Which DBMS feature identifies possible ways to execute the query and chooses the fastest query plan?

Which DBMS feature identifies possible ways to execute the query and chooses the fastest query plan?

• A. query cost
• B. query hint
• C. query optimizer
• D. operational information

Answer: (C)

The query optimizer is responsible for identifying possible ways to execute the query and choosing the fastest plan. It considers different execution strategies—such as which indexes to use, the order of joins, and which join methods (like nested loop, hash join, or merge join) to apply. By using statistics about the data (row counts, value distributions, index selectivity) it estimates the cost of each feasible plan in terms of I/O, CPU, and memory. After evaluating the viable options, it selects the plan with the lowest estimated cost and passes that plan to the execution engine. This is what makes query optimization crucial for fast, efficient query processing. Briefly, a query cost is a metric used during this evaluation, not the component that performs the optimization; a query hint is just a directive to influence the optimizer’s choice; operational information doesn’t carry out or decide on execution plans.

The query optimizer is responsible for identifying possible ways to execute the query and choosing the fastest plan. It considers different execution strategies—such as which indexes to use, the order of joins, and which join methods (like nested loop, hash join, or merge join) to apply. By using statistics about the data (row counts, value distributions, index selectivity) it estimates the cost of each feasible plan in terms of I/O, CPU, and memory. After evaluating the viable options, it selects the plan with the lowest estimated cost and passes that plan to the execution engine. This is what makes query optimization crucial for fast, efficient query processing.

Briefly, a query cost is a metric used during this evaluation, not the component that performs the optimization; a query hint is just a directive to influence the optimizer’s choice; operational information doesn’t carry out or decide on execution plans.