OCP-1Z0-052-V9.02-177题

177.Which two statements are true regarding the SGA_TARGET initialization parameter? (Choose two.)
A. It can be increased up to the value of the SGA_MAX_SIZE parameter.
B. Increasing the value of the SGA_TARGET parameter distributes the increased memory among all the autotuned components.
C. Reducing the value of the SGA_TARGET parameter deallocates memory from both autotuned and manually sized components.
D. Increasing the value of SGA_TARGET up to the value of SGA_MAX_SIZE disables the automatic shared memory management feature.
Answer: AB
答案解析：
参考：http://docs.oracle.com/cd/E11882_01/server.112/e25494/memory.htm#ADMIN11215

About Automatic Shared Memory Management

Automatic Shared Memory Management simplifies SGA memory management. You specify the total amount of SGA memory available to an instance using the

SGA_TARGET

initialization parameter and Oracle
Database automatically distributes this memory among the various SGA components to ensure the most effective memory utilization.

When automatic shared memory management is enabled, the sizes of the different SGA components are flexible and can adapt to the needs of a workload without requiring any additional configuration. The database automatically distributes the available memory among
the various components as required, allowing the system to maximize the use of all available SGA memory.

If you are using a server parameter file (

SPFILE

), the database remembers the sizes of the automatically tuned SGA components across instance shutdowns. As a result, the database instance does not need to learn the characteristics
of the workload again each time the instance is started. The instance can begin with information from the previous instance and continue evaluating workload where it left off at the last shutdown.




Dynamic Modification of SGA_TARGET

The

SGA_TARGET

parameter can be dynamically increased up to the value specified for the

SGA_MAX_SIZE

parameter,
and it can also be reduced. If you reduce the value of

SGA_TARGET

, the system identifies one or more automatically tuned components for which to release memory. You
can reduce

SGA_TARGET

until one or more automatically tuned components reach their minimum size. Oracle Database determines the minimum allowable value for

SGA_TARGET

taking
into account several factors, including values set for the automatically sized components, manually sized components that use

SGA_TARGET

space, and number of CPUs.

The change in the amount of physical memory consumed when

SGA_TARGET

is modified depends on the operating system. On some UNIX platforms that do not support dynamic shared memory, the physical memory in use by the SGA is
equal to the value of the

SGA_MAX_SIZE

parameter. On such platforms, there is no real benefit in setting

SGA_TARGET

to a value smaller than

SGA_MAX_SIZE

.
Therefore, setting

SGA_MAX_SIZE

on those platforms is not recommended.

On other platforms, such as Solaris and Windows, the physical memory consumed by the SGA is equal to the value of

SGA_TARGET

.

For example, suppose you have an environment with the following configuration:

SGA_MAX_SIZE

= 1024M

SGA_TARGET

= 512M

DB_8K_CACHE_SIZE

= 128M

In this example, the value of

SGA_TARGET

can be resized up to 1024M and can also be reduced until one or more of the automatically sized components reaches its minimum size. The exact value depends on environmental factors
such as the number of CPUs on the system. However, the value of

DB_8K_CACHE_SIZE

remains fixed at all times at 128M