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What are the different startup modes for an Oracle database (NOMOUNT, MOUNT, OPEN)?
What are the different startup modes for an Oracle database (NOMOUNT, MOUNT, OPEN)?
Jul 01, 2025 am 12:32 AM
The Oracle database startup process is divided into three modes: NOMOUNT, MOUNT and OPEN. 1. NOMOUNT mode is the first stage of startup. It only reads parameter files and allocates memory structures, and does not access data files or control files. It is suitable for creating a new database or recovering corrupt control files; 2. MOUNT mode loads the control file but does not open the data file, and can perform operations such as archive log settings modification or data file recovery; 3. OPEN mode opens all data files and redo log files, and the database is accessible to users. It supports READ ONLY or READ WRITE options to ensure the normal operation of the application.
The Oracle database startup process is divided into several different modes: NOMOUNT, MOUNT and OPEN. Each schema has its own specific uses and applicable scenarios, and understanding the differences between them is essential for database management.
NOMOUNT mode
This is the first phase of database startup. At this stage, Oracle only reads parameter files (such as SPFILE or PFILE) and allocates the memory structure while starting the background process. At this time, the database will not access the data file or control file, so any tasks related to specific database operations cannot be performed.
Common uses include:
- Create a new database
- Recover corrupt control files
The command to enter NOMOUNT mode is:
STARTUP NOMOUNT;
MOUNT mode
During this stage, Oracle loads the database's control file, but still does not open the data file. This means you can perform some operations involving logical structures, such as enabling or disabling archive log mode, restoring data files, etc.
Typical application scenarios include:
- Database recovery
- Modify archive log settings
To enter MOUNT mode, you can use the following command:
STARTUP MOUNT;
Or switch from NOMOUNT state to MOUNT:
ALTER DATABASE MOUNT;
OPEN mode
This is the normal state of the database. In this mode, all data files and redo log files are opened and the database is accessible to users. Typically, the database administrator wants the system to end up in this state to support the normal operation of the application.
Additional options in OPEN mode:
- READ ONLY : Querying is allowed but writing is prohibited.
- READ WRITE : Default mode, allowing full access to the database.
Starting the database to OPEN mode can be directly passed:
STARTUP;
You can also switch from MOUNT mode to OPEN:
ALTER DATABASE OPEN;
In general, these three modes constitute the complete startup process of Oracle database, which is basically all. Mastering their differences and how to use them correctly will help better manage and maintain the database environment.
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