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Oracle® Database Reference
11g Release 2 (11.2)

Part Number E17110-04
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Uses of Initialization Parameters

Initialization parameters fall into various functional groups. For example, parameters perform the following functions:

Database administrators can use initialization parameters to:

Many initialization parameters can be fine-tuned to improve database performance. Other parameters should never be altered or should be altered only under the supervision of Oracle Support Services.

All initialization parameters are optional. Oracle has a default value for each parameter. This value may be operating system-dependent, depending on the parameter.

Types of Initialization Parameters

The Oracle database server has the following types of initialization parameters:

Derived Parameters

Some initialization parameters are derived, meaning that their values are calculated from the values of other parameters. Normally, you should not alter values for derived parameters, but if you do, then the value you specify will override the calculated value.

For example, the default value of the SESSIONS parameter is derived from the value of the PROCESSES parameter. If the value of PROCESSES changes, then the default value of SESSIONS changes as well, unless you override it with a specified value.

Operating System-Dependent Parameters

The valid values or value ranges of some initialization parameters depend upon the host operating system. For example, the parameter DB_BLOCK_BUFFERS indicates the number of data buffers in main memory, and its maximum value depends on the operating system. The size of those buffers, set by DB_BLOCK_SIZE, has an operating system-dependent default value.

See Also:

Your operating system-specific Oracle documentation for more information on operating system-dependent Oracle parameters and operating system parameters

Variable Parameters

The variable initialization parameters offer the most potential for improving system performance. Some variable parameters set capacity limits but do not affect performance. For example, when the value of OPEN_CURSORS is 10, a user process attempting to open its eleventh cursor receives an error. Other variable parameters affect performance but do not impose absolute limits. For example, reducing the value of DB_BLOCK_BUFFERS does not prevent work even though it may slow down performance.

Increasing the values of variable parameters may improve your system's performance, but increasing most parameters also increases the system global area (SGA) size. A larger SGA can improve database performance up to a point. In virtual memory operating systems, an SGA that is too large can degrade performance if it is swapped in and out of memory. Operating system parameters that control virtual memory working areas should be set with the SGA size in mind. The operating system configuration can also limit the maximum size of the SGA.