Re: i/o parameters on oracle and sun

Viacheslav Leichinsky wrote:
>
> In article <3A643625.979_at_yahoo.com>,
> connor_mcdonald_at_yahoo.com wrote:
> > Yes - the larger the multiblock the more scans tend to be preferred.
 If
> > you're app has more of dependency on nested loop performance, then
 could
> > consider an optimiser mode of first_rows in init.ora or selected
> > sessions.
>
> Hello,
>
> you mustn't set optimiser_mode=first_rows in init.ora
> because queries on SYSTEM tablespace have optimized for RBO (not CBO).
>
> Regards,
> Slava.
>
> Sent via Deja.com
> http://www.deja.com/

I do not believe that this is the case - recursive SQL's are treated differently, I'm pretty sure the rule is:

db setting              recursive sql will use
RULE                     RULE
CHOOSE                   CHOOSE
FIRST_ROWS               CHOOSE
ALL_ROWS                 CHOOSE

and thus (as long as you don't analyze the data dictionary), then correct data dictionary access will remain.

HTH
Connor

-- 
===========================================
Connor McDonald
http://www.oracledba.co.uk (mirrored at
http://www.oradba.freeserve.co.uk)

"Some days you're the pigeon, some days you're the statue"