Oracle Database 10g Documentation Library

Uses of Initialization Parameters

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

Set limits for the entire database
Set user or process limits
Set limits on database resources
Affect performance (these are called variable parameters)

Variable parameters are of particular interest to database administrators, because these parameters are used primarily to improve database performance.

Database administrators can use initialization parameters to:

Optimize performance by adjusting memory structures, such as the number of database buffers in memory
Set database-wide defaults, such as the amount of space initially allocated for a context area when it is created
Set database limits, such as the maximum number of database users
Specify names of files or directories required by the database

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
Operating System-Dependent Parameters
Variable Parameters (these can be dynamic parameters or any of the preceding ones)

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.

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.