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MapReduce >> mail # user >> Filesystem closed exception


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Hemanth Yamijala 2013-01-25, 01:26
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Harsh J 2013-01-25, 06:21
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Alejandro Abdelnur 2013-01-30, 18:49
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Re: Filesystem closed exception
FS Caching is enabled on the cluster (i.e. the default is not changed).

Our code isn't actually mapper code, but a standalone java program being
run as part of Oozie. It just seemed confusing and not a very clear
strategy to leave unclosed resources. Hence my suggestion to get an
uncached FS handle for this use case alone. Note, I am not suggesting to
disable FS caching in general.

Thanks
Hemanth
On Thu, Jan 31, 2013 at 12:19 AM, Alejandro Abdelnur <[EMAIL PROTECTED]>wrote:

> Hemanth,
>
> Is FS caching enabled or not in your cluster?
>
> A simple solution would be to modify your mapper code not to close the FS.
> It will go away when the task ends anyway.
>
> Thx
>
>
> On Thu, Jan 24, 2013 at 5:26 PM, Hemanth Yamijala <
> [EMAIL PROTECTED]> wrote:
>
>> Hi,
>>
>> We are noticing a problem where we get a filesystem closed exception when
>> a map task is done and is finishing execution. By map task, I literally
>> mean the MapTask class of the map reduce code. Debugging this we found that
>> the mapper is getting a handle to the filesystem object and itself calling
>> a close on it. Because filesystem objects are cached, I believe the
>> behaviour is as expected in terms of the exception.
>>
>> I just wanted to confirm that:
>>
>> - if we do have a requirement to use a filesystem object in a mapper or
>> reducer, we should either not close it ourselves
>> - or (seems better to me) ask for a new version of the filesystem
>> instance by setting the fs.hdfs.impl.disable.cache property to true in job
>> configuration.
>>
>> Also, does anyone know if this behaviour was any different in Hadoop 0.20
>> ?
>>
>> For some context, this behaviour is actually seen in Oozie, which runs a
>> launcher mapper for a simple java action. Hence, the java action could very
>> well interact with a file system. I know this is probably better addressed
>> in Oozie context, but wanted to get the map reduce view of things.
>>
>>
>> Thanks,
>> Hemanth
>>
>
>
>
> --
> Alejandro
>