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https://issues.apache.org/jira/browse/MAPREDUCE-2349?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13266293#comment-13266293
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Liyin Liang commented on MAPREDUCE-2349:
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This jira is very meaningful for large, busy cluster.
> speed up list[located]status calls from input formats
> -----------------------------------------------------
>
> Key: MAPREDUCE-2349
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-2349
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: task
> Reporter: Joydeep Sen Sarma
>
> when a job has many input paths - listStatus - or the improved
> listLocatedStatus - calls (invoked from the getSplits() method) can take a
> long time. Most of the time is spent waiting for the previous call to
> complete and then dispatching the next call.
> This can be greatly speeded up by dispatching multiple calls at once (via
> executors). If the same filesystem client is used - then the calls are much
> better pipelined (since calls are serialized) and don't impose extra burden
> on the namenode while at the same time greatly reducing the latency to the
> client. In a simple test on non-peak hours, this resulted in the getSplits()
> time reducing from about 3s to about 0.5s.
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