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MapReduce, mail # user - dynamically resizing the Hadoop cluster?


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Re: dynamically resizing the Hadoop cluster?
Ravi Prakash 2013-10-24, 20:51
Hi Nan!

If the task trackers stop heartbeating back to the JobTracker, the JobTracker will mark them as dead and reschedule the tasks which were running on that TaskTracker. Admittedly there is some delay between when the TaskTrackers stop heartbeating back and when the JobTracker marks them dead. This is controlled by the mapred.tasktracker.expiry.interval parameter (I'm assuming you are using Hadoop 1.x)

HTH
Ravi

On Thursday, October 24, 2013 1:21 PM, Nan Zhu <[EMAIL PROTECTED]> wrote:
 
Hi, Ravi,

Thank you for the reply

Actually I'm not running HDFS on EC2, instead I use S3 to store data

I'm curious about that, if some nodes are decommissioned, the JobTracker will deal those tasks which originally ran on them as "too slow" (since no progress for a long time) so to run speculative execution OR it directly treats them as "belonging to a running Job and ran on a dead TaskTracker"?

Best,

Nan

On Thu, Oct 24, 2013 at 2:04 PM, Ravi Prakash <[EMAIL PROTECTED]> wrote:

Hi Nan!
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>Usually nodes are decommissioned slowly over some period of time so as not to disrupt the running jobs. When a node is decommissioned, the NameNode must re-replicate all under-replicated blocks. Rather than suddenly remove half the nodes, you might want to take a few nodes offline at a time. Hadoop should be able to handle rescheduling tasks on nodes no longer available (even without speculative execution. Speculative execution is for something else).
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>HTH
>Ravi
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>On Wednesday, October 23, 2013 10:26 PM, Nan Zhu <[EMAIL PROTECTED]> wrote:
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>Hi, all
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>I’m running a Hadoop cluster on AWS EC2, 
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>I would like to dynamically resizing the cluster so as to reduce the cost, is there any solution to achieve this? 
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>E.g. I would like to cut the cluster size with a half, is it safe to just shutdown the instances (if some tasks are just running on them, can I rely on the speculative execution to re-run them on the other nodes?)
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>I cannot use EMR, since I’m running a customized version of Hadoop 
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>Best,
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>-- 
>Nan Zhu
>School of Computer Science,
>McGill University
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--

Nan Zhu
School of Computer Science, 
McGill University
E-Mail: [EMAIL PROTECTED]