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https://issues.apache.org/jira/browse/DERBY-4327?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12991376#comment-12991376
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Rick Hillegas commented on DERBY-4327:
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Hi Nirmal,
My sense is that this is a tricky issue with a large risk of destabilizing
existing applications. The fallout from this change would be felt over many
subsequent releases. I would not recommend this as a GSoC project or as
someone's first 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
>
> 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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