[jira] Created: (MAPREDUCE-1901) Jobs should not submit the same jar files over and over again

["Joydeep Sen Sarma (JIRA)" <ji...@apache.org>]

Jobs should not submit the same jar files over and over again
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                 Key: MAPREDUCE-1901
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1901
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
            Reporter: Joydeep Sen Sarma


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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