db_keep_cache_size and db_cache_size parameters in 19c

If these parameters maintain default zero values, does 19c automatically increases the values on demand or these values need to be set with higher values?

SQL> show parameter db_keep_cache_size

NAME                 TYPE    VALUE

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

db_keep_cache_size          big integer 0

SQL> show parameter db_cache_size

NAME                 TYPE    VALUE

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

db_cache_size            big integer 0

SQL>