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From Bertrand Dechoux <decho...@gmail.com>
Subject Re: What is the difference between Rack-local map tasks and Data-local map tasks?
Date Sun, 07 Oct 2012 19:31:59 GMT
Basically, more replicas.

The second solution would be to use a 'smarter' scheduler. In theory, the
jobtracker should be able to say "postpone this task until a data-local
task can be created". But I don't think any stable and public available
scheduler do that at the moment. This would allow you to have less traffic
but the whole job might be slower due to the wait. It might be a good trade
if you have multiple jobs running at the same time and if your hot data is
uniformly distributed. But in practice this is of course not always the
case and you also need to consider sla for the users so the whole is not



On Sun, Oct 7, 2012 at 5:28 PM, centerqi hu <centerqi@gmail.com> wrote:

> Very good explanation,
> If there is a way to reduce Rack-local map tasks
> but can increase the Data-local map tasks ,
> Whether to increase performance?
> 2012/10/7 Michael Segel <michael_segel@hotmail.com>
>> Rack local means that while the data isn't local to the node running the
>> task, it is still on the same rack.
>> (Its meaningless unless you've set up rack awareness because all of the
>> machines are on the default rack. )
>> Data local means that the task is running local to the machine that
>> contains the actual data.
>> HTH
>> -Mike
>> On Oct 7, 2012, at 8:56 AM, centerqi hu <centerqi@gmail.com> wrote:
>> hi all
>> When I run "hadoop job -status xxx",Output the following some list.
>> Rack-local map tasks=124
>> Data-local map tasks=6
>> What is the difference between Rack-local map tasks and Data-local map
>> tasks?
>> --
>> centerqi@gmail.com|Sam
> --
> centerqi@gmail.com|齐忠

Bertrand Dechoux

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