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From prasenjit mukherjee <pmukher...@quattrowireless.com>
Subject Re: duplicate tasks getting started/killed
Date Wed, 10 Feb 2010 02:52:40 GMT
Any thoughts on this problem ? I am using a DEFINE command ( in PIG )
and hence the actions are not idempotent. Because of which duplicate
execution does have an affect on my results. Any way to overcome that
?

On Tue, Feb 9, 2010 at 9:26 PM, prasenjit mukherjee
<pmukherjee@quattrowireless.com> wrote:
> But the second attempted job got killed even before the first one was
> completed. How can we explain that.
>
> On Tue, Feb 9, 2010 at 7:38 PM, Eric Sammer <eric@lifeless.net> wrote:
>> Prasen:
>>
>> This is most likely speculative execution. Hadoop fires up multiple
>> attempts for the same task and lets them "race" to see which finishes
>> first and then kills the others. This is meant to speed things along.
>>
>> Speculative execution is on by default, but can be disabled. See the
>> configuration reference for mapred-*.xml.
>>
>> On 2/9/10 9:03 AM, prasenjit mukherjee wrote:
>>> Sometimes for the same task I see that a duplicate task gets run on a
>>> different machine and gets killed later. Not always but sometimes. Any
>>> reason why duplicate tasks get run. I thought tasks are duplicated
>>> only if  either the first attempt exits( exceptions etc ) or  exceeds
>>> mapred.task.timeout. In this case none of them happens. As can be seen
>>> from timestamp, the second attempt starts even though the first
>>> attempt is still running ( only for 1 minute ).
>>>
>>> Any explanation ?
>>>
>>> attempt_201002090552_0009_m_000001_0
>>>     /default-rack/ip-10-242-142-193.ec2.internal
>>>     SUCCEEDED
>>>     100.00%
>>>     9-Feb-2010 07:04:37
>>>     9-Feb-2010 07:07:00 (2mins, 23sec)
>>>
>>> attempt_201002090552_0009_m_000001_1
>>>     Task attempt: /default-rack/ip-10-212-147-129.ec2.internal
>>>     Cleanup Attempt: /default-rack/ip-10-212-147-129.ec2.internal
>>>     KILLED
>>>     100.00%
>>>     9-Feb-2010 07:05:34
>>>     9-Feb-2010 07:07:10 (1mins, 36sec)
>>>
>>>  -Prasen
>>>
>>
>>
>> --
>> Eric Sammer
>> eric@lifeless.net
>> http://esammer.blogspot.com
>>
>

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