Automatic Memory Management in 11g
Posted by Pavan DBA on July 21, 2010
All of us by this time would have known about 11g new feature AMM. This allows to manage both SGA and PGA automatically by setting MEMORY_TARGET and MEMORY_MAX_TARGET parameters.
Now i got a doubt on how oracle will do this? i.e releasing shared memory and allocating it to private memory…
After so many searches in google, finally i found following
1. Oracle in 11g is using /dev/shm mount point for shared memory implementation
2. this is called Linux POSIX oriented SHM implementaion
So now all memory segments are treated as files on that mount point. If any one requires extra segment, Oracle will simply allocate the file which is free.
If you don’t have /dev/shm mounted (default it will be mounted), then you cannot use MEMORY_TARGET parameter and this will also happen if you have less size for tmpfs in Linux.
Plz refer to below link where Tanel explained in wonderful way about this.