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From Sai Sai <saigr...@yahoo.in>
Subject Re: 100K Maps scenario
Date Sat, 13 Apr 2013 01:45:28 GMT


Just a follow up to see if anyone can shed some light on this:
My understanding is that each block after getting replicated 3 times, a map task is run on
each of the replica in parallel.
The thing i am trying to double verify is in a scenario where a file is split into 10K or
100K or more blocks it will result in atleast 300K Map tasks being performed and this looks
like an overkill from a performance or just a logical perspective. 
Will appreciate any thoughts on this.
Thanks
Sai

________________________________
 From: Sai Sai <saigraph@yahoo.in>
To: "user@hadoop.apache.org" <user@hadoop.apache.org>; Sai Sai <saigraph@yahoo.in>

Sent: Friday, 12 April 2013 1:37 PM
Subject: Re: Does a Map task run 3 times on 3 TTs or just once
 


Just wondering if it is right to assume that a Map task is run 3 times on 3 different TTs
in parallel and whoever completes processing the task first that output is picked up and written
to intermediate location.
Or is it true that a map task even though its data is replicated 3 times will run only once
and other 2 will be on the stand by just incase this fails the second one will run followed
by 3rd one if the 2nd Mapper fails.
Plesae pour some light.
Thanks
Sai
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