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Date: Tue, 18 Nov 2008 16:51:44 -0800 (PST)
From: "Runping Qi (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-1338) Improve the shuffle phase by using
 the "connection: keep-alive" and doing batch transfers of files
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    [ https://issues.apache.org/jira/browse/HADOOP-1338?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12648847#action_12648847 ] 

Runping Qi commented on HADOOP-1338:
------------------------------------

With multiple mapper ids, the the jetty of the TT can fulfill the multiple segments request by reading the map output file sequentially.
If you just use Keep-Alive, you cannot perform such an optimization.

> 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 Core
>          Issue Type: Improvement
>          Components: mapred
>            Reporter: Devaraj Das
>
> 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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