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Hadoop, mail # user - guessing number of reducers.


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guessing number of reducers.
jamal sasha 2012-11-21, 16:38
By default the number of reducers is set to 1..
Is there a good way to guess optimal number of reducers....
Or let's say i have tbs worth of data... mappers are of order 5000 or so...
But ultimately i am calculating , let's say, some average of whole data...
say average transaction occurring...
Now the output will be just one line in one "part"... rest of them will be
empty.So i am guessing i need loads of reducers but then most of them will
be empty but at the same time one reducer won't suffice..
What's the best way to solve this..
How to guess optimal number of reducers..
Thanks