How the database Oracle works

The working principle of the database, including the processing and architecture of the database system. In order to use the database, the process of the database system must be connected to the database. When a user runs a program (such as SQL*Plus), a user is actually started automatically on the client computer and the connection request is sent to the server over the network. The database on the server will derive a corresponding server process for the user process. The processing process of the database system is as follows: 1. The processing process can be simply described as: 2. The user runs the Oracle-based application program on his computer, that is, starts user process. 3. Establish a connection (CONNECT) between the client and the server. 4. On the basis of establishing the connection, establish a session (SESSION) for the user, and create a PGA area (Program Global Area) for the session to store information related to the session. In the same connection, different users have different sessions. 5. Start the server, and the server process is responsible for performing various tasks of the session. 6. The user process sends a statement. 7. The server process parses, compiles, executes the statement, and then writes the result to the database and returns it to the user process. 8. The user process receives the returned SQL execution result. 9. Display the SQL execution result in the application. Overall structure From the perspective of function and working principle, the overall structure can be divided into three parts, as shown in the figure below: Among them: ◆ Memory structure: including SGA and PGA. The most used memory is SGA, which is also the largest parameter of database performance. ◆ Process structure: including foreground process and background process. The foreground process refers to the service process and the user process. The foreground process runs according to actual needs and ends as soon as the need ends. Background processes refer to several processes that are automatically started after the Oracle database is started. ◆ Storage structure: including control files, data files, log files and other operating system files. The routine of Oracle data consists of SGA and background process.