从数据库参数和系统内核参数解决ORA-00845错误

今天数据库启动时出现了ORA-00845: MEMORY_TARGET not supported on this system

官方错误原因描述：

ORA-00845: MEMORY_TARGET not supported on this system
Cause: The MEMORY_TARGET parameter was not supported on this operating system or /dev/shm was not sized correctly on Linux.
Action: Refer to documentation for a list of supported operating systems. Or, size /dev/shm to be at least the SGA_MAX_SIZE on each Oracle instance running on the system.

官方解决版本如下：
Starting with Oracle Database 11g, the Automatic Memory Management feature requires more shared memory (/dev/shm)and file descriptors. The size of the shared memory（shm） should be at least the greater of MEMORY_MAX_TARGET and MEMORY_TARGET for each Oracle instance on the computer. If MEMORY_MAX_TARGET or MEMORY_TARGET is set to a non zero value, and an incorrect size is assigned to the shared memory, it will result in an ORA-00845 error at startup.

大概的意思是：这个问题是由于设置SGA或MEMORY_MAX_TARGET 的大小超过了操作系统/dev/shm的大小，Oracle在metalink的文档：Doc ID:Note:460506.1中进行了说明。

数据库安装前配置时，在文件/etc/sysctl.conf 中修改了如下的内核参数

# Controls the maximum shared segment size, in bytes
kernel.shmmax = 536870912

Linux中系统内核正在使用的shared memory大小查看，通过/etc/sysctl.conf 的注释知道该参数默认以byte为单位
 

cat /proc/sys/kernel/shmmax
536870912

以M为单位计算共享内存大小
 

echo  536870912/1024/1024 | bc   512

查看Oracle数据库sga和memory max
 

SQL> show parameter sga

NAME                                 TYPE        VALUE
------------------------------------ ----------- -------lock_sga                             boolean     FALSE
pre_page_sga                         boolean     FALSE
sga_max_size                         big integer 1584M
sga_target                           big integer 0

 

 

SQL>  show parameter memory

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
hi_shared_memory_address             integer     0
memory_max_target                    big integer 1584M
memory_target                        big integer 1584M
shared_memory_address                integer     0

1584M远超过了操作系统共享内存大小512M

 

解决这个问题可以从两个层面（数据库和操作系统）:
1.数据库层面：修改初始化参数，使得初始化参数中sga或者memory的设置小于/dev/shm的大小
 

alter system set  memory_max_target=480M

使得数据库共享内存小于操作系统共享内存大小

2.操作系统层面：调整/dev/shm的大小
 

vim /etc/sysctl.conf
# Controls the maximum shared segment size, in bytes
kernel.shmmax = 68719476736

 ①修改shammax值，增大系统上的共享内存大小
 

sysctl -p

内核参数立即生效

或者②修改/dev/shm的大小可以通过修改/etc/fstab来实现：

 

 查看/dev/shm的空间大小

#df -h /dev/shm/
Filesystem            Size  Used Avail Use% Mounted on
tmpfs                 2.0G  1.3G  696M  65% /dev/shm

 

 

# vim /etc/fstab
tmpfs /dev/shm tmpfs defaults 0 0
tmpfs /dev/shm tmpfs defaults,size=10240M 0 0

 

 

 

重新挂载/dev/shm，再次查看/dev/shm的空间大小

#mount  -o remount /dev/shm
#df -h /dev/shm/
Filesystem            Size  Used Avail Use% Mounted on
tmpfs                  10G  1.3G  8.8G  13% /dev/shm

再次启动数据库问题解决！