.asSingleton());
> RetrieveMap queries data from BigQuery and outputs the complete map. The
> issue with this is it not only results in flaky tests with the exception 1
> times out of 10:
> Caused by: java.lang.IllegalArgumentException: Empty PCollection accessed as
> a singleton view. Consider setting withDefault to provide a def
> ault value
> but also it doesn't seem to work. In the logs I see the RetrieveMap is called
> every hour, but the pipeline using the side input gets stale data.
> Is there a real working example for how to make a side input refresh
> periodically?
> Related
> https://issues.apache.org/jira/browse/BEAM-6086?page=com.atlassian.jira.plugin.system.issuetabpanels%3Aall-tabpanel
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