There is a bug in 11.2.0.2 and 11.2.0.3 that causes worse plan.
need to add hint
/*+OPT_PARAM('_optimizer_use_feedback','false') */
to resolve the issue.
symptom:
first run --fast
second and onward runs --very slow
do 10046, you will see a lot of physical reads
query on v$sql, you will see the plan_hash_values are different.
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