The *mapred*.*tasktracker*.*reduce*.*tasks*.*maximum* parameter sets the
maximum number of reduce tasks that may be run by an individual TaskTracker
server at one time. This is not per job configuration.
he number of map tasks for a given job is driven by the number of input
splits and not by the mapred.map.tasks parameter. For each input split a
map task is spawned. So, over the lifetime of a mapreduce job the number of
map tasks is equal to the number of input splits. mapred.map.tasks is just
a hint to the InputFormat for the number of maps
If you want to set max number of maps or reducers per job then you can set
the hints by using the job object you created
job.setNumMapTasks()
Note this is just a hint and again the number will be decided by the input
split size.
On Tue, Apr 30, 2013 at 3:39 PM, Han JU <ju.han.fe...@gmail.com> wrote:
> Thanks Nitin.
>
> What I need is to set slot only for a specific job, not for the whole
> cluster conf.
> But what I did does NOT work ... Have I done something wrong?
>
>
> 2013/4/30 Nitin Pawar <nitinpawar...@gmail.com>
>
>> The config you are setting is for job only
>>
>> But if you want to reduce the slota on tasktrackers then you will need to
>> edit tasktracker conf and restart tasktracker
>> On Apr 30, 2013 3:30 PM, "Han JU" <ju.han.fe...@gmail.com> wrote:
>>
>>> Hi,
>>>
>>> I want to change the cluster's capacity of reduce slots on a per job
>>> basis. Originally I have 8 reduce slots for a tasktracker.
>>> I did:
>>>
>>> conf.set("mapred.tasktracker.reduce.tasks.maximum", "4");
>>> ...
>>> Job job = new Job(conf, ...)
>>>
>>>
>>> And in the web UI I can see that for this job, the max reduce tasks is
>>> exactly at 4, like I set. However hadoop still launches 8 reducer per
>>> datanode ... why is this?
>>>
>>> How could I achieve this?
>>> --
>>> *JU Han*
>>>
>>> Software Engineer Intern @ KXEN Inc.
>>> UTC - Université de Technologie de Compiègne
>>> * **GI06 - Fouille de Données et Décisionnel*
>>>
>>> +33 0619608888
>>>
>>
>
>
> --
> *JU Han*
>
> Software Engineer Intern @ KXEN Inc.
> UTC - Université de Technologie de Compiègne
> * **GI06 - Fouille de Données et Décisionnel*
>
> +33 0619608888
>
--
Nitin Pawar
