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https://issues.apache.org/jira/browse/DERBY-6305?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14177893#comment-14177893
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Myrna van Lunteren edited comment on DERBY-6305 at 10/21/14 4:05 AM:
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According to a comment in Optimizer.java, useStatistics is a 'Property name for
disabling statistics use for all queries.'
I believe this is a left-over from the Cloudscape-style optimizer properties. I
think these are index, or cardinality, statistics, not runtime statistics.
There is an open enhancement suggesting to revive this - DERBY-4113.
The property is used once in the tests in SelectivityTest.java was converted
from an old cloudscape test. In that example it gives the same results with
useStatistics=false or true or without, so either it's not a useful test or
it's not working.
was (Author: myrna):
According to a comment in Optimizer.java, useStatistics is a 'Property name for
disabling statistics use for all queries.'
I believe this is a left-over from the Cloudscape-style optimizer properties. I
think these are index, or cardinality, statistics, not runtime statistics.
There is an open enhancement suggesting to revive this - DERBY-4113.
I do not know if this property currently does anything.
> Tuning Derby information on optimizer overrides needs improvement
> -----------------------------------------------------------------
>
> Key: DERBY-6305
> URL: https://issues.apache.org/jira/browse/DERBY-6305
> Project: Derby
> Issue Type: Bug
> Components: Documentation
> Affects Versions: 10.10.1.1
> Reporter: Kim Haase
> Attachments: DERBY-6305.diff, DerbyDashProperties.html,
> ctundepthoptover.html
>
>
> The topic "Optimizer overrides" in the Tuning Derby manual talks about using
> the "-- DERBY-PROPERTIES" clause to specify overrides but doesn't include a
> link to the topic later in the manual, "Overriding the default optimizer
> behavior", that explains how to use the clause. This undoubtedly results in
> user confusion.
> The first topic is
> http://db.apache.org/derby/docs/10.10/tuning/ctundepthoptover.html; the
> second is
> http://db.apache.org/derby/docs/10.10/tuning/ctunoptimzoverride.html.
> I'll add the link, and I welcome additional suggestions on how to improve
> these topics.
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