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From Vinod Kumar Vavilapalli <vino...@hortonworks.com>
Subject Re: scheduler satisfying heterogeneous resource requests at same priority
Date Fri, 04 Jan 2013 04:14:40 GMT
The answer is a combination of what Robert and Bikas mentioned above.

 - Priorities are used to order the scheduling requests.
 - At a given priority, if you have requests of different sizes, it could be looking at the
last request. We can clarify this in docs.

+Vinod Kumar Vavilapalli
Hortonworks Inc.

On Jan 3, 2013, at 3:15 AM, Tsuyoshi OZAWA wrote:

> Sandy, it also depends on the timing. For instance, in MapReduce's case,
> MRAppMaster requests the containers for each task separately. Could you
> explain the timing when you issue each request?
> On Thu, Jan 3, 2013 at 5:52 AM, Robert Evans <evans@yahoo-inc.com> wrote:
>> Mappers and reducers are requested at different priorities.  Reducers have
>> a higher priority. But the AM does not request all of the reducers at
>> once. It waits and will request some at a time until all of the mappers
>> have been satisfied at which point it then requests the rest of the
>> reducers.
>> --Bobby
>> On 1/2/13 2:47 PM, "Sandy Ryza" <sandy.ryza@cloudera.com> wrote:
>>> Thanks for looking into it Bikas.  What you wrote makes sense to me.
>>> You're
>>> right that it's the last request not the largest.  Otherwise, you
>>> summarize
>>> my confusion well - why doesn't AppSchedulingInfo hold a list of
>>> ResourceRequests for each node/priority?
>>> I also don't understand why this hasn't caused a problem already for
>>> mapreduce when mappers and reducers request different amounts of memory.
>>> It must be either because reduces are requested after all map containers
>>> are completed? Or because they're requested at non-overlapping locations?
>>> On Wed, Jan 2, 2013 at 11:04 AM, Bikas Saha <bikas@hortonworks.com>
>> wrote:
>>>> Reading the code seems to suggest that AppSchedulingInfo is not
>>>> preferring
>>>> the larger request. Its simply returning the last request for that
>>>> priority and hostname. So it could be that in your case, the larger
>>>> request is the second request. You could try and make it the first
>>>> request
>>>> and check if you get the same results.
>>>> Wrt, your ResourceRequest question, having a single Resource capability
>>>> simplifies ResourceRequest operations. Having heterogeneous resources is
>>>> allowed by the API by submitting multiple ResourceRequests having
>>>> different Resource capabilities. See the RMContainerRequestor code in
>>>> the
>>>> MR YARN app. Given the above, it looks like the Resource heterogeneity
>>>> is
>>>> lost inside the AppSchedulingInfo and that may be a bug or a conscious
>>>> decision. Looking at folks experienced in that code for an answer. How
>>>> is
>>>> everything working despite this? Perhaps because the applications are
>>>> not
>>>> issuing heterogeneous requests for a given priority and location.
>>>> Secondly, the * catch all is always around to save the day.
>>>> Let me know if this makes sense. I may have missed stuff.
>>>> -----Original Message-----
>>>> From: Sandy Ryza [mailto:sandy.ryza@cloudera.com]
>>>> Sent: Friday, December 28, 2012 4:46 PM
>>>> To: yarn-dev@hadoop.apache.org
>>>> Subject: scheduler satisfying heterogeneous resource requests at same
>>>> priority
>>>> I am trying to understand how YARN schedulers are able to satisfy
>>>> smaller
>>>> requests while larger requests are outstanding (per YARN-289).
>>>> Consider the following situation:
>>>> An application submits two requests - one for a container with 1024 MB
>>>> and
>>>> one for a container with 2048 MB.  1024 MB frees up on a node.  The
>>>> scheduler should (or might wish to) place the smaller container on the
>>>> node, instead of placing a reservation for the larger one.
>>>> However, currently, if I understand correctly, the larger request is
>>>> always serviced first.  AppSchedulingInfo, which is used by all the
>>>> schedulers to find a container request when space becomes available,
>>>> stores a map of priorities to maps of node/rack/* to ResourceRequests.
>>>> A
>>>> ResourceRequest contains a single Resource (capability), and the number
>>>> of
>>>> containers.  Why does a ResourceRequest not allow for heterogeneous
>>>> containers.  Is this just not supported yet because it hasn't been
>>>> needed
>>>> yet?  Or is there a more fundamental reason I'm missing about why it
>>>> doesn't make sense?
>>>> many thanks for any guidance,
>>>> Sandy
> -- 
> OZAWA Tsuyoshi

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