TIP 96#: Good to know/be reminded of (2)

In my effort to share some basics which are forgotten/missed,for today, I have the following two items

Index for FK columns

Do I need FK index for every single FK columns, I would say yes, unless the following conditions are met

1. The primary key in parent table is not updated.
2. The record in the parent table is not deleted. (Either with delete cascade or without)
3. The primary and child table are not accessed together in a join condition.

The benefit that you gain from indexed FK in one of this condition at least is not met is much higher than being without index

Out of memory as instance startup

DB box has enough physical memory but when you startup instance with SGA much lower than free physical memory, you get out of memory.
This is most likely due to shmall and shmmax, shmall is total shared memory which can be used in the system and shmmax is the max bite(chunk) which can be allocated.
If shmall is lower than SGA, you will see the issue

getconf PAGESIZE
cat /proc/sys/kernel/shmall

max shared size = 4194304x4096 Bytes= 16G
SGA can not be set to higher than 16GB although
box has 32 or 64GB or much higher.