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https://issues.apache.org/jira/browse/YARN-802?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13684258#comment-13684258
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Avner BenHanoch commented on YARN-802:
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Thanks for the explanation about YARN. Still this is not enough, for two
reasons:
1. It is true that *usually* "A shuffle consumer instance will only contact one
of the shuffle providers". Still, as written in the quote I pasted , "it should
be possible to fallback to another shuffle on the fly". This means that one
consumer can load another consumer and serve as proxy to the real consumer that
will contact another provider.
2. In a single job there are multiple reducers each with its own shuffle
consumer instance; hence, we have *multiple shuffle consumers per job*. It
should be possible for each consumer to choose its preffered provider based on
memory/network/... condition on its machine regardless of other consumers in
the same job.
> APPLICATION_INIT is never sent to AuxServices other than the builtin
> ShuffleHandler
> -----------------------------------------------------------------------------------
>
> Key: YARN-802
> URL: https://issues.apache.org/jira/browse/YARN-802
> Project: Hadoop YARN
> Issue Type: Bug
> Components: applications, nodemanager
> 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.
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