Hello,
3 questions:
1. What is the meaming of
_optimizer_cost_based_transformation
and
_optimizer_push_pred_cost_based
parameters?
2. What is the consequences of setting the either one on the instance level?
3. Is there an info source about hidden parameters, those starting with _ ?
IMHO there are at most two occasions to set hidden parameters:
1. when Oracle Support tells you to
2. when you know enough about them not to need to ask.
and the second is debateable.
Not only. If setting one of such undocumented parameters is the only solution given for a certain bug (Oracle support doesn't have to say it in loud, - it's in the corresponding NOTE in Metalink). Furthermore, Oracle doesn't tell you to fix DD inconsistencies, so you don't do it? Or do it carefully and encounter no problems whatsoever? Working on the based tables (or whatever they're called) like sys.obj$ is not recommended by Or.Supp. but I've done it multiple times when it was the only solution.
Anyway, in my case the reason is bug 4648181, the only solution for which (according to Oracle certainly) is:
Workaround:
Set _optimizer_cost_based_transformation = off
OR
Set _optimizer_push_pred_cost_based = false
(Note:4380992.8)
I don't like how "optimizer cost based transformation = OFF" sounds.
Especially when applied on system level. The second one I couldn't draw guess upon. That's why I need its detailed explanation, which still can't find anywhere. So, once again, does someone know the description or the location of the descriptions of the hidden ora parameters?