Collecting system statistics in 9i is supposed to automagically do what optimizer_index_cost_adj does, at least if you set it according to the formula in Tim's paper ("The Search for Intelligent Life in the Cost-Based Optimizer"). The CBO then uses different cost factors for single-block IO (predominantly index accesses) and multiblock IO (table and index scans).

At 06:04 AM 7/30/2003 -0800, you wrote:
Hi all:

I have been reading on the optimizer_ parameters for
Oracle 9i - optimizer_max_permutation,
optimizer_index_caching and optimizer_index_cost_adj.
I have also been playing whith them and I can see that
they affect the explain plans for some queries quite
dramatically. Is there any guidelines for what they
should be set to for optimum performance (some kind of
range and may be relationship between the values) or
is this mostly a trial and error kind of thing? I have
seen a few discussion on the Oracle Metalink, but
mostly they are very specific  - try this value or try
that value. Does anyone have a link to a document with
something more systematic than that?

Wolfgang Breitling Oracle7, 8, 8i, 9i OCP DBA Centrex Consulting Corporation http://www.centrexcc.com


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