10g在视图v$sga_dynamic_components中我们注意到多了一个component：ASM Buffer Cache，并且在instance_type=asm的实例中该参数有值，也就是说该参数是为asm实例所使用，它是用来做什么，在doc中搜了一下没找到，我猜测应该和db_cache_size的作用差不多，估计是用来cache disk header信息的。

SQL> select component,current_size from v$sga_dynamic_components;

COMPONENT CURRENT_SIZE

------------------------------ ------------

shared pool 41943040

large pool 12582912

java pool 0

streams pool 0

DEFAULT buffer cache 0

KEEP buffer cache 0

RECYCLE buffer cache 0

DEFAULT 2K buffer cache 0

DEFAULT 4K buffer cache 0

DEFAULT 8K buffer cache 0

DEFAULT 16K buffer cache 0

COMPONENT CURRENT_SIZE

------------------------------ ------------

DEFAULT 32K buffer cache 0

ASM Buffer Cache 25165824

13 rows selected.

SQL> alter system set sga_target=80m;

alter system set sga_target=80m

*

ERROR at line 1:

ORA-15021: parameter "sga_target" is not valid in asm instance

--无意中发现sga_target不适合asm实例类型

SQL> show parameter instance_type

NAME TYPE VALUE

---------------------------------------------------------

instance_type string asm

SQL>

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