1 活动会话历史趋向
select to_char(sample_time,'yyyy-mm-dd hh24:mi:ss'),count(1)
from dba_hist_active_sess_history
where sample_time>sysdate-2/24
and sample_time<sysdate-1/24
group by to_char(sample_time,'yyyy-mm-dd hh24:mi:ss')
如果数据库存在异常，或者突然增加幅度较大，则此时用户请求以及
via receive message bytes from client，user calls parse count，transaction个数