Manually Managed SGA Components (76)

There are a few SGA components whose sizes are not automatically adjusted. The
administrator needs to specify the sizes of these components explicitly, if needed by
the application. Such components are:
■ Keep/Recycle buffer caches (controlled by DB_KEEP_CACHE_SIZE and DB_RECYCLE_CACHE_SIZE)
■ Additional buffer caches for non-standard block sizes (controlled by DB_nK_
CACHE_SIZE, n = {2, 4, 8, 16, 32})
The sizes of these components is determined by the administrator-defined value of
their corresponding parameters. These values can, of course, be changed any time
either using Enterprise Manager or from the command line with an ALTER SYSTEM
statement.
The memory consumed by manually sized components reduces the amount of
memory available for automatic adjustment. For example, in the following
configuration:
SGA_TARGET = 256M
DB_8K_CACHE_SIZE = 32M
The instance has only 224 MB (256 - 32) remaining to be distributed among the
automatically sized components.

sga组件手动管理
DB_KEEP_CACHE_SIZE ：Keep buffer caches
DB_RECYCLE_CACHE_SIZE ： Recycle buffer caches
DB_nK_CACHE_SIZE n为非标准块的大小
这些参数需要手工指定 ， 也可以用alter system语句实时更改
手工调整的组件 + 自动调整的组件 = SGA_TARGET

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