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From "Eric Radzinski (JIRA)" <derby-...@db.apache.org>
Subject [jira] Commented: (DERBY-855) Document optimizer overrides which were introduced in 10.2
Date Thu, 09 Feb 2006 17:38:59 GMT
    [ http://issues.apache.org/jira/browse/DERBY-855?page=comments#action_12365762 ] 

Eric Radzinski commented on DERBY-855:
--------------------------------------

How's this (only the second-to-last sentence is new):

joinStrategy
Use the joinStrategy property to override the optimizer's choice of join strategy.  The two
types of join strategy are called nested loop and hash. 
In a nested loop join strategy, for each qualifying row in the outer table, Derby uses the
appropriate access path (index or table scan) to find the matching rows in the inner table.
  In a hash join strategy, Derby constructs a hash table that represents the inner table.
For each qualifying row in the outer table, Derby does a quick lookup on the hash table to
find the matching rows in the inner table. Derby needs to scan the inner table or index only
once to create the hash table.  The -DERBY-PROPERTIES parameter must immediately follow the
inner table.  

Typically, you will use the joinStrategy property only in conjunction with the joinOrder property.
 Specifying a join strategy without knowing the join order can yield less-than-optimal results.

Valid values include HASH and NESTEDLOOP.  The joinStrategy property can be used only within
a TableExpression.



> Document optimizer overrides which were introduced in 10.2
> ----------------------------------------------------------
>
>          Key: DERBY-855
>          URL: http://issues.apache.org/jira/browse/DERBY-855
>      Project: Derby
>         Type: Sub-task
>   Components: Documentation
>     Versions: 10.2.0.0
>     Reporter: Mamta A. Satoor
>     Assignee: Eric Radzinski
>      Fix For: 10.2.0.0
>  Attachments: ctundepthoptover.html, ctunoptimzoverride.html, ctunoptimzoverride.html,
derby855-2.diff, derby855.diff, derby855_html_files.zip, tuning_guide.zip
>
> Optimizer overrides support in Derby was added as jira entry DERBY-573. Eric Radzinski
is working on the documentation part of the feature. This issue is to keep track of documentation
changes.

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