[jira] [Created] (TRAFODION-3158) Bad histogram values are sometimes not reported

["David Wayne Birdsall (JIRA)" <ji...@apache.org>]

David Wayne Birdsall created TRAFODION-3158:
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             Summary: 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


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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