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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 Sat, 14 Aug 2010 00:16:21 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12898484#action_12898484
] 

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

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

Since my problem is just about lookup of mtime, created a new jira MAPREDUCE-2011.

> 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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