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MapReduce >> mail # dev >> Reducers are launched after jobClient is exited.


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Re: Reducers are launched after jobClient is exited.
MapReduce AppMaster and YARN at large use asynchronous event handling inside the JVM and so you may run into race conditions like this.

Even otherwise, doing this in a deterministic manner is better achieved by overriding your OutputCommitter. Job output commit/abort happens only once.

+Vinod

On Jan 28, 2014, at 7:06 PM, Rohith Sharma K S <[EMAIL PROTECTED]> wrote:

> Hi All ,
>
>             I ran job with 1 Map and 1 Reducers ( mapreduce.job.reduce.slowstart.completedmaps=1 ).  Map failed ( because of error in Mapper implementation), but still Reducers are launched by applicationMaster.  These reducers killed by applicationMaster while
>
> stopping RMCommunicator service.
>
>
> 1.       Why Reducers are launching after job is finished.? ( Is this is bug in MR? )
>
>
>
> Our use case is when job is finished(succeeded/failed),client program delete the JobOutput directory. Here, jobclient exit immediately after jobStatus is set. ( in below log, at 2014-01-23 07:34:43,166)
>
>
>
> But , in the below log as mentioned reducers are launched later , Reducer temporary directory and files are created(_temporary). These files left in hdfs undeleted forever.
>
> Kindly suggest your thoughts, how we can handle this situation?
>
>
>
> 2014-01-23 07:34:43,151 INFO [AsyncDispatcher event handler] org.apache.hadoop.mapreduce.v2.app.job.impl.TaskImpl: task_1389970937094_0047_m_000000 Task Transitioned from RUNNING to FAILED
> 2014-01-23 07:34:43,151 INFO [AsyncDispatcher event handler] org.apache.hadoop.mapreduce.v2.app.job.impl.JobImpl: Num completed Tasks: 1
> 2014-01-23 07:34:43,151 INFO [AsyncDispatcher event handler] org.apache.hadoop.mapreduce.v2.app.job.impl.JobImpl: Job failed as tasks failed. failedMaps:1 failedReduces:0
> 2014-01-23 07:34:43,153 INFO [AsyncDispatcher event handler] org.apache.hadoop.mapreduce.v2.app.job.impl.JobImpl: job_1389970937094_0047Job Transitioned from RUNNING to FAIL_ABORT
> 2014-01-23 07:34:43,153 INFO [CommitterEvent Processor #0] org.apache.hadoop.mapreduce.v2.app.commit.CommitterEventHandler: Processing the event EventType: JOB_ABORT
> 2014-01-23 07:34:43,166 INFO [AsyncDispatcher event handler] org.apache.hadoop.mapreduce.v2.app.job.impl.JobImpl: job_1389970937094_0047Job Transitioned from FAIL_ABORT to FAILED
> ...............
> ...............
> 2014-01-23 07:34:43,707 INFO [RMCommunicator Allocator] org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator: Before Scheduling: PendingReds:1 ScheduledMaps:0 ScheduledReds:0 AssignedMaps:1 AssignedReds:0 CompletedMaps:1 CompletedReds:0 ContAlloc:4 ContRel:0 HostLocal:1 RackLocal:0
> 2014-01-23 07:34:43,709 INFO [RMCommunicator Allocator] org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator: Recalculating schedule, headroom=12288
> 2014-01-23 07:34:43,709 INFO [RMCommunicator Allocator] org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator: Reduce slow start threshold reached. Scheduling reduces.
> 2014-01-23 07:34:43,709 INFO [RMCommunicator Allocator] org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator: All maps assigned. Ramping up all remaining reduces:1
> ...............
> ...............
> 2014-01-23 07:34:45,714 INFO [RMCommunicator Allocator] org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator: Got allocated containers 1
> 2014-01-23 07:34:45,714 INFO [RMCommunicator Allocator] org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator: Assigned to reduce
> 2014-01-23 07:34:45,714 INFO [RMCommunicator Allocator] org.apache.hadoop.mapreduce.v2.app.rm.RMContainerAllocator: Assigned container container_1389970937094_0047_01_000006 to attempt_1389970937094_0047_r_000000_0
> ...............
> ...............
> 2014-01-23 07:34:45,724 INFO [AsyncDispatcher event handler] org.apache.hadoop.mapreduce.v2.app.job.impl.TaskAttemptImpl: attempt_1389970937094_0047_r_000000_0 TaskAttempt Transitioned from UNASSIGNED to ASSIGNED
> 2014-01-23 07:34:45,725 INFO [ContainerLauncher #8] org.apache.hadoop.mapreduce.v2.app.launcher.ContainerLauncherImpl: Processing the event EventType: CONTAINER_REMOTE_LAUNCH for container container_1389970937094_0047_01_000006 taskAttempt attempt_1389970937094_0047_r_000000_0
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