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https://issues.apache.org/jira/browse/DERBY-6940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16063622#comment-16063622
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Harshvardhan Gupta commented on DERBY-6940:
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Since I am performing deep copy of the objects, I don't think (min==max) will
work in our case. So I had to use the equality function that is implemented by
each data type, the problem is that I need to catch the StandardException
thrown by those functions and I can't delegate it to the writeExternal method
since the interface definition won't let it compile.
I too believe that the code in present form is little clunky and open for
potential improvements.
> 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_3.diff, derby-6940.diff,
> EOFException_derby.log, EOFException.txt
>
>
> 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.
> We eventually want to utilize the new statistics to make better selectivity
> estimates / cost estimates that will help find the best query plan. Currently
> Derby keeps two type of stats - the total row count and the number of unique
> values.
> We are initially extending the stats to include null count, the minimum value
> and maximum value associated with each of the columns of an index. This would
> be useful in selectivity estimates for operators such as [ IS NULL, <, <=, >,
> >= ] , all of which currently rely on hardwired selectivity estimates.
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