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https://issues.apache.org/jira/browse/PIG-4940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15353741#comment-15353741
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Cheolsoo Park commented on PIG-4940:
------------------------------------
Sorry, but I'll let someone who is still active in the community review your
patch...
> Predicate push-down filtering unary expressions can be pushed.
> --------------------------------------------------------------
>
> Key: PIG-4940
> URL: https://issues.apache.org/jira/browse/PIG-4940
> Project: Pig
> Issue Type: Bug
> Reporter: Ryan Blue
>
> While testing predicate push-down, I ran into the following error:
> {code:title=Pig Exception}
> ERROR 0: Unsupported conversion of LogicalExpression to Expression: Map
> at
> org.apache.pig.newplan.FilterExtractor.getExpression(FilterExtractor.java:389)
> at
> org.apache.pig.newplan.FilterExtractor.getExpression(FilterExtractor.java:401)
> at
> org.apache.pig.newplan.FilterExtractor.getExpression(FilterExtractor.java:378)
> at
> org.apache.pig.newplan.FilterExtractor.getExpression(FilterExtractor.java:401)
> at
> org.apache.pig.newplan.FilterExtractor.getExpression(FilterExtractor.java:380)
> at
> org.apache.pig.newplan.FilterExtractor.visit(FilterExtractor.java:109)
> at
> org.apache.pig.newplan.PredicatePushDownFilterExtractor.visit(PredicatePushDownFilterExtractor.java:70)
> at
> org.apache.pig.newplan.logical.rules.PredicatePushdownOptimizer$PredicatePushDownTransformer.transform(PredicatePushdownOptimizer.java:146)
> at
> org.apache.pig.newplan.optimizer.PlanOptimizer.optimize(PlanOptimizer.java:110)
> ... 19 more
> {code}
> The problem is that the code is trying to push a map access operation, that
> isn't supported. The cause appears to be the logic in
> {{checkPushDown(UnaryExpression)}} that separates expressions that can be
> pushed from expressions that must be run by Pig. This function assumes that
> any expression under {{IsNullExpression}} or {{NotExpression}} can be pushed
> and adds the unary node's child expression to the pushdown expression without
> calling {{checkPushDown}} on it.
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