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From Arun C Murthy <...@hortonworks.com>
Subject Re: About conception and usage of Uber
Date Tue, 12 Nov 2013 02:27:05 GMT
Yes, your understanding is correct. WIth 'uber' mode enabled, you'll run everything within
the container of the AM itself which leads to significantly faster runtimes for 'small' jobs
(we've observed 2x-3x speedup for some jobs).


On Nov 10, 2013, at 5:35 PM, sam liu <samliuhadoop@gmail.com> wrote:

> Any comments/corrections on my understanding on Uber? 
> Thanks in advance!
> 2013/11/8 sam liu <samliuhadoop@gmail.com>
> Hi Experts,
> In previous discussions, I found following descriptions:
> "mapreduce.job.ubertask.enable | (false) | 'Whether to enable the small-jobs "ubertask"
optimization, which runs "sufficiently small" jobs sequentially within a single JVM. "Small"
is defined by the following maxmaps, maxreduces, and maxbytes settings. Users may override
this value.'"
> Basing on above description, I set "mapreduce.job.ubertask.enable" to true and also configured
other uber related parameters, and then I did some practices and have following understanding.

> 1) If I submit a bunch of small MR jobs to Hadoop cluster(each MR job will run in uber
>    - Each MR job corresponds to an application, like application_1383815949546_0006
>    - Each application has its own container, like container_1383815949546_0010_01_000001
>    - When a container launched by nodemanager, it will launch a JVM too. When the container
stops, the JVM will stop as well. A container only has one JVM in its whole life cycle.
>    - Each application_1383815949546_0006 includes some map tasks and reduce tasks
>    - In uber mode, all the map tasks and reduce tasks of application_1383815949546_0006
will be executed in a the same and only container container_1383815949546_0010_01_000001.
It also means that all map tasks and reduce tasks will be executed in a single JVM.
>    - A container could not be shared among different applications(jobs)
> 2) If I submit a bunch of big MR jobs to Hadoop cluster(each MR job will run and NOT
in uber mode):
>    - Each map task and reduce task of application_1383815949546_0006 will be executed
in its own container. It means that application_1383815949546_0006 will have lots of containers.
> I am not sure whether above undertandings are correct or not, so any comments/corrections
will be appreciated! 

Arun C. Murthy
Hortonworks Inc.

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