My Oracle Notes (1): Oracle Architecture Overview

From today on, I started to prepare a system to learn about Oracle. In addition to meeting the urgent needs of my work, I also hope to have a good understanding of the profound and profound knowledge of Oracle Database.

Now, I used to write SQL statements for Oracle applications, or use JDBC or other encapsulated database access libraries in Java to call stored procedures written by others. This is really superficial.

OK. Go to the topic.

Today, I will start with Oracle's architecture and look at the entire composition of Oracle. This is a good picture of the description of the Oracle database architecture that can be found on the Internet, it comes from <Oracle9i Database Administration Fundamentals I>:

 

From this figure, we can roughly see the interaction between various components of the Oracle database. Below we will explain some of the most important components and concepts in this architecture.

What is Oracle Server?

Oracle Server is a big concept. It refers to the database management system used for information management. <Fundamentals I> gave him a very formal definition: a database management system that provides an open, comprehensive, integrated
Approach to information management.

An Oracle Server is composed of two parts: Oracle Instance and Oracle Database.

What is Oracle Database?

Oracle Database is actually a collection of data files. It contains three file types:

(1) Data Files contains the actual Data in the database.

(2) Online Redo Log Files: Online Redo logs record database data changes and can be used to restore data.

(3) Control Files: the Control file contains information to maintain and verify database integrity.

Other important files (but they are not part of Oracle Database) include:

(1) Parameter File: records some database Parameter information, such as startup parameters and SGA size.

(2) Password File

(3) Archived Redo Log Files: after all, the size of online Redo logs is limited. When all logs are full, there are two choices, the first is to erase the previous online redo logs from the beginning and continue writing. The second is to back up the previous online redo logs first, then, a new online Redo File is written for the erased logs. The online Redo Log of this backup is Archived Redo Log Files ).

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What is an Oracle Instance?

Oracle Instance is a way to access Oracle Database. The relationship between instances and databases is many-to-one. One Instance can only access one Database, and one Database can access multiple instances, such as Oracle RAC.

The Instance is composed of the SGA memory and Backgroud Process, for example:

 

From the figure "Overiew of Primary Components" and the Instance structure, we can see three processes: User Process, Server Process, and Background Process. What are the differences between these three processes, I will study it in the next article.