Re: optimizer_index_cost_adj and optimizer_index_caching

Notes in-line

Regards

Jonathan Lewis
http://www.jlcomp.demon.co.uk

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----- Original Message ----- 
From: "Wolfgang Breitling" <breitliw@xxxxxxxxxxxxx>

: That is how I interpret it too, which is why I prefer using system_stats
: over changing o_i_c_a. There is a subtle difference between the way
o_i_c_a
: and system_stats achieve the apparently same goal:
:          o_i_c_a lowers the cost of index accesses compared to the
baseline
: whereas
:          system_stats increase the cost of full scans compared to the
baseline

Very good point

:
: I have not figured out yet if that can lead to differences in plan
: compositions or if it is guaranteed that the relative costs of  all plan
: components remain the same when comparing a plan stemming from having
: o_i_c_a=25 (i.e. single reads cost are 1/4 of multi read costs) vs. having
: system statistics where mreadtim = 4*sreadtim.
:

In theory it might - It would depend
on how Oracle handles the the "plus 1"
for tablescans in the new calculation.


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