Question

ORA-00845: MEMORY_TARGET not supported on this system

linux系统，执行数据库实例重启的时候报该错误。有哪位专家能提供解决的办法吗？不知道这个参数如何设置，现在有几个实例都启动不了，之前是正常的，也不知道其他的人是否对这个参数进行过别的设置

Answer 1

解决Linux上11g的ORA-00845错误
下午想把一个11.2.0.2实例的memory_target AMM内存初始化参数修改到2000M，改好后重启发现实例起不来了，出现了ORA-00845错误:
[oracle@rh2 ~]$
[oracle@rh2 ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.2.0 Production on Tue May 3 19:43:50 2011

Copyright (c) 1982, 2010, Oracle. All rights reserved.

Connected to an idle instance.

SQL> startup nomount;
ORA-00845: MEMORY_TARGET not supported on this system

======================= ALERT.LOG======================

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 2097152000 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 1871466496 and used is 200790016 bytes.
Ensure that the mount point is /dev/shm for this directory.
memory_target needs larger /dev/shm

看起来是因为采用了Automatic Memory Management的特性，所以Oracle采用了一种基于POSIX的共享内存使用风格，在AMM中Oracle不像之前版本那样利用”一整块”内存作为SGA，而是使用一块块小的”chunk”，以满足SGA与PGA之前交换内存的目的，具体可以参考下图:

针对上述ORA-00845错误，我们需要修改映射内存文件夹/dev/shm的装载参数，针对正在运行的Linux操作系统，可以remount这个tmpfs装载点，如:

http://www.askmaclean.com/archives/%E8%A7%A3%E5%86%B3linux%E4%B8%8A11g%E7%9A%84ora-00845%E9%94%99%E8%AF%AF.html