User's Guide
PART 4. Database Administration and Advanced Use
Once each query is parsed, the optimizer analyzes it and decides on an access plan that will compute the result using as few resources as possible. This chapter describes the steps that the optimizer must go through to optimize a query. It begins with the assumptions that underlie the design of the optimizer, then proceeds to discuss selectivity estimation, cost estimation, and the other steps of optimization.
Update, insert, and delete statements must also be optimized, but the focus of this chapter is on queries. The optimization of these other commands follows similar principles.
The role of the optimizer
Steps in optimization
Reading access plans
Underlying assumptions
Physical data organization and access
Indexes
Predicate analysis
Semantic query transformations
Selectivity estimation
Join enumeration and index selection
Cost estimation
Subquery caching