SGA_MAX_SIZE:  static parameter

To use ASMM，need two parameters:

1.SGA_TARGET  not null or zero;

2.STATISTICS_LEVEL = TYPICAL ( or ALL)

when u use ASMM,the sga is auto management 

example: 

SGA_MAX_SIZE : 12G

SGA_TARGET   : 10G

2G (12G-10G) memory is not use at all.

parameters:

LOG_BUFFER=1G;( the parameter is only for the example  and assume there is no fixed sga ,actually it is impossible)

other parameters  = 0

steps:

1.

ALTER SYSTEM SET DB_CACHE_SIZE=8G； — succeed!

2.

ALTER SYSTEM SET DB_CACHE_SIZE=2G; — succeed!

3.

ALTER SYSTEM SET SHARED_POOL_SIZE=6G; — succeed!

4.

ALTER SYSTEM SET SHARED_POOL_SIZE=1G; — succeed!

5.

ALTER SYSTEM SET DB_CACHE_SIZE=4G; — failed !

SHOW PARAMETER SHARED_POOL_SIZE

it will display: 1G

u can not manually set the DB_CACHE_SIZE to 4G，unless u disable the ASMM.

—————————————

SHARED_POOL_SIZE,

LARGE_POOL_SIZE,

JAVA_POOL_SIZE,

STREAMS_POOL_SIZE 

will the same result.

—————————————

DB_KEEP_CACHE_SIZE,

DB_RECYCLE_CACHE_SIZE,

nK BLOCK CACHE SIZE

are not the same result.

If u use DB_KEEP_CACHE_SIZE replaces  SHARED_POOL_SIZE,

step 5 will succeed!

—————————————

doc says:

DB_KEEP_CACHE_SIZE is manual component ,so when it shrink,the auto components can use the memory immediate.

but:

DB_CACHE_SIZE is auto too! when shrink this parameter,query v$sgainfo and

v$sga_dynamic_comonents ,it size does not change, but the memory can be used immediate. 

see :  step 1,2,3

so i guess parameter “cache”  is different from  “pool”.

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