ORA-845: MEMORY_TARGET not supported on this system

ORA-845: MEMORY_TARGET not supported on this system
===================================================

For:-

Oracle Server Version: 11.1.0.6 to 11.2.0.2.0 - Release: 11.1 to 11.2
Linux x86-64

Problem :-
=========

On a Linux system, trying to start up an 11g instance could fail with the following error:

ORA-845: MEMORY_TARGET not supported on this system

In the alert log, you could or could not see the below messages:

ORA-04031 errors

OR

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 bytes.The /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 and used is bytes.memory_target needs larger /dev/shm

If ORA-04031 is seen in the alert log, sometimes you can not establish new connections due to this problem.


======================
Cause of error
======================

AMM (Automatic Memory Management) is a new feature in 11 which manages both SGA and PGA.

MEMORY_TARGET is used instead of SGA_TARGET and MEMORY_MAX_TARGET is used instead of SGA_MAX_SIZE (defaults to MEMORY_TARGET ).

It uses /dev/shm on Linux. If max_target set over /dev/shm size, you get the error messages.



====================
Solution
====================

1. If you are installing Oracle 11g on a Linux system, note that Memory Size (SGA and PGA), which sets
the initialization parameter MEMORY_TARGET or MEMORY_MAX_TARGET, cannot be greater than the shared memory filesystem (/dev/shm) on your operating system. To resolve the current error, increase the /dev/shm file size. For example:

# mount -t tmpfs shmfs -o size=7g /dev/shm

Also, to make this change persistent across system restarts, add an entry in /etc/fstab similar to the following:

shmfs /dev/shm tmpfs size=7g 0

2. This error may also occur if /dev/shm is not properly mounted. Make sure your df output is similar to the following:

$ df -k
Filesystem 1K-blocks Used Available Use% Mounted on
...
shmfs 6291456 832356 5459100 14% /dev/shm

3. If configuring AMM is not possible due to lack of space on /dev/shm mount point, you can configure ASMM instead of AMM, i.e. set SGA_TARGET, SGA_MAX_SIZE and PGA_AGGREGATE_TARGET instead of MEMORY_TARGET.