Lesson 1

If you have reached this point in your Oracle training you have heard the terms instance and database. In Oracle land, when is an instance a database?
The anser is never. In this module, we will review the components of the instance (memory structures and processes) and the database (files stored on disk).
As users, we talk to the instance, not the database. An Oracle database is not readable, unless there is an instance to talk to it. The database ORCL will always and forever be ORCL. The instance that you use to access the database, however, can change. Our role as Oracle DBAs is to make sure the database will be available for normal access by our user community. We care about the instance only to the point that we use it to backup and recover our database. If the instance dies, we will start another one. If the database dies, that is another story, as we will discover during this course. By the end of this module you will be familiar with the following topics:

1. Oracle instance
2. Oracle memory structures
3. Oracle processes
4. How LGWR, ARCH, DBWR, and CKPT work
5. Oracle database file structures

This module will not cover all the subtleties of these topics. Our primary goal in this module is to cover these topics from a high-level perspective. Our understanding will then allow us to formulate a good backup and recovery plan. So let's get on with our investigation of Oracle memory, processes, and files.

An Oracle instance is made up of several components that work together to manage the database. These components include:

1. Memory Structures: The instance contains several memory structures that are used to store and manage data, including the System Global Area (SGA) and the Program Global Area (PGA).
2. Background Processes: These are the processes that run in the background and perform various tasks such as managing the buffer cache, managing the redo logs, and managing the shared pool. Some examples of background processes include the Database Writer (DBWR), the Log Writer (LGWR), and the Process Monitor (PMON).
3. Database Files: These are the files that make up the physical structure of the database, including datafiles, control files, and redo log files.
4. Network Services: The instance uses network services to allow clients to connect to the database, including the Listener and the SQL*Net protocol.
5. Oracle Database Services: The instance includes several services that are used to manage and access the data in the database, including the Oracle Database Service and the Oracle RAC Service.
6. Oracle Scheduler: The Oracle Scheduler is a feature that allows the DBAs to schedule and automate tasks, such as backups, report generation, and maintenance jobs.
7. Oracle Data Pump: Data Pump is an Oracle utility that allows you to move data between databases and schemas, it can also be used to export and import data in a logical or physical way.

All these components work together to manage the database and provide access to the data stored in the database, allowing clients to connect, query, and manipulate the data stored in the database.
The next lesson reviews Oracle instance structures.