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From novice user <pallavip...@gmail.com>
Subject Re: Combiner is optional though it is specified?
Date Thu, 03 Jul 2008 08:52:01 GMT

To my surprise, only one output value of mapper is not reaching combiner. and
It is consistent when I repeated the experimentation. Same point directly
reaches reducer without going thru the combiner. I am surprised how can this
happen?



novice user wrote:
> 
> Regarding the conclusion,
>  I am  parsing the inputs in combiner and reducer differently. For example
> the output value of mapper is "s:d" where as the output value of combiner
> is "s,d". So, in reducer, I am assuming the input as "s,d" and trying to
> parse it. There I got the exception because it got input as "s:d".
> 
> I am using hadoop-17. 
> 
> Icouldn't get  exactly what you meant by no guarantee on the number of
> times a combiner is run. Can you please elaborate a bit on this?
> 
> Thanks
> 
> 
> 
> 
> 
> 
> Arun C Murthy-2 wrote:
>> 
>> 
>> On Jul 1, 2008, at 4:04 AM, novice user wrote:
>> 
>>>
>>> Hi all,
>>>    I have a query regarding the functionality of combiner.
>>> Is it possible to ignore combiner code for some of the outputs of  
>>> mapper and
>>> directly being sent to reducer though combiner is specified in job
>>> configuration?
>>> Because, I figured out that, when I am running on large amounts of  
>>> data,
>>> some of the mapper output is directly reached reducer. I am  
>>> wondering how
>>> can this be possible when I have specified combiner in the job
>>> configuration. Can any one please  let me know if this thing happens?
>>>
>> 
>> Can you elaborate on how you reached the conclusion that the output  
>> of some maps isn't going through the combiner?
>> 
>> Also, what version of hadoop are you using? hadoop-0.18 onwards there  
>> aren't guarantees on the number of times a combiner is run...
>> 
>> Arun
>> 
>>>
>>>
>>> -- 
>>> View this message in context: http://www.nabble.com/Combiner-is- 
>>> optional-though-it-is-specified--tp18213887p18213887.html
>>> Sent from the Hadoop core-user mailing list archive at Nabble.com.
>>>
>> 
>> 
>> 
> 
> 

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