Three steps of Oracle Database startup: nomount, mount, and open

Three steps of Oracle Database startup: nomount, mount, and open

Three steps of Oracle Database startup: nomount, mount, and open

Conn sys/sys as sysdba
Shutdown abort;
Startup nomount;
Select instance_name, status from v $ instance;

Bringing the database to the mount status
Select value from v $ spparameter where;
Alter database mount;
The database Mount process is to read the control file described in the parameter file, verify the correctness of the control file, read the content of the control file into the memory, and mount indicates mounting, is a concept in the operating system. after mounting, a meaningless instance is connected to a database. because the instance is an empty shell. there is no relationship between the database and the instance. We can understand that the instance is a water pump and the data will be extracted from the pool to which the instance is stored. The instance is generic. mount refers to placing a general-purpose water pump into a designated pond.
Mount is a read control file that contains information about data files and log files.
Select instance_name, status from v $ instance;

Open Database
Alter database open;
The data file described in the read Control File
Verify the consistency of the data files. If they are inconsistent, use the log file to restore the database files to the consistent state.
After the database is open, normal users can access the tables of database users before they are visible.
Read-Only open Database
Alter database open read only;
Select OPEN_MODE from v $ database;
The default open mode is read write.
To change read only to read write, the database must be restarted. Now let's look at the three steps of database startup. We read the parameter file first, and we can write the parameter file here. after reading the parameter file, I read the control file. The control file describes the information of the data file and log file. If the control file is lost, you can create a new one. Finally, you can read the data file. our data is stored in the data file. database startup is divided into three steps, so that we can accurately know where there is a problem and quickly eliminate it. it's a bit like a mouse dragging the wood, and the big head is behind it. from the first 1 k parameter file to several t large databases. when we only call startup without adding any parameters. the default value is open, which is equal to startup open;
SQL> startup
Oracle instance started.

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