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https://issues.apache.org/jira/browse/MAPREDUCE-1207?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12895079#action_12895079
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Dick King commented on MAPREDUCE-1207:
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{{TaskRunner.java}} :

API nomenclature: {{MAPRED_MAP_ADMIN_JAVA_OPTS}} etc. is a property that 
contains options, not a set of options like {{DEFAULT_MAPRED_ADMIN_JAVA_OPTS}} 
, and should probably be named {{MAP_ADMIN_JAVA_OPTS_PROPNAME}} .  There should 
probably be such a property for mapred as well as the two separate properties 
for map and reduce.

funny return value: {{getVMEnvironment}} [and after the patch, 
{{setEnvFromInputString}} ] only ever returns its first parameter, 
{{errorInfo}} , if it returns at all.  The return value is certainly not 
pulling its weight, and the method should be {{void}} .

functionality lack: Environment value substitution is extremely specialized.  
It can basically only handle expansions to path-like environment variables.  

The original code had this property, but with the new code it looks like we 
should to be able to handle more cases.  In particular, 
{{updateUserLoginEnv(...) }} sets several environment variables such as 
{{USER}} .  The administrator is likely to want to be able to expand {{$USER}} 
in a new environment variable value [ie., perhaps a path name].

{{TestTaskEnvironment.java}}

Environment variable substitution is not tested, even the limited version that 
we support.

> Allow admins to set java options for map/reduce tasks
> -----------------------------------------------------
>
>                 Key: MAPREDUCE-1207
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1207
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: client
>            Reporter: Arun C Murthy
>            Assignee: Krishna Ramachandran
>         Attachments: mapred-1207.patch
>
>
> It will be useful for allow cluster-admins to set some java options for child 
> map/reduce tasks. 
> E.g. We've had to ask users to set -Djava.net.preferIPv4Stack=true in their 
> jobs, it would be nice to do it for all users in such scenarios even when 
> people override mapred.child.{map|reduce}.java.opts but forget to add this.

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