Database Scanning Methods

You have learned that all database operations are carried out by database management systems (DBMSs) such as PostgreSQL. Typically, the DBMS will run these operations in a server's memory, which stores the data to be processed. The problem with this approach is that memory storage is not large enough for modern databases, which are frequently in a scale of gigabytes, if not terabytes. Data in the majority of modern databases is saved on hard disks and uploaded into memory when it is used in a database operation. Yet again, a DBMS can only upload a small part of the database into memory. Whenever it figures that it needs a certain dataset, it must go to the hard disk to retrieve the unit of storage (which is called a hard disk block) that has the required data in it. The process that the PostgreSQL server uses to search through a database is known as scanning.

SQL-compliant databases, such as PostgreSQL, provide several different methods for scanning...