create table trans_check as select * from dual
/

create package trans_level as
function is_readonly return boolean;
function is_serialize return boolean;
function level_name return varchar2;
end;
/

create package body trans_level as

DB_readonly exception;
cant_serialize exception;
pragma exception_init(DB_readonly, -1456);
pragma exception_init(cant_serialize, -8177);

function is_readonly return boolean is
begin
	savepoint a;
	update trans_check set dummy=dummy;
	rollback to a;
	return false;
exception
	when DB_readonly then
		return true;
end;

function is_serialize return boolean is
	val trans_check.dummy%type;

	procedure try_upd is
		pragma autonomous_transaction;
	begin
		update trans_check set dummy=dummy;
		commit;
	end;
begin
	savepoint a;
	select dummy into val from trans_check;
	try_upd;
	update trans_check set dummy=dummy;
	rollback to a;
	return false;
exception
	when cant_serialize then
		return true;
	when DB_readonly then
		return false;
end;

function level_name return varchar2 is
begin
	return case when is_readonly then 'READ ONLY'
		    when is_serialize then 'SERIALIZABLE'
		    else 'READ COMMITED'
		end;
end;

end;
/