Home » RDBMS Server » Performance Tuning » Rule based but has cost in explain plan.. why?
Rule based but has cost in explain plan.. why? [message #236976] Fri, 11 May 2007 08:34 Go to next message
beetel
Messages: 96
Registered: April 2007
Member
One of our schema is using Rule-based optimizer. When I tried get the explain plan for a query, the Cost column in the Explain plan has values. The table has no statistics as I saw in the LAST_ANALYZED column of the following views:

- USER_TABLES
- USER_INDEXES
- USER_TAB_PARTITIONS

The LAST_ANALYZED column is null. And it has no entry in the USER_TAB_COL_STATISTICS table, too.

My question is how can there be a cost in the explain plan if the table has no statistics at all because it uses rule-based optimizer...
Re: Rule based but has cost in explain plan.. why? [message #236978 is a reply to message #236976] Fri, 11 May 2007 08:37 Go to previous messageGo to next message
Michel Cadot
Messages: 64132
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
Are you sure it uses RBO?
Post the proof.

Regards
Michel
Re: Rule based but has cost in explain plan.. why? [message #237032 is a reply to message #236976] Fri, 11 May 2007 12:15 Go to previous messageGo to next message
michael_bialik
Messages: 611
Registered: July 2006
Senior Member
Do you have hints in your query?
Any hint (except RULE) invokes CBO.

HTH.
Michael
Re: Rule based but has cost in explain plan.. why? [message #237514 is a reply to message #237032] Mon, 14 May 2007 13:45 Go to previous message
jrich
Messages: 35
Registered: February 2006
Member
If you are using an object the RBO does not support, such as partitioned tables, bitmap indexes, IOTs, or function-based indexes, then the CBO will be used.

JR
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