Optimizer change from 8i-9i

Hi, all,
    We will recently migrate some important database server from 8i to
9i(9.2.0.5 with a bunch of fixes). As we have very high concurrency
and load, we want to keep the optimizer the same behavior as our
existing 8i. We plan to set: optimizer_feature_enable=3D8.1.7 after the
migration. Maybe compatible=3D8.1.7 also.
    I have two questions here:
1. For SQLs using RBO, the plan for the existing SQL won''t change,
right? As oracle says no change for RBO since oracle 7.3.
2. For SQLs using CBO(as some feature will force CBO parsee), when the
optimizer_feature_enabled=3D817, and don't change any optimizer_related
parameters,  is it still possible for SQL to choose different plan in
9i as the old plan in 8i? (Maybe because of different Cost caculation
in 9i?)

Can some one with experience from 8i-9i share your experience?
Thanks


--=20
Regards
Zhu Chao
www.cnoug.org
--
http://www.freelists.org/webpage/oracle-l

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