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https://issues.apache.org/jira/browse/DERBY-1907?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dag H. Wanvik updated DERBY-1907:
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Derby Categories: [Performance]
> Improve optimizer to prune query plans more aggressively.
> ---------------------------------------------------------
>
> Key: DERBY-1907
> URL: https://issues.apache.org/jira/browse/DERBY-1907
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 10.1.3.2, 10.2.1.6, 10.3.1.4
> Reporter: A B
>
> For large queries with numerous and deeply-nested subqueries like those in
> DERBY-1777, the number of different index/joinOrder/joinStrategy combinations
> that the optimizer can process is extremely high. In the absence of an
> efficient timeout mechanism (see DERBY-1906) this can lead to situations
> where the optimizer spends far too much time trying out different access
> paths before picking a plan. In the case of the DERBY-1777 queries, the
> optimizer can literally spend hours trying out all of the possible
> combinations before deciding on the best one.
> Even if/when the timeout mechanism is improved, it would still be great if
> the Derby optimizer could somehow figure out how to aggressively prune out
> access paths that are known (or suspected) to be sub-optimal. This way the
> optimizer would spend less time optimizing "bad" access paths and could
> therefore try out more "good" plans before timeout occurs.
> I have no idea how this pruning would occur, but I do think it would be
> extremely beneficial to the Derby optimization process when dealing with
> deeply nested queries with large FROM lists.
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