Database operating modes oracle startup shutdown sequence

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oracle database operating modes, startup, and shutdown sequence: a comprehensive guide

this tutorial will delve deep into oracle database operating modes, the startup and shutdown sequences, and provide practical code examples to illustrate these concepts. understanding these core aspects is crucial for any oracle dba or developer aiming to manage and maintain oracle databases effectively.

*i. oracle database operating modes*

an oracle database operates in one of several modes, determining its accessibility and functionality. these modes are typically managed during startup and shutdown. the primary operating modes are:

*`startup` (no mount):* this mode is the first step in starting the database.
*what happens:* the instance is started. this involves:
allocating system global area (sga) based on initialization parameters.
starting background processes (e.g., pmon, smon, dbwn, lgwr, ckpt).
reading the parameter file (init.ora or spfile.ora)
*what's *not happening:**
control files are not opened.
data files are not opened.
redo log files are not opened.
the database is not accessible to users (except with `as sysdba`).
*use cases:*
creating a new database.
recovering from a severe loss of control files.
performing some maintenance tasks that don't require accessing the database.

*`mount`:* this mode prepares the database for opening by associating the instance with the control files.
*what happens:*
the control files, specified in the initialization parameter `control_files`, are opened.
the database name and other control file information are read.
the database state is validated.
*what's *not happening:**
data files are not opened.
redo log files are not opened.
the database is not accessible ...

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Database operating modes
Oracle startup
Oracle shutdown
database initialization
database instance
Oracle instance management
database configuration
Oracle commands
database recovery
database states
Oracle server processes
database control
Oracle environment variables
database maintenance
Oracle performance tuning