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


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Effyroth Gu 2013-04-09, 14:35
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Re: How can I record some position of context in Reduce()?
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.
>>>>
>>>> Any help will be appreciated.
>>>>
>>>>
>>>> 2013/3/13 Roth Effy <[EMAIL PROTECTED]>
>>>>> I want a n:n join as Cartesian product,but the DataJoinReducerBase looks like only support equal join.
>>>>> I want a non-equal join,but I have no idea now.
>>>>>
>>>>>
>>>>> 2013/3/13 Azuryy Yu <[EMAIL PROTECTED]>
>>>>>> you want a n:n join or 1:n join?
>>>>>>
>>>>>> On Mar 13, 2013 10:51 AM, "Roth Effy" <[EMAIL PROTECTED]> wrote:
>>>>>>> I want to join two table data in reducer.So I need to find the start of the table.
>>>>>>> someone said the DataJoinReducerBase can help me,isn't it?
>>>>>>>
>>>>>>>
>>>>>>> 2013/3/13 Azuryy Yu <[EMAIL PROTECTED]>
>>>>>>>> you cannot use RecordReader in Reducer.
>>>>>>>>  
>>>>>>>> what's the mean of you want get the record position? I cannot understand, can you give a simple example?
>>>>>>>>
>>>>>>>>
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Vikas Jadhav 2013-04-10, 13:11
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Michel Segel 2013-04-10, 16:05
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Vikas Jadhav 2013-04-11, 04:18
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Michel Segel 2013-04-12, 12:51
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB