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From Harsh J <ha...@cloudera.com>
Subject Re: temporary file locations for YARN applications
Date Mon, 21 Oct 2013 05:58:16 GMT
Hi,

MR does use multiple disks when spilling. But the work directory is
also round-robined to spread I/O.

YARN sets an environment property thats a list (comma separated value)
of directories (ApplicationConstants.LOCAL_DIR_ENV) your app container
can together use. Perhaps read it in with
StringUtils.getTrimmedStrings(System.getenv(ApplicationConstants.LOCAL_DIR_ENV));
and then round robin internally over those paths (with free space
handling)?

Perhaps you can even reuse the org.apache.hadoop.fs.LocalDirAllocator
class; which is what MR uses. Its not been declared publicly stable
though, but we can do that over a JIRA.

On Mon, Oct 21, 2013 at 2:05 AM, John Lilley <john.lilley@redpoint.net> wrote:
> Harsh, thanks for the quick response.  These files don't need to be on the DFS (although
we use that too).  These are local files used during sorting, joining, transitive closure.
>
> The task-relative folder might be good enough, but our app *can* make use of multiple
temp folders if they are available.  Our YARN app can be fairly I/O intensive; is it possible
to allocate more than one temp folder on different physical devices?
>
> Or perhaps YARN might help us. Will YARN assign tasks to CWD folders on different disks
so that they do not compete with each other on I/O?
>
> For that matter, where does MR allocate the temporary files generated by Mapper output?
 Presumably MR has the same I/O parallelism requirements that we do.
>
> Thanks
> John
>
>
> -----Original Message-----
> From: Harsh J [mailto:harsh@cloudera.com]
> Sent: Sunday, October 20, 2013 10:49 AM
> To: <user@hadoop.apache.org>
> Subject: Re: temporary file locations for YARN applications
>
> Every container gets its own local work directory (You can use the relative ./) thats
auto-cleaned up at the end of the container's life.
> This is the best place to store the temporary files. This is not something you need custom
configuration for.
>
> Do the files need to be on a distributed FS or a local one?
>
> On Sun, Oct 20, 2013 at 8:54 PM, John Lilley <john.lilley@redpoint.net> wrote:
>> We have a pure YARN application (no MapReduce) that has need to store
>> a significant amount of temporary data.  How can we know the best
>> location for these files?  How can we ensure that our YARN tasks have
>> write access to these locations?  Is this something that must be configured outside
of YARN?
>> Thanks,
>> John
>
> --
> Harsh J



-- 
Harsh J

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