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Posted to issues@trafodion.apache.org by "Alice Chen (JIRA)" <ji...@apache.org> on 2015/07/22 20:14:08 UTC

[jira] [Created] (TRAFODION-58) LP Blueprint: estimate-rowcount - Estimate table row count when histograms not available

Alice Chen created TRAFODION-58:
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             Summary: LP Blueprint: estimate-rowcount - Estimate table row count when histograms not available
                 Key: TRAFODION-58
                 URL: https://issues.apache.org/jira/browse/TRAFODION-58
             Project: Apache Trafodion
          Issue Type: New Feature
            Reporter: Barry Fritchman
            Assignee: Barry Fritchman


The default table cardinality estimate of 100 often leads to poor query plans. A better alternative is needed in cases where stats are not available for a given table. A reasonable estimate can be derived from the KeyValue entry count stored in the trailer block of each HFile. This approach has recently been used in Update Stats, and this mini-project will make use of it in the Optimizer.  Additional details are available in the commit message at https://review.trafodion.org/#/c/422/.



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