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https://issues.apache.org/jira/browse/DERBY-4327?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15032158#comment-15032158
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Rick Hillegas commented on DERBY-4327:
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I would repeat the feedback which I gave to Nirmal five years ago: I do not
recommend this issue as an introduction to the Derby optimizer. Thanks.
> Implement optimizer support for bushy trees.
> --------------------------------------------
>
> Key: DERBY-4327
> URL: https://issues.apache.org/jira/browse/DERBY-4327
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Reporter: Rick Hillegas
> Labels: derby_triage10_10
>
> Currently, the optimizer only considers left-deep trees. For queries
> involving many tables, the best plan may be bushy. In this email thread, a
> user notes poor performance by Derby on queries involving 5 or more tables:
> http://www.nabble.com/Slow-performance-on-5-or-more-joins-in-a-star-schema-tt24708686.html
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