[jira] [Commented] (DERBY-4113) Make new optimizer directive for USESTATISTICS=

["Myrna van Lunteren (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DERBY-4113?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14178461#comment-14178461 ] 

Myrna van Lunteren commented on DERBY-4113:
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For Derby 6305 I did a little research and it appears this functionality is actually working, to repeat:

According to a comment in Optimizer.java, useStatistics can be used in a query and is a 'Property name for disabling statistics use for all queries.' It matches the derby.optimizer.useStatistics property.
I believe this is a left-over from the Cloudscape-style optimizer properties. I think these are index, or cardinality, statistics, not runtime statistics.

The property is used once in the tests in SelectivityTest.java was converted from an old cloudscape test after optimizer overrides/directives were supported in Derby. In that test it gives the same results with useStatistics=false or true or without. But the value of the estimated rowcount is different with useStatistics=false, so this override is working.

However, further work is needed;
- document this optimizer override
- test/verify the correct error comes up when an incorrect value is entered
- test/verify/analyze the need for the matching property derby.optimizer.usestatistics
  - if desired/working, document this derby property.

> Make new optimizer directive for USESTATISTICS=<true|false>
> -----------------------------------------------------------
>
>                 Key: DERBY-4113
>                 URL: https://issues.apache.org/jira/browse/DERBY-4113
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 10.6.1.0
>            Reporter: Kathey Marsden
>            Priority: Minor
>              Labels: derby_triage10_10
>
> Now that we have a way to update statistics, more people will be using them.  It would be nice to have an optimizer directive --DERBY-PROPERTIES USESTATISTICS=<true|false>



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