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https://issues.apache.org/jira/browse/SPARK-20560?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15993008#comment-15993008
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Steve Loughran commented on SPARK-20560:
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{{FileSystem.getFileBlockLocations(path)}} is only invoked from from
{{HdfsUtils.getFileSegmentLocations}}, and used as a source of data for
{{RDD.preferredLocations}}
I don't see anything explicit through the code that detects & reacts to the FS
call returning localhost; I'll do some test downstream to see what surfaces
against S3. Unless the scheduler has some explicit "localhost -> anywhere" map,
it might make sense for HdfsUtils.getFileSegmentLocation to downgrade
"localhost" to None, on the basis that in a cluster FS, the data clearly
doesn't know where it is.
> Review Spark's handling of filesystems returning "localhost" in
> getFileBlockLocations
> -------------------------------------------------------------------------------------
>
> Key: SPARK-20560
> URL: https://issues.apache.org/jira/browse/SPARK-20560
> Project: Spark
> Issue Type: Bug
> Components: Scheduler
> Affects Versions: 2.1.0
> Reporter: Steve Loughran
> Priority: Minor
>
> Some filesystems (S3a, Azure WASB) return "localhost" as the response to
> {{FileSystem.getFileBlockLocations(path)}}. If this is then used as the
> preferred host when scheduling work, there's a risk that work will be queued
> on one host, rather than spread across the cluster.
> HIVE-14060 and TEZ-3291 have both seen it in their schedulers.
> I don't know if Spark does it, someone needs to look at the code, maybe write
> some tests
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