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From "Sadayuki Furuhashi (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (YARN-4039) New AM instances waste resource by waiting only for resource availability when all available resources are already used
Date Mon, 10 Aug 2015 07:14:45 GMT

     [ https://issues.apache.org/jira/browse/YARN-4039?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Sadayuki Furuhashi updated YARN-4039:
-------------------------------------
    Attachment: YARN-4039.1.patch

> New AM instances waste resource by waiting only for resource availability when all available
resources are already used
> -----------------------------------------------------------------------------------------------------------------------
>
>                 Key: YARN-4039
>                 URL: https://issues.apache.org/jira/browse/YARN-4039
>             Project: Hadoop YARN
>          Issue Type: Improvement
>          Components: fairscheduler
>    Affects Versions: 2.4.0, 2.5.0, 2.6.0, 2.7.0
>            Reporter: Sadayuki Furuhashi
>         Attachments: YARN-4039.1.patch
>
>
> New AM instances waste resource by waiting only for resource availability when all available
resources are already used
> Problem:
> In FairScheduler, maxRunningApps doesn't work well if we can't predict size of an application
in a queue because small maxRunningApps can't use all resources if many small applications
are issued, where large maxRunningApps wastes resources if large applications run.
> Background:
> We're using FairScheduler. In following scenario, AM instances wastes resources significantly:
> * A queue has X MB of capacity.
> * An application requests 32 containers where a container requires (X / 32) MB of memory
> ** In this case, a single application occupies entire resource of the queue.
> * Many those applications are issued (10 applications)
> * Ideal behavior is that applications run one by one to maximize throughput.
> * However, all applications run simultaneously. As the result, AM instances occupy resources
and prevent other tasks from starting. At worst case, most of resources are occupied by waiting
AMs and applications progress very slowly.
> A solution is setting maxRunningApps to 1 or 2. However, it doesn't work well if following
workload exists at the same queue:
> * An application requests 2 containers where a container requires (X / 32) MB of memory
> * Many those applications are issued (say, 10 applications)
> * Ideal behavior is that all applications run simultaneously to maximize concurrency
and throughput.
> * However, number of applications are limited by maxRunningApps. At worst case, most
of resources are idling.
> This problem happens especially with Hive because we can't estimate size of a MapReduce
application.
> Solution:
> AM doesn't have to start if there are waiting resource requests because the AM can't
grant resource requests even if it starts.
> Patch:
> I attached a patch that implements this behavior. But this implementation has this trade-off:
> * When AM is registered to FairScheduler, its demand is 0 because even AM attempt is
not created. Starting this AM doesn't change resource demand of a queue. So, if many AMs are
issued to a queue at the same time, all AMs will be RUNNING. But we want to prevent it.
> * When a AM starts, demand of the AM is only AM attempt. Then AM requires more resources.
Until AM requires resources, demand of the queue is low. But starting AM during this time
will start unnecessary AMs. 
> * So, this patch doesn't start immediately when AM is registered. Instead, it starts
AM only every continuous-scheduling-sleep-ms.
> * Setting large continuous-scheduling-sleep-ms will prevent wasting AMs. But increases
latency.
> Therefore, this patch is enabled only if new option "demand-block-am-enabled" is true.



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