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https://issues.apache.org/jira/browse/SPARK-17648?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15517063#comment-15517063
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Sean Owen commented on SPARK-17648:
-----------------------------------
We recently cleaned up a lot of other instances of this type of thing in
https://issues.apache.org/jira/browse/SPARK-17480. A possibly better solution
is to just iterate over the thing rather than index by position, if possible.
> TaskSchedulerImpl.resourceOffers should take an IndexedSeq, not a Seq
> ---------------------------------------------------------------------
>
> Key: SPARK-17648
> URL: https://issues.apache.org/jira/browse/SPARK-17648
> Project: Spark
> Issue Type: Improvement
> Components: Scheduler, Spark Core
> Affects Versions: 2.0.0
> Reporter: Imran Rashid
> Assignee: Imran Rashid
> Priority: Minor
>
> {{TaskSchedulerImpl.resourceOffer}} takes in a {{Seq[WorkerOffer]}}.
> however, later on it indexes into this by position. If you don't pass in an
> {{IndexedSeq}}, this turns an O(n) operation in an O(n^2) operation.
> In practice, this isn't an issue, since just by chance the important places
> this is called, the datastructures happen to already be {{IndexedSeq}}s. But
> we ought to tighten up the types to make this more clear. I ran into this
> while doing some performance tests on the scheduler, and performance was
> terrible when I passed in a {{Seq}} and even a few hundred offers were
> scheduled very slowly.
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