Architecture of ORACLE 9i Database Server

2.4.1 Process Structure
There are two types of processes in the Oracle 9i network environment.
1. User Process
A user process is a program running on the client memory, such as the SQL Plus and enterprise controller run on the client. The user process sends an operation request to the server process.
2. server process
The main server processes are shown in Table 2.5.
Table 2.5 main background support process names of Oracle 9i mainly apply to recovery when the system monitoring process (SMON) database system is started, and recover the process monitoring process (PMON) for faulty Databases) recover Failed User process database write process (DBWR) write the modified data block content back to the Database Log write process (LGWR) write the log Content in the memory into the log file archive process (ARCH) when the database server runs in archive mode, the process is called to complete the log archive Checkpoint Process (CKPT) to identify the checkpoint, which is used to reduce the time required for database recovery (RECO) LCKn is used in distributed databases to ensure data consistency in Parallel Server mode. The snapshot process (SNPn) is used to refresh and schedule snapshots (Dnnn) route user processes to available server processes for processing 2.4.2 Memory Structure
1. system global zone (SGA)
As shown in SGA2.47.

2. Program global zone (PGA)
PGA is a dedicated memory area allocated to a single user process in the memory of the database server. It is private to the user process and cannot be shared.
2.4.3 logical structure of the database
The logical structure of the Oracle 9i Database mainly refers to the composition of the database from the perspective of the database user, as shown in Figure 2.48. From bottom up, there are six layers in the logical structure of the database.

1. Data Block)
2. Data Extent)
3. Data Segment)
4. Logic Object)
5. Table space)
After Oracle 9i is installed, nine default tablespaces are automatically created, as shown in Table 2.6.
Table 2.6 The default tablespace name of the Oracle 9i Database mainly uses CWMLITE for Online Analytical Processing (OLAP) DRSYS to store information related to workspace settings EXAMPLE instance tablespaces and store instance information INDEX tablespaces, stores database index information SYSTEM tablespaces, stores tablespace names, data files, and other governance information TEMP temporary tablespaces, and stores temporary table TOOLS tablespaces, store the UNDOTBS tablespace required by the database tool software, store the database recovery information USERS user tablespace, and store user private information. 6. database)
2.4.4 database storage structure
The database storage structure refers to how the logical structure is physically implemented. There are three layers in total, as shown in Figure 2.49.

1. Physical Block
2. physical files
Each physical file consists of several physical blocks, including data files, control files, and log files.
Data File: used to store all data with the DBF extension.
LOG File: records all operations performed on the database, with the LOG extension.
Control File: records the control information of all database files, with the CTL extension.
Taking the author's installation environment as an example, the main physical files of the database named "myoracle. mynet" are stored in c: \ oracle \ oradata \ myoracle, as shown in Figure 2.50.

2.4.5 overall structure of the database server
The overall structure of the Oracle 9i Database Server is shown in Figure 2.51.