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Date: Wed, 9 Jun 2010 01:14:13 -0400 (EDT)
From: "Amareshwari Sriramadasu (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
Subject: [jira] Resolved: (MAPREDUCE-1781) option "-D
 mapred.tasktracker.map.tasks.maximum=1" does not work when no of mappers is
 bigger than no of nodes - always spawns 2 mapers/node
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     [ https://issues.apache.org/jira/browse/MAPREDUCE-1781?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Amareshwari Sriramadasu resolved MAPREDUCE-1781.
------------------------------------------------

    Resolution: Invalid

bq. Regarding the initial problem, I think it would help a lot of people (especially new users) to specify in the config page[ http://hadoop.apache.org/common/docs/current/mapred-default.html ] which parameters are set at startup and which at job runtime.
In branch 0.21, the configuration names are standardized through MAPREDUCE-849. The configuration names with prefix as mapreduce.cluster/mapreduce.jobtracker/mapreduce.tasktracker are server level configurations and need to be setup before the cluster is brought up. The other configurations with prefix mapreduce.job/mapreduce.task/mapreduce.map/mapreduce.reduce are job level configurations. 
Documenting all of them in mapred-default is being tracked in MAPREDUCE-1021.

Closing this as invalid.

> option "-D mapred.tasktracker.map.tasks.maximum=1" does not work when no of mappers is bigger than no of nodes - always spawns 2 mapers/node
> --------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-1781
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1781
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: contrib/streaming
>    Affects Versions: 0.20.2
>         Environment: Debian Lenny x64, and Hadoop 0.20.2, 2GB RAM
>            Reporter: Tudor Vlad
>
> Hello
> I am a new user of Hadoop and I have some trouble using Hadoop Streaming and the "-D mapred.tasktracker.map.tasks.maximum" option. 
> I'm experimenting with an unmanaged application (C++) which I want to run over several nodes in 2 scenarios
> 1) the number of maps (input splits) is equal to the number of nodes
> 2) the number of maps is a multiple of the number of nodes (5, 10, 20, ...
> Initially, when running the tests in scenario 1 I would sometimes get 2 process/node on half the nodes. However I fixed this by adding the optin "-D mapred.tasktracker.map.tasks.maximum=1", so everything works fine.
> In the case of scenario 2 (more maps than nodes) this directive no longer works, always obtaining 2 processes/node. I tested the even with putting maximum=5 and I still get 2 processes/node.
> The entire command I use is:
> /usr/bin/time --format="-duration:\t%e |\t-MFaults:\t%F |\t-ContxtSwitch:\t%w" \
>  /opt/hadoop/bin/hadoop jar /opt/hadoop/contrib/streaming/hadoop-0.20.2-streaming.jar \
>  -D mapred.tasktracker.map.tasks.maximum=1 \
>  -D mapred.map.tasks=30 \
>  -D mapred.reduce.tasks=0 \
>  -D io.file.buffer.size=5242880 \
>  -libjars "/opt/hadoop/contrib/streaming/hadoop-7debug.jar" \
>  -input input/test \
>  -output out1 \
>  -mapper "/opt/jobdata/script_1k" \
>  -inputformat "me.MyInputFormat"
> Why is this happening and how can I make it work properly (i.e. be able to limit exactly how many mappers I can have at 1 time per node)?
> Thank you in advance

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