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From "Jonathan Gray (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-5170) Set max map/reduce tasks on a per-job basis, either per-node or cluster-wide
Date Wed, 27 May 2009 02:59:46 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-5170?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Jonathan Gray updated HADOOP-5170:
----------------------------------

    Attachment: tasklimits-v3-0.19.patch

I'm still on 0.19 and really need this patch.

Attached is a patch that applies cleanly to current 0.19 branch.  Note: This removes the unit
test!  I tried to get the test to work in 0.19 but eventually turned to doing manual testing
on my cluster with my jobs.

All my testing shows that the patch works as advertised.

I'm moving this into a busy production system and will report back if there are any issues.

> Set max map/reduce tasks on a per-job basis, either per-node or cluster-wide
> ----------------------------------------------------------------------------
>
>                 Key: HADOOP-5170
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5170
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: mapred
>            Reporter: Jonathan Gray
>            Assignee: Matei Zaharia
>         Attachments: tasklimits-v2.patch, tasklimits-v3-0.19.patch, tasklimits-v3.patch,
tasklimits.patch
>
>
> There are a number of use cases for being able to do this.  The focus of this jira should
be on finding what would be the simplest to implement that would satisfy the most use cases.
> This could be implemented as either a per-node maximum or a cluster-wide maximum.  It
seems that for most uses, the former is preferable however either would fulfill the requirements
of this jira.
> Some of the reasons for allowing this feature (mine and from others on list):
> - I have some very large CPU-bound jobs.  I am forced to keep the max map/node limit
at 2 or 3 (on a 4 core node) so that I do not starve the Datanode and Regionserver.  I have
other jobs that are network latency bound and would like to be able to run high numbers of
them concurrently on each node.  Though I can thread some jobs, there are some use cases that
are difficult to thread (scanning from hbase) and there's significant complexity added to
the job rather than letting hadoop handle the concurrency.
> - Poor assignment of tasks to nodes creates some situations where you have multiple reducers
on a single node but other nodes that received none.  A limit of 1 reducer per node for that
job would prevent that from happening. (only works with per-node limit)
> - Poor mans MR job virtualization.  Since we can limit a jobs resources, this gives much
more control in allocating and dividing up resources of a large cluster.  (makes most sense
w/ cluster-wide limit)

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