PostgreSQL Administration Essentials

Understanding the concept of execution plans

It is impossible to understand the use of indexes without understanding the concept of execution plans. Whenever you execute a query in PostgreSQL, it generally goes through four central steps, described as follows:

• Parser: PostgreSQL will check the syntax of the statement.
• Rewrite system: PostgreSQL will rewrite the query (for example, rules and views are handled by the rewrite system).
• Optimizer or planner: PostgreSQL will come up with a smart plan to execute the query as efficiently as possible. At this step, the system will decide whether or not to use indexes.
• Executor: Finally, the execution plan is taken by the executor and the result is generated.

Being able to understand and read execution plans ...