Learn more about Oracle database instances

Oracle database is the world's leading relational database management system (RDBMS) and is widely used in enterprise-level systems. An instance of Oracle database is an important part of the database system. It includes memory structures and background processes for managing database operations. An in-depth understanding of Oracle database instances can help developers better optimize database performance and perform tuning work.

This article will introduce the related concepts and operations of Oracle database instances through specific code examples.

The concept of Oracle database instance

Oracle database instance is a working environment of Oracle database in memory, and each database has its own instance. The instance consists of SGA (System Global Area) and background processes.

SGA includes multiple components, such as Buffer Cache, Shared Pool, Redo Log Buffer, etc., which are used to manage data and metadata in memory. Background processes include PMON (Process Monitor), SMON (System Monitor), DBWn (Database Writing Process), etc., which are used to manage various operations of the database.

Create an Oracle database instance

To create an Oracle database instance, you first need to install the Oracle database software. Next, you can create a database instance through the DBCA (Database Configuration Assistant) tool provided by Oracle. The following is an example of manually creating an Oracle database instance through SQL statements:

CREATE DATABASE my_database
   USER SYS IDENTIFIED BY my_password
   USER SYSTEM IDENTIFIED BY my_password
   LOGFILE GROUP 1 ('/u01/oracle/my_database/redo01a.log')
            SIZE 100M BLOCKSIZE 512,
          GROUP 2 ('/u01/oracle/my_database/redo02a.log')
            SIZE 100M BLOCKSIZE 512,
          GROUP 3 ('/u01/oracle/my_database/redo03a.log')
            SIZE 100M BLOCKSIZE 512
   MAXLOGFILES 5
   MAXLOGMEMBERS 5
   MAXLOGHISTORY 1
   MAXDATAFILES 100
   MAXINSTANCES 1
   CHARACTER SET AL32UTF8
   NATIONAL CHARACTER SET AL16UTF16
   DATAFILE '/u01/oracle/my_database/system01.dbf' SIZE 325M REUSE
   EXTENT MANAGEMENT LOCAL
   SYSAUX DATAFILE '/u01/oracle/my_database/sysaux01.dbf' SIZE 325M REUSE
   DEFAULT TABLESPACE users
      DATAFILE '/u01/oracle/my_database/users01.dbf'
      SIZE 500M REUSE AUTOEXTEND ON MAXSIZE UNLIMITED
   DEFAULT TEMPORARY TABLESPACE temp
      TEMPFILE '/u01/oracle/my_database/temp01.dbf'
      SIZE 20M REUSE
   UNDO TABLESPACE undotbs
      DATAFILE '/u01/oracle/my_database/undotbs01.dbf'
      SIZE 200M REUSE AUTOEXTEND ON MAXSIZE UNLIMITED;

Connecting to an Oracle database instance

To connect to an already created Oracle database instance, you can use tools such as SQL*Plus. The following is an example of connecting to an Oracle database instance:

sqlplus sys/my_password as sysdba

View Oracle database instance information

To view information about an Oracle database instance, you can use the following SQL statement:

SELECT instance_name, host_name, version, startup_time
FROM v$instance;

Close Oracle Database instance

To shut down the Oracle database instance, you can use the following SQL statement:

SHUTDOWN IMMEDIATE;

Summary

Through the above code examples, we have a deeper understanding of the Oracle database instance . Oracle database is a powerful database management system. Through in-depth study and practice, we can better master database optimization and tuning skills, improve system performance, and provide better support for the development of enterprises. I hope these examples can help readers better learn and apply knowledge related to Oracle database instances.

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