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https://issues.apache.org/jira/browse/DERBY-269?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mike Matrigali updated DERBY-269:
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i agree now that the selectivity maintains the "number of unique values" and
then uses this along with the "number of rows" to export a selectivity
percentage.
As to the short circuit discussion, I just don't know if the optimizer will
actually ever ask for the selectivity of something
that it knows is unique - i actually hope not. Note that the actual row count
is only available with a full scan, the one
maintained by store is only an estimate. But in this case it may just be good
enough to store the estimate row count as
both the row count and the number of rows.
> Provide some way to update index cardinality statistics (e.g. reimplement
> update statistics)
> --------------------------------------------------------------------------------------------
>
> Key: DERBY-269
> URL: https://issues.apache.org/jira/browse/DERBY-269
> Project: Derby
> Issue Type: New Feature
> Components: SQL
> Affects Versions: 10.0.2.0, 10.0.2.1, 10.1.1.0, 10.2.2.0, 10.3.1.4
> Reporter: Stan Bradbury
> Assignee: Mamta A. Satoor
> Fix For: 10.5.0.0
>
> Attachments: DERBY269_update_statistics_svndiff_ver1.txt,
> DERBY269_update_statistics_svndiff_ver2.txt,
> DERBY269_update_statistics_svnstat_ver1.txt,
> DERBY269_update_statistics_svnstat_ver2.txt
>
>
> Performance problems are being reported that can be resolved by updating the
> cardinality statistics used by the optimizer. Currently the only time the
> statistics are guaranteed to be an up-to-date is when the index is first
> created on a fully populated table. This is most easily accomplished on an
> existing table by using the command:
> alter table <table-name> compress [sequential]
> Compress table is an I/O intensive task. A better way to achieve this would
> be to re-enable parser support for the 'update statistics' command or
> re-implement the update in some other fashion.
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