memory_target

MEMORY_TARGET，报了个 ORA-00845，：

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

1 [root@FWDB ~]# cat /etc/fstab | grep tmpfs
2 tmpfs                   /dev/shm                tmpfs   defaults,size=4G 0 0

      现在可以通过重启使这个配置生效，也可以通过重新挂载来修改其大小：

1 [root@FWDB ~]# mount -o remount,size=4G /dev/shm
2 [root@FWDB ~]# df -h | grep shm
3 tmpfs                 4.0G     0  4.0G   0% /dev/shm

      再次启动数据库，没有报错了。