Monday, January 22, 2018

ORA-00845: MEMORY_TARGET not supported on this system

If we face ORA-00845 during database startup, it would mean that /dev/shm file system is not configured with appropriate value required to start the database instance. We need to mount /dev/shm with a value that should be equal or more than the value of memory we want to allocate to all instances/SGAs (ASM as well as database instances) that would run on this host.
You may find following type of warning in alert log file.
WARNING: You are trying to use the MEMORY_TARGET feature. This feature requires the /dev/shm file system to be mounted for at least 914358272 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 911679488 and used is 667967488 bytes. Ensure that the mount point is /dev/shm for this directory.
Thu Mar 17 11:05:27 2016
memory_target needs larger /dev/shm

Above warning is because of low allocation to /dev/shm, as can be seen bellow.
[root@salman1 ~]# df -kh
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda3             116G   24G   86G  22% /
/dev/sda1            1008M   78M  880M   9% /boot
tmpfs                 1.5G     0  1.0G   66.6% /dev/shm

To fix this problem, we should add an entry similar to the following /etc/fstab file so that /dev/shm is set automatically after every server startup. I am setting /dev/shm to 8G for this example.
tmpfs                   /dev/shm                tmpfs   defaults,size=8G       0 0

Now shutdown all instances (ASM and/or database) currently running (if any), and unmounts /dev/shm.
[root@salman1 ~]# umount -l /dev/shm
[root@salman1 ~]# df -kh
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda3             116G   24G   86G  22% /
/dev/sda1            1008M   78M  880M   9% /boot

Issue following command to mount /dev/shm again based on the value set in /etc/fstab file, and check if this file system has been set to 8G.

[root@salman1 ~]# mount -a
[root@salman1 ~]# df -kh
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda3             116G   24G   86G  22% /
/dev/sda1            1008M   78M  880M   9% /boot
tmpfs                 8.0G     0  8.0G   0% /dev/shm

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