Guenadi N Jilevski's Oracle BLOG

MEMORY_TARGET not supported on this system ORA-00845

 MEMORY_TARGET not supported on this system – ORA-00845

Starting from Oracle 11g the automatic memory management feature is  defined with MEMORY_TARGET and MEMORY_MAX_TARGET parameters . The Automatic Memory Management (AMM) manages both SGA and PGA. The user specifies a value for MEMORY_TARGET and the max value that the parameter can grow is limited by MEMORY_MAX_TARGET. Once the MEMORY_TARGET is set Oracle determines the values for SGA_TARGET and PGA_AGGREGATE_TARGET. User does not need to set the above parameter values, instead can rely on Oracle to control those parameters value. Prior to Oracle 11g the user was responsible to set the SGA_TARGET and PGA_AGGRAGATE_TARGET. On Linux based systems the shared memory file system has to be mounted on /dev/shm. The MEMORY_MAX_TARGET need to be less than the shared memory mounted on /dev/shm. Make sure the shared memory filesystem is big enough for Automatic Memory Manager to work.

How to mount shared memory file system ? Execute as root.

# umount tmpfs
# mount -t tmpfs shmfs -o size=4500m /dev/shm

How to make the shared memory file system persistent across reboots?  Add an entry in /etc/fstab.

shmfs /dev/shm tmpfs size=4500m 0 

The ORA-00845 error usually appears if MEMORY_MAX_TARGET is set to a value greater or equal to the amount of memory allocated for /dev/shm.

Make sure that /dev/shm is mounted and there is sufficient memory for the shared memory file system to support AMM in Oracle.

Make sure that Oracle parameters MEMORY_MAX_TARGET, MEMORY_TARGET are less that the memory allocated to the shared memory file system in /dev/shm.

August 12, 2010 - Posted by gjilevski | oracle