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From Lance Norskog <goks...@gmail.com>
Subject Re: Predicting how many values will I see in a call to reduce?
Date Tue, 09 Nov 2010 07:40:47 GMT
It is key to the scheduling paradigm of Hadoop that it doesn't have to
tell you how many or when. It would have to store up all of the data
for your key before activating your reducer. This is exactly what it
cannot do and scale.


On Mon, Nov 8, 2010 at 3:32 AM, Niels Basjes <Niels@basjes.nl> wrote:
> Hi,
> 2010/11/7 Anthony Urso <anthony.urso@gmail.com>
>> Is there any way to know how many values I will see in a call to
>> reduce without first counting through them all with the iterator?
>> Under 0.21? 0.20? 0.19?
> I've looked for an answer to the same question a while ago and came to the
> conclusion that you can't.
> The main limit is that the Iterator does not have a "size" or "length"
> method.
> --
> Met vriendelijke groeten,
> Niels Basjes

Lance Norskog

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