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Date: Thu, 5 May 2016 18:26:13 +0000 (UTC)
From: "Wangda Tan (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
Message-ID: <JIRA.12905705.1445062954000.120723.1462472773090@Atlassian.JIRA>
In-Reply-To: <JIRA.12905705.1445062954000@Atlassian.JIRA>
References: <JIRA.12905705.1445062954000@Atlassian.JIRA> <JIRA.12905705.1445062954690@arcas>
Subject: [jira] [Updated] (MAPREDUCE-6514) Job hangs as ask is not updated
 after ramping down of all reducers
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archived-at: Thu, 05 May 2016 18:26:15 -0000


     [ https://issues.apache.org/jira/browse/MAPREDUCE-6514?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wangda Tan updated MAPREDUCE-6514:
----------------------------------
    Status: Patch Available  (was: Open)

> Job hangs as ask is not updated after ramping down of all reducers
> ------------------------------------------------------------------
>
>                 Key: MAPREDUCE-6514
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6514
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: applicationmaster
>    Affects Versions: 2.7.1
>            Reporter: Varun Saxena
>            Assignee: Varun Saxena
>            Priority: Critical
>         Attachments: MAPREDUCE-6514.01.patch, MAPREDUCE-6514.02.patch
>
>
> In RMContainerAllocator#preemptReducesIfNeeded, we simply clear the scheduled reduces map and put these reducers to pending. This is not updated in ask. So RM keeps on assigning and AM is not able to assign as no reducer is scheduled(check logs below the code).
> If this is updated immediately, RM will be able to schedule mappers immediately which anyways is the intention when we ramp down reducers.
> Scheduler need not allocate for ramped down reducers
> This if not handled can lead to map starvation as pointed out in MAPREDUCE-6513
> {code}
>  LOG.info("Ramping down all scheduled reduces:"
>             + scheduledRequests.reduces.size());
>         for (ContainerRequest req : scheduledRequests.reduces.values()) {
>           pendingReduces.add(req);
>         }
>         scheduledRequests.reduces.clear();
> {code}
> {noformat}
> 2015-10-13 04:55:04,912 INFO [RMCommunicator Allocator] org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator: Container not assigned : container_1437451211867_1485_01_000215
> 2015-10-13 04:55:04,912 INFO [RMCommunicator Allocator] org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator: Cannot assign container Container: [ContainerId: container_1437451211867_1485_01_000216, NodeId: hdszzdcxdat6g06u04p:26009, NodeHttpAddress: hdszzdcxdat6g06u04p:26010, Resource: <memory:4096, vCores:1>, Priority: 10, Token: Token { kind: ContainerToken, service: 10.2.33.236:26009 }, ] for a reduce as either  container memory less than required 4096 or no pending reduce tasks - reduces.isEmpty=true
> 2015-10-13 04:55:04,912 INFO [RMCommunicator Allocator] org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator: Container not assigned : container_1437451211867_1485_01_000216
> 2015-10-13 04:55:04,912 INFO [RMCommunicator Allocator] org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator: Cannot assign container Container: [ContainerId: container_1437451211867_1485_01_000217, NodeId: hdszzdcxdat6g06u06p:26009, NodeHttpAddress: hdszzdcxdat6g06u06p:26010, Resource: <memory:4096, vCores:1>, Priority: 10, Token: Token { kind: ContainerToken, service: 10.2.33.239:26009 }, ] for a reduce as either  container memory less than required 4096 or no pending reduce tasks - reduces.isEmpty=true
> {noformat}


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