Re: hinting and the rule based optimizer
- From: "Daniel W. Fink" <Daniel.Fink@xxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Thu, 01 Apr 2004 15:06:07 -0700
Ryan,
If you have a multi-table query and you provide a valid hint that affects only
one of the table access paths, then the CBO will use the defaults for the rest
of the tables. I would venture to say that this is
probably what is killing your performance. Hints are only valid for the CBO
(does the RULE hint use the CBO engine to call the RBO engine?).
It seems to me that if you add a hint to a query against an unanalyzed database,
you need to add hints for each access path, join operation, etc.to make sure the
CBO follows the exact path you want. Essentially, you are creating a custom-RBO.
Daniel Fink
ryan.gaffuri@xxxxxxx wrote:
> We have a legacy 8.1.7.3 instance that is in RBO mode. My group does not own
> it, so we cannot change it to CBO.
>
> When I hint anything from an index to ordered, etc... it switches to the CBO
> and since nothing is analyzed, it's an even worse plan... Not allowed to
> analyze the tables either because it's not our property.
>
> Any rules around hinting the RBO in 8.1.7.3? Why would it switch to the CBO
> from a simple hint? I never use the RBO so please bare with me.
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