Oracle DB versions: 10.2, 11.2, 12.2, 18c, 19C
I am going through the basics of Cost based optimizer and Rule based optimizer.
When using CBO (the default since 10.1), Oracle assesses various access paths and it chooses the 'least expensive' one.
Is it safe to assume that the cost is calculated based on Disk I/O operations that need to be performed for a particula access path ? This in turn, involves CPU calculation as well because Disk I/Os need CPU.
Regarding 'Rule' in Rule Based Optimizer:
Can the below one considered a 'rule' in RBO ?
If an index is available on a table the RBO rule is to always use the index based access path.