Oracle自動內存管理AMM
AMM(Automatic Memory Management)自動內存管理，分配一整塊內存區域，Oracle數據庫自動分配管理SGA和PGA的內存。具體通過設置兩個參數MEMORY_MAX_TARGET和MEMORY_TARGET達到需求效果。
1.查看當前SGA_TARGET和PGA_AGGREGATE_TARGET參數。
SYS@oradb> show parameter target;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
archive_lag_target integer 0
db_flashback_retention_target integer 1440
fast_start_io_target integer 0
fast_start_mttr_target integer 0
memory_max_target big integer 0
memory_target big integer 0
parallel_servers_target integer 256
pga_aggregate_target big integer 2951M
sga_target big integer 4G
2.修改相關參數，把sga和pga參數改為0
alter system set memory_max_target=16384m scope=spfile;
alter system set memory_target=16384m scope=spfile;
alter system set sga_target=0 scope=spfile;
alter system set sga_max_size=0 scope=spfile;
alter system set pga_aggregate_target=0 scope=spfile;
3.重啟數據庫實例:
SQL>shutdown immediate;
SQL>startup;
SYS@oradb> show parameter target;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
archive_lag_target integer 0
db_flashback_retention_target integer 1440
fast_start_io_target integer 0
fast_start_mttr_target integer 0
memory_max_target big integer 16G
memory_target big integer 16G
parallel_servers_target integer 256
pga_aggregate_target big integer 0
sga_target big integer 0
至此，數據庫切換至AMM內存管理。
4.監控和優化AMM的內存
動態性能視圖V$MEMORY_DYNAMIC_COMPONENTS顯示所有動態內存組件的當前大小。
動態性能視圖V$MEMORY_RESIZE_OPS會有一個circular history buffer，查看最近16G內存的請求情況。
動態性能視圖V$MEMORY_TARGET_ADVICE,會給與一個內存優化建議。
SYS@oradb> SELECT * FROM v$memory_target_advice ORDER BY memory_size;
MEMORY_SIZE MEMORY_SIZE_FACTOR ESTD_DB_TIME ESTD_DB_TIME_FACTOR VERSION
----------- ------------------ ------------ ------------------- ----------
4096 .25 487 1 0
8192 .5 487 1 0
10240 .625 487 1 0
12288 .75 487 1 0
14336 .875 487 1 0
16384 1 487 1 0
18432 1.125 487 1 0
20480 1.25 487 1 0
22528 1.375 487 1 0
24576 1.5 487 1 0
26624 1.625 487 1 0
28672 1.75 487 1 0
30720 1.875 487 1 0
32768 2 487 1 0
備注:Automatic Shared Memory Management (ASMM) was introduced in 10g. You enable the automatic shared memory management feature by setting the SGA_TARGET parameter to a non-zero value.
關於SGA_TARGET 動態內存建議視圖如下:
SYS@oradb> select * from v$sga_target_advice;
SGA_SIZE SGA_SIZE_FACTOR ESTD_DB_TIME ESTD_DB_TIME_FACTOR ESTD_PHYSICAL_READS
---------- --------------- ------------ ------------------- -------------------
2457 .25 488 1 42221
3685 .3749 488 1 42221
4914 .5 488 1 42221
6142 .6249 488 1 42221
7371 .75 488 1 42221
8599 .8749 488 1 42221
9828 1 488 1 42221
11056 1.1249 488 1 42221
12285 1.25 488 1 42221
13513 1.3749 488 1 42221
14742 1.5 488 1 42221
15970 1.6249 488 1 42221
17199 1.75 488 1 42221
18427 1.8749 488 1 42221
19656 2 488 1 42221