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https://issues.apache.org/jira/browse/HADOOP-1338?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12494358
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Devaraj Das commented on HADOOP-1338:
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"This might make more sense for cases where we have two or more waves of
reduces" - should clarify this by saying that, although the first wave of
shuffles is gated by the time the Map phase takes to complete, we should check
whether the subsequent waves of shuffles would gain by this optimization. I
think the first phase of shuffle might also gain to some extent.
> Improve the shuffle phase by using the "connection: keep-alive" and doing
> batch transfers of files
> --------------------------------------------------------------------------------------------------
>
> Key: HADOOP-1338
> URL: https://issues.apache.org/jira/browse/HADOOP-1338
> Project: Hadoop
> Issue Type: Improvement
> Components: mapred
> Reporter: Devaraj Das
> Fix For: 0.14.0
>
>
> We should do transfers of map outputs at the granularity of
> *total-bytes-transferred* rather than the current way of transferring a
> single file and then closing the connection to the server. A single
> TaskTracker might have a couple of map output files for a given reduce, and
> we should transfer multiple of them (upto a certain total size) in a single
> connection to the TaskTracker. Using HTTP-1.1's keep-alive connection would
> help since it would keep the connection open for more than one file transfer.
> We should limit the transfers to a certain size so that we don't hold up a
> jetty thread indefinitely (and cause timeouts for other clients).
> Overall, this should give us improved performance.
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