Introduction to Oracle Database and Instance

Introduction to Oracle Database and Instance
Introduction to Oracle Database and Instance

• Database: it consists of a series of files stored on the disk. These files are used to store data.
• Database instance: it consists of a series of memory structures for managing database files, including a shared memory area named system global area (SGA) and a series of background processes.

Oracle Instance and Database

Oracle Database

Oracle Database is a collection of data. Oracle processes the data as a complete unit. Oracle Database, also known as the physical structure of Oracle, provides real physical storage for the Database.

Oracle Database consists of three types of files:

 

• Control files: contains the database name, physical structure information of the database, and information required to maintain and verify Database Consistency.
• Online redo log files: contains the changes in the data to be recorded after the system crashes.
• Data files: contains data stored in the database.

Oracle Instance

 

An oracle instance is a mechanism for accessing databases. It consists of a memory structure and a series of background processes.

Five processes required for running the instance: SMON, PMON, DBWR, LGWR, and CKPT.

If one of the preceding five processes stops, the Oracle instance is automatically disabled.