Microsoft® SQL Server® 2008 Internals

Optimizer Architecture

The Query Optimizer contains many optimization phases that each performs different functions. The different phases help the Query Optimizer perform the highest-value operations earliest in the optimization process.

The major phases in the optimization of a query, as shown in Figure 8-14, are as follows:

• Simplification

• Trivial plan

• Auto-stats create/update

• Exploration/implementation (phases)

• Convert to executable plan

Figure 8-14. Query Optimizer pipeline

Before Optimization

The SQL Server query processor performs several steps before the actual optimization process begins. These transformations help shape the tree into a form about ...