RULE versus CHOOSE

Database = Oracle 8.1.7.0.0 on SunOS 5.6 . Current Database Size = 20 GB
This is only a Test One & the Live Production will be a BIGGER (100 GB) One .
OPTIMIZER_MODE = RULE & NO Statistics Exist Currently

Qs.1 How does optimizer_mode=CHOOSE Compare with RULE ?

Qs.2 Is there ANY Benefit of keeping optimizer_mode=CHOOSE WITHOUT having Any Statistics Existent on the Application Tables , Indexes ?

If Statistics are DELETED on ALL Objects , yet with optmizer_mode = CHOOSE , does it behave in Exactly the Same manner as having optmizer_mode set to RULE Or are there Still Some Advantages which can be Reaped ?

Qs.3 Are there any Disadvantages with Using RULE in 8.1.7.0 ?

Qs.4 In Choose mode are there any Commonly known Standard Important Statistics' Fields/Values which can be Looked at to understand why optimizer took a particular path ?
What Causes a Path to be Chosen in CHOOSE , we are largely ignorant about .

NOTE - At a Customer's Database , Our Development Section Head wants to set optmizer_mode=RULE & keep it so . His Reasons :-
- The path of the optimizer is more predictable when set to RULE

• Any under-performance Issues would be Handled by Giving HINTS etc rather than Allowing the Optimizer to Choose / Compute it's own Path which may be a BAD One .
• A Correct Path being Taken Today may in Time get Automatically Changed to a Worse Path somewhere in future (with the Stats getting OLD etc.) .
• Lastly his Team will Take Responsibility for Any Performance Issues arising out of a Code underperforming .

Qs Are there Any Best practices Documents / Links on RULE vs. CHOOSE ?

Qs. What do you Folks Advice ? Should I Given in to the 80-20 Rule Or Still Endeavour to persist for optimizer_mode=CHOOSE ?

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Author: VIVEK_SHARMA
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