Improve the shuffle phase by using the "connection: keep-alive" and doing batch
transfers of files
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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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