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From "Avner BenHanoch (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-5329) APPLICATION_INIT is never sent to AuxServices other than the builtin ShuffleHandler
Date Wed, 28 Aug 2013 12:46:53 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-5329?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13752353#comment-13752353

Avner BenHanoch commented on MAPREDUCE-5329:

Hi Siddharth,

*Regarding your previous comment:*
Isn't the ShuffleToken already specific to a shuffle provider (specifically an Aux service)
- in terms of YARN

I don’t think there is an architectural reason for having _shuffleToken_ specific per shuffle
provider.  *It is safe and reasonable to have one _shuffleToken_ for all shuffle-providers
and for all shuffle-consumers of a job.*
Looking in the current code, _TaskAttemptImpl_ creates _shuffleToken_ on the fly for shuffle
needs based on the job token and on user credentials.  The _shuffleToken_ is stored in _TokenCache/Credentials
map_ under the general shuffle label _"MapReduceShuffleToken"_.  
Also, in the shuffle-consumer side, _shuffleToken_ is part of the ReduceTask and it is not
specific to a shuffle-consumer in any way.

The only thing that may relate _shuffleToken_ to a specific aux-service is an existing biased
in the current code. The code for serializing/deserializing _shuffleToken_ is located in 2
static methods in the _AuxiliaryService_ class _ShuffleHandler_.  However, I think there is
no real justification for that and it is very easy to move these 2 simple methods to a more
appropriate place like the _Token_ class itself.

*Regarding your current comment:*
If the MR AM knows how to handle multiple services, and informs the NM about all of these,
APPLICATION_INIT should just go out to all of them. Sounds like this jira can be used to fix

I think that sending _APPLICATION_INIT_ message worth an issue for itself and fixing it can
help a lot several aux-services regardless of any additional fix for service port (for example
aux-services that rely on RDMA and do not use TCP at all, or aux-services that can read port
from conf).

The purpose of the suggested new MAPREDUCE issue is one step further - for *configuring multiple
aux-services* with service-port, regardless of shuffle-providers and regardless of _APPLICATION_INIT_.
 Beside, the new issue is blocked on YARN-1065.  Hence, I prefer to fix this little issue
without waiting for a comprehensive fix for all the “neighbor” issues.

Thanks for your help,

> APPLICATION_INIT is never sent to AuxServices other than the builtin ShuffleHandler
> -----------------------------------------------------------------------------------
>                 Key: MAPREDUCE-5329
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5329
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mr-am
>    Affects Versions: 2.0.4-alpha
>            Reporter: Avner BenHanoch
> APPLICATION_INIT is never sent to AuxServices other than the built-in ShuffleHandler.
 This means that 3rd party ShuffleProvider(s) will not be able to function, because APPLICATION_INIT
enables the AuxiliaryService to map jobId->userId. This is needed for properly finding
the MOFs of a job per reducers' requests.
> NOTE: The built-in ShuffleHandler does get APPLICATION_INIT events due to hard-coded
expression in hadoop code. The current TaskAttemptImpl.java code explicitly call: serviceData.put
(ShuffleHandler.MAPREDUCE_SHUFFLE_SERVICEID, ...) and ignores any additional AuxiliaryService.
As a result, only the built-in ShuffleHandler will get APPLICATION_INIT events.  Any 3rd party
AuxillaryService will never get APPLICATION_INIT events.
> I think a solution can be in one of two ways:
> 1. Change TaskAttemptImpl.java to loop on all Auxiliary Services and register each of
them, by calling serviceData.put (…) in loop.
> 2. Change AuxServices.java similar to the fix in: MAPREDUCE-2668  "APPLICATION_STOP is
never sent to AuxServices".  This means that in case the 'handle' method gets APPLICATION_INIT
event it will demultiplex it to all Aux Services regardless of the value in event.getServiceID().
> I prefer the 2nd solution.  I am welcoming any ideas.  I can provide the needed patch
for any option that people like.
> See [Pluggable Shuffle in Hadoop documentation|http://hadoop.apache.org/docs/current/hadoop-mapreduce-client/hadoop-mapreduce-client-core/PluggableShuffleAndPluggableSort.html]

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