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About Instance Startup

Whcn you start thc Oracle instance, you typically start it such that the State of the database is OPEN and ready for user connections. However, there arc situations in which you may want to start the instance with the database in the MOUNTED State, but not open. An instance can also be startcd without the database cither mounted or open. Thus, there are thrce stages to starting an instance:

1.    You start the instance using one of the following methods:

■Using the SQL*Plus STARTUP command. See "Shutting Down and Starting Up Using SQL*Plus" on pagc 5-8.

■On Microsoft Windows, using thc Scrviccs program in Control Panel to start thc Oracle Database scrviccs. See "Shutting Down and Starting Up Using thc Windows Scrviccs Program" on page 5-9.

The instance reads the initialization parametcr file, allocatcs SGA mcmory, and starts the background processes.

2.    If you mount the database, then the Oracle instance opens the control file for the database, but does not open the data files. The database is now considered to be in the MOUNT State. This State enables you to perform ccrtain administrative functions that cannot be performcd when othcr users are accessing the database. An cxamplc of such a function is cnabling or disabling the archiving of online redo

log files. See "About Archived Redo Log Files" on page 6-4 for information about online redo log file archiving.

3.    If you open the database, then, after reading the parameter file and control file, the online redo log files and data files for the database are also opened. The State of

thc database is now OPEN and user acccss to the data is availablc.

The default startup modę for the database (OPEN) completes the three stages in sequence. Unless you explicitly specify otherwise, the instance is started, the database is mounted, and then the database is opened.