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From "Myrna van Lunteren (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (DERBY-6305) Tuning Derby information on optimizer overrides needs improvement
Date Tue, 21 Oct 2014 04:11:33 GMT

    [ 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 4:11 AM:
---------------------------------------------------------------------

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.
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 after optimizer overrides/directives were supported in Derby. In that test 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.

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.



> 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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