[
https://issues.apache.org/jira/browse/MAPREDUCE-1901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12898376#action_12898376
]
Joydeep Sen Sarma commented on MAPREDUCE-1901:
----------------------------------------------
> if the jar changed resulting in different tasks of the same job getting
> different data rendering debugging impossible!
prior to security related functionality (and even with it if the user is
capricious enough) - i think this was very much possible. the only contract
that the TT's seem to follow today is that the launched task sees the latest
possible version of a required resource (jar/file etc.). there's no contract
that says that each task sees identical version of each resource. the mtime
check only seems to reinforce this notion - that resources could be changing
underneath as the job is running.
that said - there will likely be security holes in our current scheme. we will
post a spec and trunk patch by sometime later today (or weekend) hopefully.
> 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.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
