oracle 11g ORA-00845错误解决
oracle11g数据库，修改了内存参数memory_max_target=943718400,关闭数据库重新启动的时候报错
[oracle@instuctor shm]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.3.0 Production on Mon Nov 19 09:34:11 2012
Copyright (c) 1982, 2011, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup
ORA-00845: MEMORY_TARGET not supported on this system
SQL> exit
Disconnected
[oracle@instuctor shm]$ oerr ora 00845
00845, 00000, "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.
查看数据库的警告日志，同样看到了类似的报错信息
Mon Nov 19 09:34:14 2012
Starting ORACLE instance (normal)
WARNING: You are trying to use the MEMORY_TARGET feature. This feature requires the /dev/shm file system to be mounted for at least 943718400
bytes. /dev/shm is either not mounted or is mounted with available space less than this size. Please fix this so that MEMORY_TARGET can work
as expected. Current available is 845021184 and used is 208900096 bytes. Ensure that the mount point is /dev/shm for this directory.
memory_target needs larger /dev/shm
通过以上原因的分析，看来是/dev/shm剩余的空间太小了
[oracle@instuctor shm]$ df -H
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 17G 15G 1.2G 93% /
tmpfs 1.1G 209M 846M 20% /dev/shm
[oracle@instuctor shm]$
Oracle在metalink的文档：Doc ID:Note:460506.1中进行了说明。
解决这个问题只有两个方法，
1.修改初始化参数，使得初始化参数中SGA的设置小于/dev/shm的大小
2.调整/dev/shm的大小。
修改/dev/shm的大小可以通过修改/etc/fstab来实现：
[root@instuctor ~]# vi /etc/fstab
LABEL=/ / ext3 defaults 1 1
tmpfs /dev/shm tmpfs defaults,size=2G 0 0
devpts /dev/pts devpts gid=5,mode=620 0 0
sysfs /sys sysfs defaults 0 0
proc /proc proc defaults 0 0
LABEL=SWAP-sda2 swap swap defaults 0 0
~
~
[root@instuctor ~]# mount -o remount /dev/shm
[root@instuctor ~]# df -H
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 17G 15G 1.2G 93% /
tmpfs 2.2G 209M 2.0G 10% /dev/shm
扩大/dev/shm后，再次尝试启动数据库，没有问题。
[oracle@instuctor ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.3.0 Production on Mon Nov 19 10:02:33 2012
Copyright (c) 1982, 2011, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup
ORACLE instance started.
Total System Global Area 939495424 bytes
Fixed Size 2233960 bytes
Variable Size 616565144 bytes
Database Buffers 314572800 bytes
Redo Buffers 6123520 bytes
Database mounted.
Database opened.
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