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From "Harshvardhan Gupta (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-6940) Enhance derby statistics for more accurate selectivity estimates.
Date Sun, 18 Jun 2017 13:53:00 GMT

    [ https://issues.apache.org/jira/browse/DERBY-6940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16053201#comment-16053201
] 

Harshvardhan Gupta commented on DERBY-6940:
-------------------------------------------

Additionally we need to work on upgrade procedures, while trying to access statistics info
of an index created before this patch, Derby will throw a NPE due to absence of the new statistics.


> Enhance derby statistics for more accurate selectivity estimates.
> -----------------------------------------------------------------
>
>                 Key: DERBY-6940
>                 URL: https://issues.apache.org/jira/browse/DERBY-6940
>             Project: Derby
>          Issue Type: Sub-task
>          Components: SQL
>            Reporter: Harshvardhan Gupta
>            Assignee: Harshvardhan Gupta
>            Priority: Minor
>         Attachments: derby-6940.diff
>
>
> Derby should collect extra statistics during index build time, statistics refresh time
which will help optimizer make more precise selectivity estimates and chose better execution
paths.



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