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https://issues.apache.org/jira/browse/BEAM-9959?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17134407#comment-17134407
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Beam JIRA Bot commented on BEAM-9959:
-------------------------------------
This issue is assigned but has not received an update in 30 days so it has been
labeled "stale-assigned". If you are still working on the issue, please give an
update and remove the label. If you are no longer working on the issue, please
unassign so someone else may work on it. In 7 days the issue will be
automatically unassigned.
> Mistakes Computing Composite Inputs and Outputs
> -----------------------------------------------
>
> Key: BEAM-9959
> URL: https://issues.apache.org/jira/browse/BEAM-9959
> Project: Beam
> Issue Type: Bug
> Components: sdk-go
> Reporter: Robert Burke
> Assignee: Robert Burke
> Priority: P2
> Labels: stale-assigned
>
> The Go SDK uses a Scope object to manage beam Composites.
> A bug was discovered when consuming a PCollection in both the composite that
> created it, and in a separate composite.
> Further, the Go SDK should verify that the root hypergraph structure is a DAG
> and provides a reasonable error. In particular, the leaf nodes of the graph
> could form a DAG, but due to how the beam.Scope object is used, might cause
> the hypergraph to not be a DAG.
> Eg. It's possible to write the following in the Go SDK.
> PTransforms A, B, C and PCollections colA, colB, and Composites a, b.
> A and C are in a, and B are in b.
> A generates colA
> B consumes colA, and generates colB.
> C consumes colA and colB.
> ```
> a := s.Scope(a)
> b := s.Scope(b)
> colA := beam.Impulse(*a*)
> colB := beam.ParDo(*b*, <doFn>, colA)
> beam.ParDo0(*a*, <doFn>, colA, beam.SideInput{colB})
> ```
> If it doesn't already, the Go SDK must emit a clear error, and fail pipeline
> construction.
> If the affected composites are roots in the graph, the cycle prevents being
> able to topologically sort the root ptransforms for the pipeline graph, which
> can adversely affect runners.
> The recommendation is always to wrap uses of scope in functions or other
> scopes to prevent such incorrect constructions.
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