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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-195) transfer map output transfer with http instead of rpc
Date Thu, 11 May 2006 16:03:05 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-195?page=comments#action_12379092 ] 

Doug Cutting commented on HADOOP-195:
-------------------------------------

Everything we're now seeing is consistent with the inter-rack switches being the primary bottleneck.
 With 188 nodes sharing a 1Gb/s backbone, there's only 600KB/s per node.  We're seeing 10
80kB files transferred per second, or 800kB/second, slightly higher, since some files are
already on the same rack.

Instead of caching temp files in RAM we can instead try to transfer files soon after they
are generated and to process them on the remote end soon after they are recieved.  That way
we can benefit from the kernel's cache, getting performance similar to what we'd see if we
cached them ourselves.

> transfer map output transfer with http instead of rpc
> -----------------------------------------------------
>
>          Key: HADOOP-195
>          URL: http://issues.apache.org/jira/browse/HADOOP-195
>      Project: Hadoop
>         Type: Improvement

>   Components: mapred
>     Versions: 0.2
>     Reporter: Owen O'Malley
>     Assignee: Owen O'Malley
>      Fix For: 0.3
>  Attachments: data-transfer-chart.pdf, netstat.log, netstat.xls
>
> The data transfer of the map output should be transfered via http instead rpc, because
rpc is very slow for this application and the timeout behavior is suboptimal. (server sends
data and client ignores it because it took more than 10 seconds to be received.)

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