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From: Apache Wiki <wikidiffs@apache.org>
To: pig-commits@incubator.apache.org
Date: Tue, 22 Jan 2008 07:26:35 -0000
Message-ID: <20080122072635.22031.94196@eos.apache.org>
Subject: [Pig Wiki] Update of "PigExecutionModel" by UtkarshSrivastava

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

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  Each of the above logical operators will translate to a physical operator (in many cases, the physical operator will be shared between backends, as shown in the above table).
  
  One physical operators have been linked together into a query plan, they must be executed. There is a choice of mainly 2 models for execution (assume that data flows downwards in an execution plan):
+ 
+ attachment:simple.png
  
   1. '''Push''': Operator A pushes data to B that operates on it, and pushes the result  to C.
   2. '''Pull''': Operator C asks B for its next data item. If B has nothing pending to return, it asks A. When A returns a data item, B operates on it, and finally returns the result to C.