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From "Rick Hillegas (JIRA)" <derby-...@db.apache.org>
Subject [jira] Commented: (DERBY-573) Provider support for optimizer overrides in Derby.
Date Mon, 19 Sep 2005 19:37:28 GMT
    [ http://issues.apache.org/jira/browse/DERBY-573?page=comments#action_12329897 ] 

Rick Hillegas commented on DERBY-573:

It sounds as though this syntax will not allow the parser to catch typos and that if the user
makes a mistake, the parser will silently do the wrong thing. I'm not a big fan of silent

Why prefer an Oracle-style, comment-based approach to Sybase-style, parser-checked optimizer
hints? Is it because we hope that we can run the same query against Oracle and Derby by simply
seeding the query with two sets of comments, one for each database? I don't understand the
value of this flexibility. If the application really is going to run against two databases,
then the developers will have to build a sql-portability layer anyway. In that case, queries
won't be hard-coded: they will be constructed by a code generator. The code generator will
have to be smart enough to handle other differences between the databases and it's no additional
trouble for the code generator to emit database-specific optimizer hints.

> Provider support for optimizer overrides in Derby.
> --------------------------------------------------
>          Key: DERBY-573
>          URL: http://issues.apache.org/jira/browse/DERBY-573
>      Project: Derby
>         Type: New Feature
>   Components: SQL
>     Versions:
>     Reporter: Mamta A. Satoor
>     Assignee: Mamta A. Satoor
>  Attachments: optimizeroverrides.html
> Derby's query optimizer usually makes the best choice of join order and access path.
The default join strategy ususally works the best too. However, there are some cases in which
user may want to override the optimizer or the default values. Providing support for optimizer
overrides will allow users to hand-tune the optimizer for queries. 

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