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https://issues.apache.org/jira/browse/MAPREDUCE-1901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12891812#action_12891812
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Arun C Murthy commented on MAPREDUCE-1901:
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Joydeep - Maybe we are talking past each other, yet ...
The DistributedCache _already_ tracks mtimes for files. Each TT, via the
DistributedCache, localizes the file based on <absolute-path-on-hdfs, mtime>.
This seems sufficient for the use case as I understand it.
Here is the flow:
Admin installs pig/hive on hdfs:
/share/hive/v1/hive.jar
/share/hive/v2/hive.jar
The pig/hive framework, in fact, any MR job then does:
JobConf job = new JobConf();
job.setRemoteJar(new Path("/share/hive/v1/hive.jar")
JobConf.submitJob(job);
That's it. The JobClient has the smarts to use
DistributedCache.addArchiveToClassPath as the implementation of
JobConf.setRemoteJar.
If you want a new version of hive.jar, you change hive to use
/share/hive/v2/hive.jar.
What am I missing here?
> 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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