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https://issues.apache.org/jira/browse/BEAM-10517?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17159492#comment-17159492
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Kenneth Knowles commented on BEAM-10517:
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[~robinyqiu] since BEAM-10470 was a null pointer exception in the DirectRunner,
I chose to tackle the flake by looking at the errors that show up in checker,
BEAM-10518. There were many true errors, which I will post a PR for soon.
One important one is that it seems in FinishBundle of the precombine stage, it
traverses the keys of an accumulator map. For combinefns where AccumT can be
nullable, the null accumulators will be skipped. It is clearly wrong. It may
affect zetasketch.
> DirectRunner drops null accumulators in multi-step combine
> ----------------------------------------------------------
>
> Key: BEAM-10517
> URL: https://issues.apache.org/jira/browse/BEAM-10517
> Project: Beam
> Issue Type: Bug
> Components: runner-direct
> Reporter: Kenneth Knowles
> Assignee: Kenneth Knowles
> Priority: P1
>
> When outputting accumulators in pre-combine, the direct runner iterates over
> a map of accumulators. However, since an accumulator can be null (such as in
> zetasketch) these accumulators will not be output.
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