Hello ,
in addition to Fidel Vales comments , i can add one point.
Even if you do not use Automatic Memory management in Oracle 11 ,
there is still new feature works = "Automatic Shared Pool Extensions" , this means
if system detects that shared_pool is not bigenough , and you are about to have ORA-04031 error ,
it will automatically extend this pool , without any SGA_TARGET or MEMORY_TARGET configuration. I have seen this many times in our systems , this works more predictable and more
in accurate way (at least we didn't have problem with this).
You can disable this feature as well --> MEMORY_IMM_MODE_WITHOUT_AUTOSGA = FALSE
(but again if it works well , do not disable it).
P.S. why you need PGA=5GB in such memory-limited system , especially you have ECC as mentioned ?
Regards , Sergo.