Oracle自動內存管理的幾個小問題

1) 開啓了自動內存管理以後，若是有pool的值設置爲非0值會怎麼處理？

好比，設置了sga_target=10G，可是java_pool_size設置爲10m，這時，10m會做爲java pool的最少分配內存空間。

If these automatically tuned memory pools had been set to nonzero values, those values are used as minimum levels by Automatic Shared Memory Management. You would set minimum values if an application component needs a minimum amount of memory to function properly.

2) 關閉自動管理後，相關pool的值會被自動設置。

If you dynamically disable SGA_TARGET by setting its value to 0 at instance startup, Automatic Shared Memory Management will be disabled and the current auto-tuned sizes will be used for each memory pool.

sys@HUA>show parameter memory;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
hi_shared_memory_address             integer     0
memory_max_target                    big integer 0
memory_target                        big integer 0
shared_memory_address                integer     0
sys@HUA>show parameter sga

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
lock_sga                             boolean     FALSE
pre_page_sga                         boolean     FALSE
sga_max_size                         big integer 440M
sga_target                           big integer 440M
sys@HUA>alter system set sga_target=0;

System altered.

sys@HUA>show parameter pool;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
_shared_io_pool_size                 big integer 0
buffer_pool_keep                     string
buffer_pool_recycle                  string
global_context_pool_size             string
java_pool_size                       big integer 4M
large_pool_size                      big integer 8M
olap_page_pool_size                  big integer 0
shared_pool_reserved_size            big integer 7549747
shared_pool_size                     big integer 208M
streams_pool_size                    big integer 0
sys@HUA>alter system set sga_target=440;

System altered.

sys@HUA>show parameter pool;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
_shared_io_pool_size                 big integer 0
buffer_pool_keep                     string
buffer_pool_recycle                  string
global_context_pool_size             string
java_pool_size                       big integer 4M
large_pool_size                      big integer 8M
olap_page_pool_size                  big integer 0
shared_pool_reserved_size            big integer 7549747
shared_pool_size                     big integer 208M
streams_pool_size                    big integer 0
sys@HUA>alter system set java_pool_size=0;

System altered.

sys@HUA>alter system set large_pool_size=0;

System altered.

sys@HUA>alter system set shared_pool_size=0;

System altered.

sys@HUA>
sys@HUA>show parameter pool;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
_shared_io_pool_size                 big integer 0
buffer_pool_keep                     string
buffer_pool_recycle                  string
global_context_pool_size             string
java_pool_size                       big integer 0
large_pool_size                      big integer 0
olap_page_pool_size                  big integer 0
shared_pool_reserved_size            big integer 7549747
shared_pool_size                     big integer 0
streams_pool_size                    big integer 0
sys@HUA>
sys@HUA>
sys@HUA>alter system set sga_target=0;

System altered.

sys@HUA>show parameter pool;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
_shared_io_pool_size                 big integer 0
buffer_pool_keep                     string
buffer_pool_recycle                  string
global_context_pool_size             string
java_pool_size                       big integer 4M
large_pool_size                      big integer 8M
olap_page_pool_size                  big integer 0
shared_pool_reserved_size            big integer 7549747
shared_pool_size                     big integer 208M
streams_pool_size                    big integer 0

3) 是否有在SGA內的組件，可是卻不在自動內存管理以內的？

The following pools are manually sized components and are not affected by Automatic Shared Memory Management: * Log buffer * Other buffer caches (such as KEEP, RECYCLE, and other nondefault block size) * Fixed SGA and other internal allocations To manually size these memory pools, you must set the DB_KEEP_CACHE_SIZE, DB_RECYCLE_CACHE_SIZE, DB_nK_CACHE_SIZE, and LOG_BUFFER initialization parameters. The memory allocated to these pools is deducted from the total available for SGA_TARGET when Automatic Shared Memory Management computes the values of the automatically tuned memory pools.

4） 組件之間「挪借」內存空間，是按什麼單位進行？是一個一個字節來分配？

Memory for the shared pool, large pool, java pool, and buffer cache is allocated in units of granules. The granule size is 4MB if the SGA size is less than 1GB. If the SGA size is greater than 1GB, the granule size changes to 16MB. The granule size is calculated and fixed when the instance starts up. The size does not change during the lifetime of the instance.

The granule size that is currently being used for SGA can be viewed in the view V$SGA_DYNAMIC_COMPONENTS. The same granule size is used for all dynamic components in the SGA.

5） 若是使用了自動內存管理，每一個pool的值都設置爲0了，那如何查看當前每一個pool的當前值？

V$MEMORY_DYNAMIC_COMPONENTS displays information about the current sizes of all dynamically tuned memory components, including the total sizes of the SGA and instance PGA.