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From "Koji Noguchi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1901) Jobs should not submit the same jar files over and over again
Date Fri, 13 Aug 2010 16:28:21 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12898300#action_12898300
] 

Koji Noguchi commented on MAPREDUCE-1901:
-----------------------------------------

bq. u would get a trace of all those jars being uploaded to hdfs. it's ridiculous.

For me, that's not of a worry.  It may delay individual job submissions, but the overall load
to the hdfs isn't much.
(at least compared to later phase of hundreds and thousands of tasktrackers looking up mtime
of 'all those jars'.)

> Jobs should not submit the same jar files over and over again
> -------------------------------------------------------------
>
>                 Key: MAPREDUCE-1901
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1901
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>            Reporter: Joydeep Sen Sarma
>         Attachments: 1901.PATCH
>
>
> Currently each Hadoop job uploads the required resources (jars/files/archives) to a new
location in HDFS. Map-reduce nodes involved in executing this job would then download these
resources into local disk.
> In an environment where most of the users are using a standard set of jars and files
(because they are using a framework like Hive/Pig) - the same jars keep getting uploaded and
downloaded repeatedly. The overhead of this protocol (primarily in terms of end-user latency)
is significant when:
> - the jobs are small (and conversantly - large in number)
> - Namenode is under load (meaning hdfs latencies are high and made worse, in part, by
this protocol)
> Hadoop should provide a way for jobs in a cooperative environment to not submit the same
files over and again. Identifying and caching execution resources by a content signature (md5/sha)
would be a good alternative to have available.

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