Re: how does CBO handle old statistics

You need to follow a good tuning methodology to figure out what is going on. I'd recommend Cary Milsap's book. In the meantime, if you can get ahold of OEM, you can drill down from the Top SQL's to the explain plan, to figure out what indexes you are missing or what-all. Of course, if you know which queries are a problem, explain or trace those first. If rule-based is faster, you are (well, the code is) probably doing something wrong. Perhaps the optimizer_index_caching and optimizer_index_cost_adj init.ora parameters are off.

Definitely check out the concepts and performance tuning guides at tahiti.oracle.com.

You also might consider patching, depending on your platform.

jg

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