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Home -> Community -> Mailing Lists -> Oracle-L -> Re: good value for optimizer_index_cost_adj
It's interesting that you should have heard that.
My first interpretation of the optimizer_index_cost_adj was that it was an estimate of the table logical I/O that would become physical I/O (and ignore the fact that this was allowed to go above 100%) - which brings it into line, somewhat, with the optimizer_index_caching in terms of 'addressing the same issue'.
However, I decided that your interpretation was a much nicer, more intuitive, way of appreciating the significance of the number and deciding on a rational setting for it.
But I'm inclined to agree with you - even if they were supposed to be addressing the same problem in different ways, they do seem to be jointly and separately (as the lawyers say) viable.
Have you tried any experiments yet which mix dbms_stats.system_stats figures with the effects of these two parameters ? That ought to be a case of when we should do one or the other.
Jonathan Lewis
http://www.jlcomp.demon.co.uk
Author of:
Practical Oracle 8i: Building Efficient Databases
Next Seminar - Australia - July/August
http://www.jlcomp.demon.co.uk/seminar.html
Host to The Co-Operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.html
-----Original Message-----
At IOUG-A, I heard discussion that the OPTIMIZER_INDEX_CACHING and
OPTIMIZER_INDEX_COST_ADJ were two separate approaches developed by
different
development teams within Oracle that had the exact same purpose. So,
the
argument was advanced that setting *either* one *or* the other was
sufficient, but not *both*. Not having any access to the internal
goings-on
in Oracle ST Development, I'm sticking with the idea that these two
parameters are addressing *different* and very specific issues, so
they both
should be considered and used independently of one another...
I have a paper on this topic at
http://www.EvDBT.com/SearchIntelligenceCBO.doc that discusses these
issues
in more depth...
--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Jonathan Lewis
INET: jonathan_at_jlcomp.demon.co.uk
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