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https://issues.apache.org/jira/browse/TINKERPOP-2393?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17188712#comment-17188712
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Stephen Mallette commented on TINKERPOP-2393:
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> But now I noticed that currently BranchStep determines if it has a barrier
> during construction
I did a few tests and that looks like a bug. It definitely doesn't take into
account the possibility of a {{TraversalStrategy}} adding in a {{Barrier}}. I
think that definitely needs to get fixed. Not sure if we just cut/paste that
block of code to {{standardAlgorithm()}} as-is though. Perhaps you could come
up with a way to make it so that we only test
{{getStepsOfAssignableClassRecursively(Barrier.class, traversalOption)}} once
per child traversal and avoid it happening once per call to
{{standardAlgorithm()}}?
> BranchStep should respect the barrier size of BarrierStep when calling
> applyCurrentTraverser
> --------------------------------------------------------------------------------------------
>
> Key: TINKERPOP-2393
> URL: https://issues.apache.org/jira/browse/TINKERPOP-2393
> Project: TinkerPop
> Issue Type: Improvement
> Components: process
> Affects Versions: 3.4.7
> Reporter: Norio Akagi
> Priority: Minor
>
> Right now in BranchStep, if children contain a BarrierStep it keeps calling
> applyCurrentTraverser until this.starts is exhausted.
> [https://github.com/apache/tinkerpop/blob/534746b6019d0775e628375a3dfeba8a18df90fe/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/branch/BranchStep.java#L139-L140]
> This means the child step may hold all upstream solutions in memory at once,
> and potentially memory usage is bloated.
> I think here we can change so that BarrierStep can have a method like
> getMaxBarrierSize, and BranchStep examines the size of barrier that child
> steps can handle at once then break the while loop either when
> `this.starts.hasNext` becomes false or we exceed the barrier size to save the
> potential memory consumption.
>
> When there are multiple barrier steps as children, we may pick either max or
> min among them.
> I am happy to implement this, but please let me know if you have any comments
> or concerns on this change.
> Thanks
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