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How to find [message #526536]

Tue, 11 October 2011 08:57

9390512774
Messages: 103
Registered: January 2011
Location: hyd

Senior Member

Hi Experts,

When I am executing a query,

1.)how can I know, Whether its using RBO or CBO?

2.)If its using RBO then how to change it to use CBO?

3)Is RBO yields best performance or CBO yields Best performance?

Thanks in advance.

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Re: How to find [message #526542 is a reply to message #526536]

Tue, 11 October 2011 09:14

cookiemonster
Messages: 13904
Registered: September 2008
Location: Rainy Manchester

Senior Member

Use code tags for code. Not questions.

1) If it's 11g it'll be CBO. For 8i it depends on the optimiser mode parameter. Run an explain plan for the query. If it gives a cost figure you're using the CBO.
2) Change the optimiser mode parameter.
3) CBO - which is why oracle have got rid of the RBO.

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Re: How to find [message #526544 is a reply to message #526542]

Tue, 11 October 2011 09:20

BlackSwan
Messages: 26766
Registered: January 2009
Location: SoCal

Senior Member

>Is RBO yields best performance or CBO yields Best performance?
It depends.
Some SELECT were written to take advantage of RBO & when moved to DB using CBO perform badly

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Re: How to find [message #526546 is a reply to message #526542]

Tue, 11 October 2011 09:24

9390512774
Messages: 103
Registered: January 2011
Location: hyd

Senior Member

Quote:

1) If it's 11g it'll be CBO. For 8i it depends on the optimiser mode parameter. Run an explain plan for the query. If it gives a cost figure you're using the CBO.

How to change the optimiser mode parameter.
Where can we find this parameter

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Re: How to find [message #526548 is a reply to message #526546]

Tue, 11 October 2011 09:31

BlackSwan
Messages: 26766
Registered: January 2009
Location: SoCal

Senior Member

SQL> show parameter optimizer_mode

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Re: How to find [message #526561 is a reply to message #526546]

Tue, 11 October 2011 10:05

Michel Cadot
Messages: 68418
Registered: March 2007
Location: Nanterre, France, http://...

Senior Member
Account Moderator

9390512774 wrote on Tue, 11 October 2011 16:24

Quote:

1) If it's 11g it'll be CBO. For 8i it depends on the optimiser mode parameter. Run an explain plan for the query. If it gives a cost figure you're using the CBO.

How to change the optimiser mode parameter.
Where can we find this parameter

All parameters are described in Database Reference.
Bookmark it so you will have no more question on parameters.

Regards
Michel

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