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