Do you agree with the definition of a clustered index and its role in a database?

A clustered index is an index that determines the physical order of storage of rows in a table. In a database with a clustered index, the table data is ordered by the key of this index.

Role of a clustered index:

• Accelerates key-based searches because data is stored in order.
• Useful for range queries where order matters.
• In PostgreSQL, a clustered index is created using the CLUSTER command, but the physical order is not automatically maintained during inserts/updates.

It is important to understand that in some DBMSs (e.g., MS SQL Server), a clustered index is the primary way of storing data, whereas in PostgreSQL, it is more of a table ordering operation by index, which is not maintained constantly without re-execution.