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https://issues.apache.org/jira/browse/HADOOP-12878?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15240971#comment-15240971
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Steve Loughran commented on HADOOP-12878:
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I like your idea of picking randomly; if you really wanted to be clever you''d
use rack topology, but I don't see that would gain much. This is about
distribution of workload. Provided the returned values were sufficiently
random, it would even out.
Can I propose the code for this being entirely self contained; something that
s3a can delegate too. This would allow the test to be isolated in a simple unit
test, and the code reusable elsewhere
> Impersonate hosts in s3a for better data locality handling
> ----------------------------------------------------------
>
> Key: HADOOP-12878
> URL: https://issues.apache.org/jira/browse/HADOOP-12878
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Reporter: Thomas Demoor
> Assignee: Thomas Demoor
>
> Currently, {{localhost}} is passed as locality for each block, causing all
> blocks involved in job to initially target the same node (RM), before being
> moved by the scheduler (to a rack-local node). This reduces parallelism for
> jobs (with short-lived mappers).
> We should mimic Azures implementation: a config setting
> {{fs.s3a.block.location.impersonatedhost}} where the user can enter the list
> of hostnames in the cluster to return to {{getFileBlockLocations}}.
> Possible optimization: for larger systems, it might be better to return N
> (5?) random hostnames to prevent passing a huge array (the downstream code
> assumes size = O(3)).
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