验证OWI计数差异
select a.value A , b.value B , c.value C , d.value D
from   (select sum(bbwait)as value
       from x$kcbwds) a,
       (select total_waits as value
       from v$system_event
       where event = 'buffer busy waits') b,
       (select sum(count) as value
       from v$waitstat ) c,
       (select sum(value) as value
       from v$segment_statistics
       where statistic_name = 'buffer busy waits') d;
      
        A          B          C          D
---------- ---------- ---------- ----------
        73          5         73          3
       
        原因是由于并非所有x$结构都受到锁存器保护。因此，在高度并发环境中，一定会出现此类计数差异。