Chao Sun created HIVE-15477:
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Summary: Provide options to adjust filter stats when column stats
are not available
Key: HIVE-15477
URL: https://issues.apache.org/jira/browse/HIVE-15477
Project: Hive
Issue Type: Bug
Components: Statistics
Affects Versions: 2.2.0
Reporter: Chao Sun
Assignee: Chao Sun
Currently when column stats are not available, Hive will assume the "worst"
case by setting the # of output rows to be 1/2 of the # of input rows, for each
predicate expression. This could be inaccurate, especially in the presence of
multiple predicates chained by AND. We have found in some cases this could
cause map join to have wrong ordering and thus fail with memory issue.
One suggestion is to provide a config (such as {{hive.stats.filter.factor}})
that can be used to control the percentage of rows emitted by a predicate
expression.
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