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From "Swati Jain (JIRA)" <j...@apache.org>
Subject [jira] Created: (PIG-1494) PIG Logical Optimization: Use CNF in PushUpFilter
Date Mon, 12 Jul 2010 17:10:01 GMT
PIG Logical Optimization: Use CNF in PushUpFilter
-------------------------------------------------

                 Key: PIG-1494
                 URL: https://issues.apache.org/jira/browse/PIG-1494
             Project: Pig
          Issue Type: Improvement
          Components: impl
    Affects Versions: 0.7.0
            Reporter: Swati Jain
            Priority: Minor
             Fix For: 0.8.0


The PushUpFilter rule is not able to handle complicated boolean expressions.

For example, SplitFilter rule is splitting one LOFilter into two by "AND". However it will
not be able to split LOFilter if the top level operator is "OR". For example:

*ex script:*
A = load 'file_a' USING PigStorage(',') as (a1:int,a2:int,a3:int);
B = load 'file_b' USING PigStorage(',') as (b1:int,b2:int,b3:int);
C = load 'file_c' USING PigStorage(',') as (c1:int,c2:int,c3:int);
J1 = JOIN B by b1, C by c1;
J2 = JOIN J1 by $0, A by a1;
D = *Filter J2 by ( (c1 < 10) AND (a3+b3 > 10) ) OR (c2 == 5);*
explain D;
In the above example, the PushUpFilter is not able to push any filter condition across any
join as it contains columns from all branches (inputs). But if we convert this expression
into "Conjunctive Normal Form" (CNF) then we would be able to push filter condition c1<
10 and c2 == 5 below both join conditions. Here is the CNF expression for highlighted line:

( (c1 < 10) OR (c2 == 5) ) AND ( (a3+b3 > 10) OR (c2 ==5) )

*Suggestion:* It would be a good idea to convert LOFilter's boolean expression into CNF, it
would then be easy to push parts (conjuncts) of the LOFilter boolean expression selectively.
We would also not require rule SplitFilter anymore if we were to add this utility to rule
PushUpFilter itself.

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