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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4327) Implement optimizer support for bushy trees.
Date Mon, 07 Feb 2011 13:32:30 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4327?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12991376#comment-12991376
] 

Rick Hillegas commented on DERBY-4327:
--------------------------------------

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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