Examine the command to change a parameter value from the default to 50: SQL> ALTER
SYSTEM SET OPTIMIZER_INDEX_COST_ADJ = 50; What is the effect of changing the
value of the parameter?(Choose the best answer.)
A.
It influences the optimizer to use full table scans instead of index scans as the estimated
cost of full table scan is reduced.
B.
It influences the optimizer to use bitmap indexes as the estimated cost of conversion from
bitmap to rowid is reduced.
C.
It influences the optimizer to always use fast full index scans as the estimated cost of
using an index is reduced.
D.
It influences the optimizer to use indexes instead of full table scans as the estimated cost
of using an index is reduced.
Explanation:
http://www.dba-oracle.com/oracle_tips_cost_adj.htm
Reducing the OPTIMIZER_INDEX_COST_ADJ influences the CBO to prefer indexes.
D – right.
D
A –
OPTIMIZER_INDEX_COST_ADJ lets you tune optimizer behavior for access path selection to be more or less index friendly—that is, to make the optimizer more or less prone to selecting an index access path over a full table scan.
The default for this parameter is 100 percent, at which the optimizer evaluates index access paths at the regular cost. Any other value makes the optimizer evaluate the access path at that percentage of the regular cost. For example, a setting of 50 makes the index access path look half as expensive as normal.
D
default is 100
the more the value is low, the more indexes will be used and the less full scan will be used.
carlosegf, your comments are ok, but you take the wrong decision.