Environment:
DB version: 12.1.0.2 (I think the behaviour is same for 11.2 as well)
Platform : Oracle Linux 6.6
Using Automatic Shared Memory Management (ie. we are not using MEMORY_TARGET )
We created a stand-alone Non-ASM, non-Container DB with 8GB SGA_TARGET . We forgot to configure Huge pages.
# grep -i HugePages_Total /proc/meminfo
HugePages_Total: 0
/dev/shm doesn't seem to be used because the Used column is showing 0 in the below output
$ df -PTh /dev/shm
Filesystem Type Size Used Avail Use% Mounted on
tmpfs tmpfs 7.9G 0 7.9G 0% /dev/shm
So, now , the server will be using the standard pagesize of 4KB. ie. To hold 8GB worth of SGA segments , you need 2097152 pages !
8388608/4 = 2097152
Hope my above calculation is correct . (8388608 KB = 8GB BTW)
Since using 4KB pagesize can be detrimental to performance and we don't want to use Huge pages, We are thinking of increasing /dev/shm to 9GB so that it could accomodate 8GB of SGA .
But does ASMM (Manually specfiying SGA_TARGET and PGA_AGGREGATE_TARGET) use /dev/shm ?