Yu Xu created PIG-2747:
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Summary: Support more predicate pushdown to a data source by
pulling up multiple predicates from branches using the same data source
Key: PIG-2747
URL: https://issues.apache.org/jira/browse/PIG-2747
Project: Pig
Issue Type: Improvement
Reporter: Yu Xu
Priority: Minor
consider the following example:
T = load ... ;
T1 = filter T by col == 'hello';
T2 = filter T by col =='world';
currently Pig optimizer does not combine the two predicates and cannot push
down the predicates to the data sources (via LoadMetadata). Thus the data
source cannot do any filtering. A full table/file scan is required.
A current more efficient workaround (by hand) is to rewrite the above script to
the following equivalent one:
T = load ...;
T = filter T by col == 'hello' or col == 'world' ;
T1 = filter T by col == 'hello';
T2 = filter T by col == 'world';
the above script enables Pig to push down the predicate (col == 'hello' or col
== 'world') to the data source to use available partitions/indexes for
potentially much more efficient processing.
This JIRA is created to request PIG optimizer to perform the above type of
optimization automatically.
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