RBO
The RULE BASED Optimizer in future called RBO, was the first Optimizer Implementation of Oracle. It’s main design was set up based on static ranking rules of access pathes :
- ROWID Access - always best
- Primary Key access - always very good
- Non Unique Index - always good
- FULL TABLE SCAN - always bad
The Model based on ranking rules could get into conflict with the number rows an operation has to process.
To be continued …
This could result in very bad execution plans.
Further documentation :
http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96533/rbo.htm#38893