Hi
I guess when we call submit() method that in tern call the setUseNewAPI()
method to set the MR2 relevent setting.. here what i found after code walk
through of hadoop
private void setUseNewAPI()
throws IOException
{
int numReduces = conf.getNumReduceTasks();
String oldMapperClass = "mapred.mapper.class";
String oldReduceClass = "mapred.reducer.class";
conf.setBooleanIfUnset("mapred.mapper.new-api",
conf.get(oldMapperClass) == null);
if(conf.getUseNewMapper())
{
String mode = "new map API";
ensureNotSet("mapred.input.format.class", mode);
ensureNotSet(oldMapperClass, mode);
if(numReduces != 0)
ensureNotSet("mapred.partitioner.class", mode);
else
ensureNotSet("mapred.output.format.class", mode);
} else
{
String mode = "map compatability";
ensureNotSet("mapreduce.inputformat.class", mode);
ensureNotSet("mapreduce.map.class", mode);
if(numReduces != 0)
ensureNotSet("mapreduce.partitioner.class", mode);
else
ensureNotSet("mapreduce.outputformat.class", mode);
}
if(numReduces != 0)
{
conf.setBooleanIfUnset("mapred.reducer.new-api",
conf.get(oldReduceClass) == null);
if(conf.getUseNewReducer())
{
String mode = "new reduce API";
ensureNotSet("mapred.output.format.class", mode);
ensureNotSet(oldReduceClass, mode);
} else
{
String mode = "reduce compatability";
ensureNotSet("mapreduce.outputformat.class", mode);
ensureNotSet("mapreduce.reduce.class", mode);
}
}
}
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Raj K Singh
http://in.linkedin.com/in/rajkrrsingh
http://www.rajkrrsingh.blogspot.com
Mobile Tel: +91 (0)9899821370
On Tue, Jun 3, 2014 at 5:34 PM, Michael Segel <[email protected]>
wrote:
> Just a quick question...
>
> Suppose you have a M/R job running.
> How does the Mapper or Reducer task know or find out if its running as a
> M/R 1 or M/R 2 job?
>
> I would suspect the job context would hold that information... but on
> first glance I didn't see it.
> So what am I missing?
>
> Thx
>
> -Mike
>
>
>
