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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 Tue, 20 Jun 2017 16:57:00 GMT

    [ https://issues.apache.org/jira/browse/DERBY-6940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16056079#comment-16056079
] 

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

Another thing, I am able to write and read the minVal and maxVal as strings successfully using
their toString methods, but when trying to store the original DataValueDescriptor object,
I get the following error while trying to read the statistics -

ERROR XSDA8: Exception during restore of a serializable or SQLData object of cla
ss
ERROR XJ001: Java exception: 'java.lang.ClassCastException: java.lang.String can
not be cast to org.apache.derby.iapi.types.DataValueDescriptor: java.io.StreamCo
rruptedException'.
ERROR XJ001: Java exception: 'java.lang.String cannot be cast to org.apache.derb
y.iapi.types.DataValueDescriptor: java.lang.ClassCastException'. 

Storing minVal and maxVal using String is not preferred for comparisons later on, I am trying
to store the original object.

> 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_2.diff, 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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