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 <[EMAIL PROTECTED]> wrote:
> Any comments/corrections on my understanding on Uber?
> Thanks in advance!
> 2013/11/8 sam liu <[EMAIL PROTECTED]>
> 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 mode):
> - 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
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