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Accumulo >> mail # user >> upgrade from 1.3 to 1.4


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Re: upgrade from 1.3 to 1.4
Ahh that's awesome. So the function returns exactly one value for each key?

On Jan 3, 2012, at 12:53 PM, Billie J Rinaldi wrote:

> On Tuesday, January 3, 2012 11:56:50 AM, "Aaron Cordova" <[EMAIL PROTECTED]> wrote:
>> BTW I love the label 'Combiner' instead of aggregator. I've been
>> describing their capabilities as equivalent to MapReduce combiners to
>> new Accumulo users, so this makes it even more clear.
>>
>> Are they easier to code up too? It'd be sweet if one could basically
>> just define a function such as
>>
>> public void combine(Key k, Iterator<Value> v)
>>
>> or some such simple signature
>
> That's basically it.  Here's the method you implement:
> public Value reduce(Key k, Iterator<Value> v);
>
> We've also done something exciting with the TypedValueCombiner<V>.  It uses an Encoder<V> which has decode and encode methods to translate from a Value's byte array to type V and back.  Then you implement this method to do the combining:
> public V typedReduce(Key k, Iterator<V> v);
>
> We provide a LongCombiner which is a TypedValueCombiner<Long> with three built-in encoding types: STRING, VARLEN, and FIXEDLEN.  Separating the encoding from the combining has made writing new combiners really easy.  See the MaxCombiner and MinCombiner in addition to the SummingCombiner.
>
> Billie