Oracle Essentials: Oracle9i, Oracle8i and Oracle8, Second Edition

Starting Up the Database

Starting a database is quite simple—on Windows NT you simply start the Oracle services, and on Unix you issue the STARTUP command from Server Manager or SQL*Plus (in Oracle8i). While starting a database appears to be a single action, it involves an instance and a database and occurs in several distinct phases. When you start a database, the following actions are automatically executed:

1. Starting the instance. Oracle reads the instance initialization parameters from the SPFILE or INIT.ORA file on the server. Oracle then allocates memory for the System Global Area and starts the background processes of the instance. At this point, none of the physical files in the database have been opened, and the instance is in the NOMOUNT state.

   There are problems that can prevent an instance from starting. For example, there may be errors in the initialization file, or the operating system may not be able to allocate the requested amount of shared memory for the SGA. You also need the special privilege SYSOPER or SYSDBA, granted through either the operating system or a password file, to start an instance.

2. Mounting the database. The instance opens the database’s control files. The initialization parameter CONTROL_FILES tells the instance where to find these control files. At this point only the control files are open. This is called the MOUNT state, and at this time, the database is accessible only to the database administrator. In this state, the DBA can perform only ...