[jira] [Commented] (TRAFODION-2282) Optimizer histogram cache is sometimes never refreshed

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

    [ https://issues.apache.org/jira/browse/TRAFODION-2282?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15572489#comment-15572489 ] 

David Wayne Birdsall commented on TRAFODION-2282:
-------------------------------------------------

See JIRA TRAFODION-882 for a related problem.

> Optimizer histogram cache is sometimes never refreshed
> ------------------------------------------------------
>
>                 Key: TRAFODION-2282
>                 URL: https://issues.apache.org/jira/browse/TRAFODION-2282
>             Project: Apache Trafodion
>          Issue Type: Bug
>          Components: sql-cmp
>    Affects Versions: 2.1-incubating
>         Environment: All
>            Reporter: David Wayne Birdsall
>            Assignee: David Wayne Birdsall
>             Fix For: 2.1-incubating
>
>
> Here's the scenario:
> In session 1, create a table T1 and populate it with, say, 200000 or more rows.
> In session 2, prepare a query that selects from T1. For example, select A,COUNT(*) FROM T1 GROUP BY A. The query should compile fine, but you should see missing statistics warning messages (warning codes 6007 and 6008).
> In session 1, do "update statistics for table t1 on every column"
> In session 2, prepare other queries over a period of time. What should happen is that after about an hour, the Optimizer decides to refresh the histograms. However, due to a bug, it might never do so. So, the missing statistics warnings (6007, 6008) never go away. Worse, the prepares never benefit from the statistics so plan choice may be poor.



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