http://www.dbms2.com/2007/12/29/optimizer-geekdom/ Choices in data management and analysis Sun, 20 Jul 2008 01:29:58 +0000 http://wordpress.org/?v=2.5.1 http://www.dbms2.com/2007/12/29/optimizer-geekdom/#comment-66068 Daniel Weinreb Sun, 30 Dec 2007 13:28:53 +0000 http://www.dbms2.com/2007/12/29/optimizer-geekdom/#comment-66068 According to the great theory of RDBMS's, if you have two queries that are written differently in the query language but have the same semantics, the optimizer should execute the same plan for both. With Oracle, this is far from true, and if you rephrase a query the "right" way, you can get huge performance increases. So you have to be an Oracle wizard to know that, which is one reason that there are Oracle wizards for hire, some at amazing hourly rates. I have been told about a product you can buy that takes Oracle queries and outputs equivalent Oracle queries that are faster; if their query optimizer were ideal, there would be no use for such a thing. I have heard that IBM's DB/2 has a much better optimizer in this regard, but this is all just from anecdotes. According to the great theory of RDBMS’s, if you have two queries that are written differently in the query language but have the same semantics, the optimizer should execute the same plan for both. With Oracle, this is far from true, and if you rephrase a query the “right” way, you can get huge performance increases. So you have to be an Oracle wizard to know that, which is one reason that there are Oracle wizards for hire, some at amazing hourly rates. I have been told about a product you can buy that takes Oracle queries and outputs equivalent Oracle queries that are faster; if their query optimizer were ideal, there would be no use for such a thing. I have heard that IBM’s DB/2 has a much better optimizer in this regard, but this is all just from anecdotes.

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