Oracle分配内存的基本单位:Granule(粒度)

在9i后,SGA的内部组件大小可以动态调整,也可以由数据库自动管理,在设置内存大小的时候,分配的基本单位是粒度(granule

  • granule是一段连续的虚拟内存,大小区域决SGA_MAX_SIZE大小
  • SGA_MAX_SIZE小于128MGranule4M,否则Granule16M
  • 每个内存组件分配大小必须为Granule的整数倍
  • 整个SGA最小不小于3Granule大小
  • 查看granule大小:v$sgainfo
  • 如下,因为sga_max_size大小大于128M,所以granule大小为16M

SQL> select name,bytes/1024/1024 MB,resizeable from v$sgainfo;

 

NAME                                     MB RES

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

Fixed SGA Size                   2.14937592 No

Redo Buffers                       6.765625 No

Buffer Cache Size                       608 Yes

Shared Pool Size                        272 Yes

Large Pool Size                          32 Yes

Java Pool Size                           16 Yes

Streams Pool Size                         0 Yes

Shared IO Pool Size                       0 Yes

Granule Size                             16 No

Maximum SGA Size                 1576.91797 No

Startup overhead in Shared Pool   189.55072 No

Free SGA Memory Available               640

 

12 rows selected.

 

SQL> show parameter sga_max_size

 

NAME                                 TYPE        VALUE

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

sga_max_size                         big integer 1584M

 

再看如下例子:

虽然设置shared_pool_size大小为10M,但是查看是确实16M,那是因为分配内存的基本单位是粒度granule.每个内存组件分配大小必须为granule的整数倍.

SQL> show parameter shared_p;

 

NAME                                 TYPE        VALUE

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

shared_pool_reserved_size            big integer 10066329

shared_pool_size                     big integer 0

 

SQL> alter system set shared_pool_size=10M;

 

System altered.

 

SQL> show parameter shared_p;

 

NAME                                 TYPE        VALUE

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

shared_pool_reserved_size            big integer 10066329

shared_pool_size                     big integer 16M

 

posted @ 2017-07-11 10:15  寻香径  阅读(797)  评论(0编辑  收藏  举报