Oracle 11g的数据库，打算将SGA设大一点，知道 11g 中有一个新特新 MEMORY_TARGET，于是尝一下鲜，谁知报了个 ORA-00845，报错比较容易迷惑人，不借助Google真得想半天：

SQL> alter system set memory_max_target=3G scope=spfile ;

System altered.

SQL> alter system set memory_target=2G scope=spfile ;

System altered.

SQL>

SQL> shutdown immediate

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL> startup ;

ORA-00845: MEMORY_TARGET not supported on this system

      来自Oracle的官方解析是：

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 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.

      简单来说就是 MEMORY_MAX_TARGET 的设置不能超过 /dev/shm 的大小：

1 2	[oracle@FWDB FWDB]$ df -h | grep shm tmpfs                 2.0G     0  2.0G   0% /dev/shm

      还真是撞到这个枪口上了：

      马上把它加大：

[root@MHD-DB-SERVER oradata]# df -h | grep shm

tmpfs 15G 4.8G 11G 32% /dev/shm

[root@MHD-DB-SERVER oradata]# vi /etc/fstab

#

# /etc/fstab

# Created by anaconda on Fri Dec 30 10:53:45 2011

#

# Accessible filesystems, by reference, are maintained under '/dev/disk'

# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info

#

UUID=fbab7ba9-ed56-4174-b3f1-b90c218fa9f2 / ext4 defaults 1

1

UUID=562a97c7-d64a-4d1b-bc7f-fddc202b80db /boot ext4 defaults 1

2

UUID=90980dc0-af52-40f1-8641-6f0b36e858c5 /data ext4 defaults 1

2

UUID=d240a53e-7f8d-4b7a-9a75-28a422529c51 /tmp ext4 defaults 1

2

UUID=072c9d69-7cc1-4b17-88b6-ddc0a691bad8 /usr ext4 defaults 1

2

UUID=1c956757-a2bd-48c7-8786-f13d50db4616 /var ext4 defaults 1

2

UUID=a3d5231b-6e82-4899-afcf-20ac6979aa56 swap swap defaults 0

0

#tmpfs /dev/shm tmpfs defaults 0 0

tmpfs /dev/shm tmpfs defaults,size=20G 0 0

devpts /dev/pts devpts gid=5,mode=620 0 0

sysfs /sys sysfs defaults 0 0

proc /proc proc defaults 0 0

~

"/etc/fstab" 20L, 1261C written

[root@MHD-DB-SERVER oradata]# mount -o remount /dev/shm

[root@MHD-DB-SERVER oradata]# df -h /dev/shm

文件系统 容量 已用 可用 已用%% 挂载点

tmpfs    25G 12G 14G  48% /dev/shm

[root@MHD-DB-SERVER oradata]#

 

      再次启动数据库，没有报错了。