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From "Mike Matrigali (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-269) Provide some way to update index cardinality statistics (e.g. reimplement update statistics)
Date Fri, 25 Jul 2008 20:47:31 GMT

     [ https://issues.apache.org/jira/browse/DERBY-269?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Mike Matrigali updated DERBY-269:
---------------------------------


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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