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The following page has been changed by Shravan Narayanamurthy:
http://wiki.apache.org/pig/PigExecutionModel

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  The logical operator co-group would be converted to 3 physical operators the 
Local Rearrange, Global Rearrange and Package as shown below:
  
- attachment:Group.jpg
+ attachment:Group.png
  
  There will be a Local Rearrange operator for each input which will aggregate 
to a Global Rearrange followed by a Package as shown below:
  
- attachment:GroupPhy.jpg
+ attachment:GroupPhy.png
  
  The Local Rearrange takes the input tuple and outputs a key, value pair with 
the group field as the key and the tuple as the value. For eg., (1,R) will be 
converted to {1,(1,R)}. Also the tuple is tagged with the input index it 
originated from. In our case, if (1,R) came from A it would be tagged 1 and if 
it was from B it would be tagged 2. 
  

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