好吧，ora-01555

演示：

--session# 1
drop table test;
create table test(id int,name varchar2(10));
insert into test values (1,'a');
insert into test values (2,'b');
commit;

variable i refcursor;
exec open :i for select *from test;
print i;

--session# 2
declare
  i number:= 1;
begin
  loop
  update test set id = i where name = 'a';
    i:= i + 1;
    if mod(i, 100) = 0 then
    commit;
end
if;
 end loop;
end;
/

-- 等待 10秒

--session# 1
print i;

会收到提示：
ERROR:
ORA-01555: snapshot too old: rollback segment number 15 with name "_SYSSMU15_1396376464$" too small
Ctrl +C 中断session# 2