The query executor runs an established query execution plan. It works with the storage engine to read or write the required data, while other components manage transactions, locks, and cached pages. section 1.2.1
Avoid treating plan execution as independent from surrounding SQL Server choices:
- Poorly written T-SQL, cursors, or unmaintained statistics and indexes can hinder the optimizer before a plan reaches the executor. section 1.2.1
- Transaction isolation affects performance, while locking preserves transactional consistency; NOLOCK can expose rows that were never committed. section 1.2.1
- Plan cache can let later executions avoid optimization, and buffer cache supplies data pages instead of direct disk reads. section 1.2.1
A product lookup
A parameterized SELECT against dbo.Products can execute through the established plan, retrieve rows through the storage engine, and use NOLOCK—but that hint may return uncommitted data. section 1.2.1
