In this tutorial we learn about startup concept of oracle database. There are different stage to startup oracle database.without startup oracle instance we can not access oracle database.
Different stages for startup oracle database:
There are three stages to startup oracle database.these stages are described below.
Nomount stage:-- this is the first stage to startup oracle database. Some tasks occured during this stage these are described below.
1. In this stage oracle reads parameter file from the default location.it also reads if you mention the location along with the startup command other wise it reads from the default location.
2. During the nomount stage oracle allocates SGA and starts all required background processes.
3. In this stage oracle database is not attached with the oracle instance.
In this stage we use this below command in SQL promt.
SQL> startup nomount;
Mount stage:-- This is the second stage to startup oracle database.Some tasks also occured during this stage.
1. During this stage oracle reads the control file and finds the location of the datafiles which is written in the control file.
2. During this stage oracle tries to open the datafiles.
3. Also it the database recovery stage if your database crashes by any reason you can recover at this stage.
4. During this stage oracle database attached to the oracle instance.
5. This stage is the maintainance stage for a database administrator.
6. Only database admin can access database .no one can access oracle database during this stage.
After startup the database in nomount mode we need to alter database in mount mode using the below command in the SQL promt.
SQL>alter database mount;
We can check the oracle database stage using the below command .
Open stage:-- This is the last stage to startup a oracle database. Some tasks also occured during this stage.
1. In this stage oracle opens all datafiles and Redolog files(which is required for database recovery) .
2. Every one can access oracle database in this stage.
When oracle database is mounted mode we can alter database mode in open state using the below command.
SQL>alter database open;
In this lesson we have learned startup concept of oracle database. In the next lesson we will learn shutdown concept of oracle database.
Stay tune.
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