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https://issues.apache.org/jira/browse/TRAFODION-3158?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16554534#comment-16554534
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ASF GitHub Bot commented on TRAFODION-3158:
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Github user asfgit closed the pull request at:
https://github.com/apache/trafodion/pull/1660
> Bad histogram values are sometimes not reported
> -----------------------------------------------
>
> Key: TRAFODION-3158
> URL: https://issues.apache.org/jira/browse/TRAFODION-3158
> Project: Apache Trafodion
> Issue Type: Bug
> Components: sql-cmp
> Affects Versions: 2.3
> Reporter: David Wayne Birdsall
> Assignee: David Wayne Birdsall
> Priority: Major
>
> Function EncodedValue::constructorFunction has logic to raise a 6003 warning
> if it encounters invalid values in histogram intervals. When this happens,
> the compiler generates a default histogram for that column (that is, it
> behaves as if it has no statistics for that column.) This can lead to poor
> query plans. In some circumstances, however, this warning does not get
> reported, so the user is not aware of the possible compromise in plan quality.
> An example of this can be created as follows:
> # Create a Hive table Test1 with columns (a int, b int). Put some data into
> it, and in Trafodion, use UPDATE STATISTICS FOR TABLE HIVE.HIVE.TEST1 to
> generate statistics for it.
> # Outside of Trafodion (in the Hive shell, say), drop and recreate the Hive
> table, but this time with columns (a string, b string). Populate that with a
> few rows.
> # In a fresh sqlci session, do "prepare s1 from select a,b from
> hive.hive.test1 where a < 'abcd';". This will appear to be successful,
> however in fact 6003 warnings were generated internally but not reported.
> Another way to create an example is to create a Trafodion table, test1, with
> columns (a char(4), b char(4). Put some rows into it and do UPDATE STATISTICS
> on it. Then manually alter the boundary value in one of the
> SB_HISTOGRAM_INTERVALS tables, changing a value from a character string
> literal to a numeric literal. For example, change "('abcd')" to "(3)".
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