Wednesday, September 11, 2013

ORA-00845: MEMORY_TARGET not supported on this system using 11g on Linux

You are trying to use the Automatic Memory Management (AMM) has been implemented by setting parameters like MEMORY_TARGET and/or MEMORY_MAX_TARGET in a 11g database.

Starting with Oracle Database 11g, the Automatic Memory Management feature requires more shared memory (/dev/shm) and file descriptors. This feature requires the /dev/shm file system to be mounted with a size of bytes to accommodate the instance memory (SGA + PGA), meaning that it must be at least equal with the greater of the MEMORY_MAX_TARGET and MEMORY_TARGET.

The following example shows that if you try to start an instance with MEMORY_MAX_TARGET or MEMORY_TARGET with more than 4G the ORA-00845 error would be raised on startup

Filesystem            Size  Used Avail Use% Mounted on
tmpfs                  12G  8.3G  3.8G  69% /dev/shm

So do the following :

As Oracle stop all the running instances on the machine

AS root : 

# mount -t tmpfs shmfs -o size=20g /dev/shm 
# vi /etc/fstab 
add or change the line for the /dev/shm filesystem to the following : 
shmfs /dev/shm tmpfs size=20g

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