memory target

Hi,

On 11.2.0.4

what is the difference for performance between:

NAME                 TYPE    VALUE

------------------------------------ ----------- ------------------------------

memory_max_target          big integer 0

memory_target            big integer 0

And :

NAME                 TYPE    VALUE

------------------------------------ ----------- ------------------------------

memory_max_target          big integer 6G

memory_target            big integer 6G

Which one is better for performance?

Thanks.