Re: Why would an index not be used if specified as a hint in a query?

On 13 Feb 2005 16:44:15 -0600, Galen Boyer <galenboyer_at_hotpop.com> wrote:

>I thought hints lowered the cost of a particular access path.

They don't.
Many people complaining about CBO not 'obeying' hints have optimizer_index_cost_adj on it's default of 100 (index scan is as expensive as reading a table) and/or optimizer_index_caching on it's default value of 0 (indices are never cached) Now, changing these setting truly lowers the cost of the index access path.

I also think an OBO is a bad idea. It would simply mean people are going to ignore the wisdom of the optimizer, and are simply going to hint every statement. Something which Thomas Kyte in his seminar advises against doing.

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Sybrand Bakker, Senior Oracle DBA