Important Initialization Parameters With Performance Impact in 10g

COMPATIBLE :=
Specifies the release with which the Oracle server must maintain compatibility. It lets you take advantage of the maintenance improvements of a new release immediately in your production systems without testing the new functionality
in your environment. If your application was designed for a specific release of Oracle, and you are actually installing a later release, then you might want to set this parameter to the version of the previous release.

DB_BLOCK_SIZE :=
Sets the size of the Oracle database blocks stored in the
database files and cached in the SGA. The range of values depends on the operating system, but it is typically 8192 for transaction processing systems and higher values for database warehouse systems.

SGA_TARGET :=
Specifies the total size of all SGA components. If SGA_TARGET
is specified, then the buffer cache (DB_CACHE_SIZE), Java pool (JAVA_POOL_SIZE), large pool (LARGE_POOL_SIZE), and shared pool (SHARED_POOL_SIZE) memory pools are
automatically sized.

PGA_AGGREGATE_TARGET :=
Specifies the target aggregate PGA memory available to all
server processes attached to the instance.

PROCESSES :=
Sets the maximum number of processes that can be started by
that instance. This is the most important primary parameter to set, because many other parameter values are deduced from this.

SESSIONS :=
This is set by default from the value of processes. However, if
you are using the shared server, then the deduced value is likely to be insufficient.

UNDO_MANAGEMENT:=
Specifies which undo space management mode the system
should use. AUTO mode is recommended.

UNDO_TABLESPACE :=
Specifies the undo tablespace to be used when an instance
starts up.