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MapReduce >> mail # user >> Re: How can I record some position of context in Reduce()?


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Re: How can I record some position of context in Reduce()?
Not sure what is meant by a non equi join.

Are you saying something like for every row in X, join it to all of the rows in Y where Y.a < something?

Is that what you are suggesting?
Sent from a remote device. Please excuse any typos...

Mike Segel

On Apr 10, 2013, at 9:11 AM, Vikas Jadhav <[EMAIL PROTECTED]> wrote:

> How are you going to support NON EQUI Join using MapReduce ?
> As per my understanding there is only one way to do this is
> to bring all data to one reducer then reducer will know lesser/greater
> values correctly.
> Correct me if I am wrong.
> Thank You.
>  
>   Regards,
>   Vikas
>  
>
>
> On Wed, Apr 10, 2013 at 4:22 PM, Michel Segel <[EMAIL PROTECTED]> wrote:
>> Can you show an example of your join?
>> All joins are an equality in that the key has to match.
>> Whether its a one to one , one to many, or many to many remains to be seen.
>>
>>
>> Sent from a remote device. Please excuse any typos...
>>
>> Mike Segel
>>
>> On Apr 9, 2013, at 10:35 AM, Effyroth Gu <[EMAIL PROTECTED]> wrote:
>>
>>> Only equality joins, outer joins, and left semi joins are supported in Hive. Hive does not support join conditions that are not equality conditions as it is very difficult to express such conditions as a map/reduce job. Also, more than two tables can be joined in Hive.
>>>
>>>
>>> 2013/4/9 Michael Segel <[EMAIL PROTECTED]>
>>>> Hi,
>>>>
>>>> Your cross join is supported in both pig and hive. (Cross, and Theta joins)
>>>>
>>>> So there must be code to do this.
>>>>
>>>> Essentially in the reducer you would have your key and then the set of rows that match the key. You would then perform the cross product on the key's result set and output them to the collector as separate rows.
>>>>
>>>> I'm not sure why you would need the reduce context.
>>>>
>>>> But then again, I'm still on my first cup of coffee. ;-)
>>>>
>>>>
>>>> On Apr 9, 2013, at 12:15 AM, Vikas Jadhav <[EMAIL PROTECTED]> wrote:
>>>>
>>>>> Hi
>>>>> I am also woring on join using MapReduce
>>>>> i think instead of finding postion of table in RawKeyValuIterator.
>>>>> what we can do modify context.write method to alway write key as table name or id
>>>>> then we dont need to find postion we can get Key and Value from "reducerContext"
>>>>>  
>>>>> befor calling reducer.run(reducerContext) in ReduceTask.java we can  add
>>>>> method join in Reducer.java Reducer class and give call to reducer.join(reduceContext)
>>>>>  
>>>>>  
>>>>> I just wonder how r going to support NON EQUI join.
>>>>>  
>>>>> I am also having same problem how to do join if datasets cant fit in to memory.
>>>>>  
>>>>>  
>>>>> for now i am cloning using following code :
>>>>>  
>>>>>  
>>>>> KEYIN key = context.getCurrentKey() ;
>>>>> KEYIN outKey = null;
>>>>> try {
>>>>>     outKey = (KEYIN)key.getClass().newInstance();
>>>>>    }
>>>>> catch(Exception e)
>>>>>  {}        
>>>>> ReflectionUtils.copy(context.getConfiguration(), key, outKey);      
>>>>>
>>>>>  Iterable<VALUEIN> values = context.getValues();
>>>>>  ArrayList<VALUEIN> myValues = new ArrayList<VALUEIN>();
>>>>>  for(VALUEIN value: values) {        
>>>>>    VALUEIN outValue = null;
>>>>>     try {
>>>>>          outValue = (VALUEIN)value.getClass().newInstance();
>>>>>    }
>>>>>    catch(Exception e)    {}          
>>>>>    ReflectionUtils.copy(context.getConfiguration(), value, outValue);
>>>>>  }
>>>>>  
>>>>>  
>>>>> if you have found any other solution please feel free to share
>>>>>  
>>>>> Thank You.
>>>>>  
>>>>>        
>>>>>  
>>>>>  
>>>>>
>>>>>
>>>>> On Thu, Mar 14, 2013 at 1:53 PM, Roth Effy <[EMAIL PROTECTED]> wrote:
>>>>>> In reduce() we have:
>>>>>>
>>>>>> key1 values1
>>>>>> key2 values2
>>>>>> ...
>>>>>> keyn valuesn
>>>>>>
>>>>>> so,what i want to do is join all values like a SQL:
>>>>>>
>>>>>> select * from values1,values2...valuesn;
>>>>>>
>>>>>> if memory is not enough to cache values,how to complete the join operation?
>>>>>> my idea is clone the reducecontext,but it maybe not easy.