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

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  attachment:FILTERTranslation.png
  
+ === Comments ===
+ 
+ The Physical plan and the Logical Plan were not clear to me probably because 
of the nested query plan thingy. I think we need to find a better way to draw 
this because, the conditional expression is an attribute of the filter and not 
an input to filter.
+ 
+ 
  __GROUP__
  
  The logical operator co-group would be converted to 3 physical operators the 
Local Rearrange, Global Rearrange and Package as shown below:
@@ -177, +182 @@

  
  The Package just takes each key, list of values and puts it in appropriate 
format as required by the co-group. So lets say we have (1,R),(2,G) in A and 
(1,B), (2,Y) in B. If there are two reducers, Global Rearrange catering to 
reducer 1 will have {1,{(1,R),(1,B)}} as the key, list of values which should 
be converted into an output tuple for co-group based on the tagged index of the 
tuples in the list. So this would be converted to {1,{(1,R)},{(1,B)}}. 
Similarly, {2,{(2,G),(2,Y)}} will be converted to {2,{(2,G)},{(2,Y)}} by 
reducer 2.
  
- === Comments ===
- 
- The Physical plan and the Logical Plan were not clear to me probably because 
of the nested query plan thingy. I think we need to find a better way to draw 
this because, the conditional expression is an attribute of the filter and not 
an input to filter.
- 

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