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https://issues.apache.org/jira/browse/PIG-2747?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13292983#comment-13292983
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Daniel Dai commented on PIG-2747:
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My understanding is there is a union after T1, T2, right?
Yes we only merge the consecutive filter into "and" condition. We don't merge
"or" condition. So you want
filter cond1, filter cond2 -> union ==> filter cond1 or cond2
> 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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