TRAINING (ORA-9) - Different Stages while Opening an Oracle Database

Different Stages while Opening an Oracle Database

When Oracle software binaries tries to open an Oracle database, it passes through three different stages:

1.) Startup (nomount)
2.) Mount
3.) Open




High level requirements for opening an Oracle database:
> All control files must be present and synchronized
> All online data files must be present and synchronized
> At least one member of each redo log group must be present

Stage-1: Starting Up a Database (NOMOUNT)

Command:
SQL> startup nomount



Stage-2: Starting Up a Database (MOUNT)

Command:
SQL> startup mount
or
SQL> alter database mount



Stage-3: Starting Up a Database (OPEN)

Command:
SQL> startup
or
SQL> alter database open




High level requirements for keep an Oracle database running
Once open, the instance could fail with:
Loss of any control file
Loss of a data file belonging to the system or undo tablespaces
Loss of an entire redo log group. As long as at least one member of the group is available, the instance remains open.