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https://issues.apache.org/jira/browse/DERBY-269?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12548115
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Matt Doran commented on DERBY-269:
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I agree that it would be great to have a way to update stats without a full
compress/rebuild (which is pretty IO intensive). We user a derby in a
commercial application, and we found some extremely poor performance if the
stats were not up-to-date. Updating the stats made the problem query run in
less than 1 second (it previously took 22 minutes!)
See here for the details:
http://thread.gmane.org/gmane.comp.apache.db.derby.user/8098 and here for the
resolution:
http://thread.gmane.org/gmane.comp.apache.db.derby.user/8100/focus=8103
It would be great if derby could update the statistics itself. It would
probably result in a much better out-of-the-box performance for most users.
For now we've implemented a maintenance task in our application that
periodically performs the compress operation.
Maybe an interim step to make the documentation very clear that you *must* run
the compress operation once your database is populated with representative data.
> 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
>
> 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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