org.apache.hadoop.hive.ql.optimizer.unionproc
Class UnionProcessor
java.lang.Object
org.apache.hadoop.hive.ql.optimizer.unionproc.UnionProcessor
- All Implemented Interfaces:
- Transform
public class UnionProcessor
- extends Object
- implements Transform
Implementation of the union processor. This can be enhanced later on.
Currently, it does the following: Identify if both the subqueries of UNION
are map-only. Store that fact in the unionDesc/UnionOperator. If either of
the sub-query involves a map-reduce job, a FS is introduced on top of the
UNION. This can be later optimized to clone all the operators above the
UNION.
The parse Context is not changed.
UnionProcessor
public UnionProcessor()
- empty constructor.
transform
public ParseContext transform(ParseContext pCtx)
throws SemanticException
- Transform the query tree. For each union, store the fact whether both the
sub-queries are map-only
- Specified by:
transform
in interface Transform
- Parameters:
pCtx
- the current parse context
- Returns:
- ParseContext
- Throws:
SemanticException
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