11g自动内存设置-整理自官方文档

The simplest way to manage instance memory is to allow the Oracle Database instance to automatically manage and tune it for you.

一种简单管理内存的方式是：让oracle自动为你管理和调优！

To do so (on most platforms), you set only a target memory size initialization parameter (

MEMORY_TARGET

) and optionally a
maximum memory size initialization parameter (

MEMORY_MAX_TARGET

).

多数平台上，你只需设置初始化参数MEMORY_TARGET，再随意（大于后者等于MEMORY_TARGET）设置初始化参数MEMORY_MAX_TARGET

The total memory that the instance uses remains relatively constant, based on the value of

MEMORY_TARGET

, and the instance automatically distributes memory between the system global area (SGA) and the instance program global area (instance PGA). As memory requirements change, the instance dynamically redistributes memory between the
SGA and instance PGA.

实例的总内存以MEMORY_TARGET设置的值为准（开机时oracle以MEMORY_TARGET参数值为准给instance分配内存！如果业务需要分配更大内存，oracle将自动扩展，但不能超过MEMORY_MAX_TARGET的值），实例根据需要自动分配内存给SGA和PGA

When automatic memory management is not enabled, you must size both the SGA and instance PGA manually.

当自动内存管理未启用时，你必须指定SGA和PGA的内存大小

Because the

MEMORY_TARGET

initialization parameter is dynamic, you can change

MEMORY_TARGET

at any time without restarting the database.

MEMORY_TARGET

是一个动态参数，可以再任何需要的时候进行调整而不必重启实例！

MEMORY_MAX_TARGET

, which is not dynamic, serves as an upper limit so that you cannot accidentally set

MEMORY_TARGET

too high, and so that enough memory is set aside for the database instance in case you do want to increase total instance memory in the future. Because certain SGA components either cannot easily shrink or must remain at a minimum
size, the instance also prevents you from setting

MEMORY_TARGET

too low.

MEMORY_MAX_TARGET是一个静态参数，作为一个上限值（限制

MEMORY_TARGET

参数），你不能将

MEMORY_TARGET

设置的过高，并且要保留足够的内存来满足在以后实例的扩张。但是实例总是不允许你将

MEMORY_TARGET参数设置的过低，因为SGA的组件大小有最小值限定，还有些组件是很难缩小的！

If you create your database with Database Configuration Assistant (DBCA) and choose the basic installation option, automatic memory management is enabled. If you choose advanced installation, Database Configuration Assistant (DBCA) enables you to select
automatic memory management.

如果你用DBCA创建数据库并且选择基本安装选项，自动内存默认是启用的！假如你是高级安装你也可以选择启用自动内存管理！

开启自动内存管理的步骤：

1：Start SQL*Plus and connect to the database as

SYSDBA

.

以sys用户登录

2：Calculate the minimum value for

MEMORY_TARGET

as follows:

计算

MEMORY_TARGET

的最小值！

a：Determine the current sizes of

SGA_TARGET

and

PGA_AGGREGATE_TARGET

by entering the following SQL*Plus command:

确定

SGA_TARGET

，

PGA_AGGREGATE_TARGET

参数的大小：

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
pga_aggregate_target           big integer 90M
sga_target                     big integer 272M

b：Run the following query to determine the maximum instance PGA allocated since the database was started:Run the following query to determine the maximum instance PGA allocated since the database was started:

确定从数据库启动以来实例分配给PGAde 的最大值：
select value/1024/1024||'m' from v$pgastat where name='maximum PGA allocated';

c：Compute the maximum value between the query result from step 2b and

PGA_AGGREGATE_TARGET

. Add

SGA_TARGET

to this value.

计算memory_target 最大值

memory_target = sga_target + max(pga_aggregate_target, maximum PGA allocated)

For example, if

SGA_TARGET

is 272M and

PGA_AGGREGATE_TARGET

is 90M as shown above, and if the maximum PGA allocated is determined to be 120M, then

MEMORY_TARGET

should be at least 392M (272M + 120M).

例如，如果

SGA_TARGET

is 272M，

PGA_AGGREGATE_TARGET

is 90M，maximum PGA allocated is 120M，那么

MEMORY_TARGET

的最小值为：392M (272M + 120M)。

这只是他的最小值！你也可以将值设置的更大，前提是有足够的物理内存！

3：For the

MEMORY_MAX_TARGET

initialization parameter, decide on a maximum amount of memory that you would want to allocate to the database for the foreseeable future. That is, determine the maximum value for the sum of the SGA and instance PGA
sizes. This number can be larger than or the same as the

MEMORY_TARGET

value that you chose in the previous step.

MEMORY_MAX_TARGET

这个参数的设置要大于或者等于

MEMORY_TARGET

参数的值。根据网上的一些经验之谈

MEMORY_MAX_TARGET

= OS_MEMORY*80%这参数的值没有固定公式可参考！要根据实际情况来确定！！

修改参数的脚本：

ALTER SYSTEM SET MEMORY_MAX_TARGET = nM SCOPE = SPFILE;

如果修改了该参数MEMORY_MAX_TARGET 需重启实例！

The dynamic performance view

V$MEMORY_DYNAMIC_COMPONENTS

shows the current sizes of all dynamically tuned memory components, including the total sizes of the SGA and instance PGA.

动态视图

V$MEMORY_DYNAMIC_COMPONENTS

显示了当前动态内存组件的大小。包括SGA,PGA的总大小！

The view

V$MEMORY_TARGET_ADVICE

provides tuning advice for the

MEMORY_TARGET

initialization parameter.

SQL>  select * from v$memory_target_advice order by memory_size;

MEMORY_SIZE MEMORY_SIZE_FACTOR ESTD_DB_TIME ESTD_DB_TIME_FACTOR    VERSION
----------- ------------------ ------------ ------------------- ----------
180                 .5          458               1.344          0
270                .75          367              1.0761          0
360                  1          341                   1          0
450               1.25          335               .9817          0
540                1.5          335               .9817          0
630               1.75          335               .9817          0
720                  2          335               .9817          0

The row with the

MEMORY_SIZE_FACTOR

of 1 shows the current size of memory, as set by the

MEMORY_TARGET

initialization parameter, and the amount of DB time required to complete the current workload. In previous and subsequent rows, the results show several alternative

MEMORY_TARGET

sizes. For each alternative size, the database shows the size factor (the multiple of the current size), and the estimated DB time to complete the current workload if the

MEMORY_TARGET

parameter were changed to the alternative size. Notice that for a total memory size smaller than the current

MEMORY_TARGET

size, estimated DB time increases. Notice also that in this example, there is nothing to be gained by increasing total memory size beyond 450MB. However, this situation might change if a complete workload has not yet been run.