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https://issues.apache.org/jira/browse/HADOOP-12878?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15324313#comment-15324313
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Thomas Demoor commented on HADOOP-12878:
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[~cnauroth]: I assumed this would be used as follows: by having
{{fs.wasb/s3a.block.location.impersonatedhost=host1,host2,...,host50}} you
would impersonate the block to be local on all nodes, the scheduler would then
be offered options. An optimization would be to return 5 random hosts.
[~dweeks]: Thanks for your interest!
* The current s3a implementation causes scheduling delays as it declares
localhost as the only locality for all blocks.
* The proposed solution can indeed be suboptimal under load but it's always an
improvement over the current situation
* I agree that using "*" woud be easier and more correct but I think
[[email protected]] might have a point. Testing...
* Returning the s3 endpoint so things are always off-rack seems like an
interesting idea. Testing...
[~PieterReuse] has verified that what I originally proposed speeds things up.
We are checking if any of Daniel's proposals would work out as well. Expect an
update next week.
> 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
> Affects Versions: 2.8.0
> 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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