v$sgainfo中Free SGA Memory Available的各种情况解释

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标题:v$sgainfo中Free SGA Memory Available的各种情况解释

作者:惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

今天网友问到了v$sgainfo中的Free SGA Memory Available的一些情况,开始我也比较迷糊,为什么会出现Free SGA Memory Available的值不为0,通过查询一些试验和测试,对这个问题进行了有力的说明
数据库版本10G

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Prod
PL/SQL Release 10.2.0.4.0 - Production
CORE    10.2.0.4.0      Production
TNS for Linux: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production

当前SGA各组件信息

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

NAME                             BYTES/1024/1024
-------------------------------- ---------------
Fixed SGA Size                        1.20853043
Redo Buffers                           6.7890625
Buffer Cache Size                            192
Shared Pool Size                              88
Large Pool Size                                4
Java Pool Size                                 4
Streams Pool Size                              8
Granule Size                                   4
Maximum SGA Size                             304
Startup overhead in Shared Pool               36
Free SGA Memory Available                      0

11 rows selected.

sga配置

SQL> show parameter sga;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ---------------
lock_sga                             boolean     FALSE
pre_page_sga                         boolean     FALSE
sga_max_size                         big integer 304M
sga_target                           big integer 304M

在10g中,当采用asmm管理时,如果sga_max_size=sga_target,则Free SGA Memory Available为0

修改sga_target

SQL> alter system set sga_target=290M;

System altered.

再次查询v$sgainfo

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

NAME                             BYTES/1024/1024
-------------------------------- ---------------
Fixed SGA Size                        1.20853043
Redo Buffers                           6.7890625
Buffer Cache Size                            180
Shared Pool Size                              88
Large Pool Size                                4
Java Pool Size                                 4
Streams Pool Size                              8
Granule Size                                   4
Maximum SGA Size                             304
Startup overhead in Shared Pool               36
Free SGA Memory Available                     12

11 rows selected.

再次查看sga_target值

SQL> show parameter sga;

NAME                                 TYPE        VALUE
------------------------------------ ----------- --------------
lock_sga                             boolean     FALSE
pre_page_sga                         boolean     FALSE
sga_max_size                         big integer 304M
sga_target                           big integer 292M

在10g中,当采用asmm管理时,如果sga_max_size>sga_target,则Free SGA Memory Available为sga_max_size-sga_target

找出sga_target修改为292M而不是290M原因

SQL> select component, granule_size from v$sga_dynamic_components;

COMPONENT                                                        GRANULE_SIZE
---------------------------------------------------------------- ------------
shared pool                                                           4194304
large pool                                                            4194304
java pool                                                             4194304
streams pool                                                          4194304
DEFAULT buffer cache                                                  4194304
KEEP buffer cache                                                     4194304
RECYCLE buffer cache                                                  4194304
DEFAULT 2K buffer cache                                               4194304
DEFAULT 4K buffer cache                                               4194304
DEFAULT 8K buffer cache                                               4194304
DEFAULT 16K buffer cache                                              4194304
DEFAULT 32K buffer cache                                              4194304
ASM Buffer Cache                                                      4194304

13 rows selected.

SQL> select 4194304/1024/1024 from dual;

4194304/1024/1024
-----------------
                4

SQL> select 292/4 from dual;

     292/4
----------
        73

因为sga的内存分配是按照GRANULE为单位进行的,而在该库中sga对应组件的GRANULE为4M,所以我们修改的290M的最近的GRANULE整数倍为292M

sga_target为0的情况

SQL> show parameter sga_target;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ----------
sga_target                           big integer 0

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

NAME                             BYTES/1024/1024
-------------------------------- ---------------
Fixed SGA Size                        1.20846176
Redo Buffers                           6.7890625
Buffer Cache Size                            180
Shared Pool Size                              88
Large Pool Size                                4
Java Pool Size                                 4
Streams Pool Size                              8
Granule Size                                   4
Maximum SGA Size                             292
Startup overhead in Shared Pool               36
Free SGA Memory Available                      0

11 rows selected.

在10g中,如果不采用asmm内存管理模式,Free SGA Memory Available为0

11g数据库版本

SQL> select * from v$version;

BANNER
-----------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - Production
PL/SQL Release 11.2.0.3.0 - Production
CORE    11.2.0.3.0      Production
TNS for Linux: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production

查询v$sgainfo信息

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

NAME                             BYTES/1024/1024
-------------------------------- ---------------
Fixed SGA Size                        1.28236008
Redo Buffers                          6.03515625
Buffer Cache Size                             20
Shared Pool Size                             116
Large Pool Size                                4
Java Pool Size                                 4
Streams Pool Size                              8
Shared IO Pool Size                            0
Granule Size                                   4
Maximum SGA Size                      299.320313
Startup overhead in Shared Pool       52.2684898
Free SGA Memory Available                    140

oracle内存相关参数设置

SQL> show parameter memory;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------
hi_shared_memory_address             integer     0
memory_max_target                    big integer 300M
memory_target                        big integer 300M
shared_memory_address                integer     0

SQL> show parameter pga;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------
pga_aggregate_target                 big integer 0

数据库动态组件内存分配

SQL> select COMPONENT,CURRENT_SIZE/1024/1024 CURRENT_SIZE from V$MEMORY_DYNAMIC_COMPONENTS;

COMPONENT                                                        CURRENT_SIZE
---------------------------------------------------------------- ------------
shared pool                                                               116
large pool                                                                  4
java pool                                                                   4
streams pool                                                                8
SGA Target                                                                160
DEFAULT buffer cache                                                       20
KEEP buffer cache                                                           0
RECYCLE buffer cache                                                        0
DEFAULT 2K buffer cache                                                     0
DEFAULT 4K buffer cache                                                     0
DEFAULT 8K buffer cache                                                     0
DEFAULT 16K buffer cache                                                    0
DEFAULT 32K buffer cache                                                    0
Shared IO Pool                                                              0
PGA Target                                                                140
ASM Buffer Cache                                                            0

16 rows selected.

初步怀疑:在11g的amm内存管理模式下Free SGA Memory Available和PGA Target相等

尝试修改pga_aggregate_target值

SQL> alter system set pga_aggregate_target=150M;

System altered.

再次查询v$sgainfo

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

NAME                             BYTES/1024/1024
-------------------------------- ---------------
Fixed SGA Size                        1.28236008
Redo Buffers                          6.03515625
Buffer Cache Size                              8
Shared Pool Size                             116
Large Pool Size                                4
Java Pool Size                                 4
Streams Pool Size                              8
Shared IO Pool Size                            0
Granule Size                                   4
Maximum SGA Size                      299.320313
Startup overhead in Shared Pool       52.2684898
Free SGA Memory Available                    152

查询动态组件内存分布

SQL> select COMPONENT,CURRENT_SIZE/1024/1024 CURRENT_SIZE from V$MEMORY_DYNAMIC_COMPONENTS;

COMPONENT                                                        CURRENT_SIZE
---------------------------------------------------------------- ------------
shared pool                                                               116
large pool                                                                  4
java pool                                                                   4
streams pool                                                                8
SGA Target                                                                148
DEFAULT buffer cache                                                        8
KEEP buffer cache                                                           0
RECYCLE buffer cache                                                        0
DEFAULT 2K buffer cache                                                     0
DEFAULT 4K buffer cache                                                     0
DEFAULT 8K buffer cache                                                     0
DEFAULT 16K buffer cache                                                    0
DEFAULT 32K buffer cache                                                    0
Shared IO Pool                                                              0
PGA Target                                                                152
ASM Buffer Cache                                                            0

16 rows selected.

进一步证明:在11g的amm内存管理模式下Free SGA Memory Available和PGA Target相等

设置pga_aggregate_target为150M,PGA Target为152M原因分析

SQL> select COMPONENT,GRANULE_SIZE from V$MEMORY_DYNAMIC_COMPONENTS;

COMPONENT                                                        GRANULE_SIZE
---------------------------------------------------------------- ------------
shared pool                                                           4194304
large pool                                                            4194304
java pool                                                             4194304
streams pool                                                          4194304
SGA Target                                                            4194304
DEFAULT buffer cache                                                  4194304
KEEP buffer cache                                                     4194304
RECYCLE buffer cache                                                  4194304
DEFAULT 2K buffer cache                                               4194304
DEFAULT 4K buffer cache                                               4194304
DEFAULT 8K buffer cache                                               4194304
DEFAULT 16K buffer cache                                              4194304
DEFAULT 32K buffer cache                                              4194304
Shared IO Pool                                                        4194304
PGA Target                                                            4194304
ASM Buffer Cache                                                      4194304

16 rows selected.

原理同上述10g中的sga_target分析,不再重复,主要就是:150M不能被4M整除,所以取最近的152M

整体总结
1.如果不采用asmm和amm,Free SGA Memory Available为0
2.如果采用asmm,当sga_max_size=sga_target,则Free SGA Memory Available为0
3.如果采用asmm,当sga_max_size>sga_target,则Free SGA Memory Available为sga_max_size-sga_target
4.如果采用amm,Free SGA Memory Available和PGA Target相等

此条目发表在 Oracle 分类目录。将固定链接加入收藏夹。

v$sgainfo中Free SGA Memory Available的各种情况解释》有 1 条评论

  1. 兜兜 说:

    谢谢飞总的分享!
    从本人学习到2点,算自己的读文收获,也分享给作者。
    1、10g sga内存与11g pga内存分配方式均是:由v$sga_dynamic_components中granule_size为单位,按此单位进行倍增。并此单位为动态(此单位根据使用内存情况会所变化)。
    2、采用asmm时,Free SGA Memory Available=(sga_max_size-sga_target)》=0
    采用smm时,Free SGA Memory Available=PGA Target

      [引用]  [回复]

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