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From John Lilley <john.lil...@redpoint.net>
Subject RE: temporary file locations for YARN applications
Date Mon, 21 Oct 2013 15:19:40 GMT
Thanks again.  This gives me a lot of options; we will see what works.

Do you know if there are any permissions issues if we directly access the folders of LOCAL_DIR_ENV?

Regarding LocalDirAllocator, I see its constructor: LocalDirAllocator(String contextCfgItemName)
and a note mentioning that an example of this item is "mapred.local.dir".  Is that the correct
usage, or is there something YARN-generic?


-----Original Message-----
From: Harsh J [mailto:harsh@cloudera.com] 
Sent: Sunday, October 20, 2013 11:58 PM
To: <user@hadoop.apache.org>
Subject: Re: temporary file locations for YARN applications


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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