RE: RULE versus CHOOSE

Vivek,

In addition to Jon's excellent note, may I add that IOTs and Partitioned tables *will* need statistics. Missing stats will result in a guesstimate based on some parameters and queries involving such tables will take the wind out of the Development head's sail....

>> 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 .

Incorrect understanding and implementation of the CBO in preceeding years kept many away from it (including myself). This is probably the reason for the reluctance with this Team lead. Since he is willing to take responsibility, I would suggest that you set 'RULE', but collect stats anyway. Use these with badly performing queries and use these to 'convert' him..

John Kanagaraj

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Author: John Kanagaraj
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