CHAPTER 6Getting the Most Out of the Cost-Based Optimizer
For over a decade, Oracle has provided two optimizers: the rule-based optimizer (RBO) and the cost-based optimizer (CBO).
With the RBO, query plans are generated according to a predefined set of rules. It is possible to look at a query and, with knowledge of the tables and indexes in place, predict with 99.9% accuracy what the query plan will be. There are possible differences in query plans based on the order of index creation when two indexes “tie” with each other, meaning either index satisfies the rules. But in general, in a database, once you see the query plan for a rule-based optimized query, that query plan will persist. The query plan is generated by a very well-defined, rigid ...
Get Effective Oracle by Design now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
