Jesus Camacho Rodriguez created HIVE-8625:
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Summary: Some union queries result in plans with many unions with
CBO on
Key: HIVE-8625
URL: https://issues.apache.org/jira/browse/HIVE-8625
Project: Hive
Issue Type: Bug
Components: CBO
Affects Versions: 0.14.0, 0.15.0
Reporter: Jesus Camacho Rodriguez
Priority: Minor
For some queries e.g. union9, union16, we are getting plans with many binary
unions when CBO is on. The reason is that an identity select operator is
introduced after each union by the CBO; thus, the method that was merging the
unions when the translation of the AST into a logical plan was being done is
not executed, as it does not detect there is another union operator.
With the fix in the patch attached, the method will merge the two unions if (1)
one is the child of the other one, or (2) if one is a descendant of the other
one and there is an identity select operator between them.
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