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From "Santhosh Srinivasan (JIRA)" <j...@apache.org>
Subject [jira] Created: (PIG-873) Optimizer should allow search for global patterns
Date Tue, 07 Jul 2009 21:42:14 GMT
Optimizer should allow search for global patterns
-------------------------------------------------

                 Key: PIG-873
                 URL: https://issues.apache.org/jira/browse/PIG-873
             Project: Pig
          Issue Type: Improvement
    Affects Versions: 0.3.1
            Reporter: Santhosh Srinivasan
             Fix For: 0.4.0


Currently, the optimizer works on the following mechanism:

1. Specify the pattern to be searched
2. For each occurrence of the pattern, check and then apply a transformation

With this approach, the search for a pattern is localized. An example will illustrate the
problem.

If the pattern to be searched for is foreach (with flatten) connected to any operator and
if the graph has more than one foreach (with flatten) connected to an operator (cross, join,
union, etc), then each instance of foreach connected to the operator is returned as a match.
While this is fine for a localized view (per match), at a global view the pattern to be searched
for is any number of foreach connected to an operator.

The implication of not having a globalized view is more rules. There will be one rule for
one foreach connected to an opeator, one rule for two foreachs connected to an operators,
etc.


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