最近遇到两次在sp报告中，显示逻辑读为负数。进行分析情况如下：
一台是运营商的crm库（aix 5.3+9.2.0.8+rac）

--系统版本
[zwq_crm2:/home/crm_oraeye]oslevel -s
5300-08-07-0920
--数据库版本
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle9i Enterprise Edition Release 9.2.0.8.0 - 64bit Production
PL/SQL Release 9.2.0.8.0 - Production
CORE    9.2.0.8.0       Production
TNS for IBM/AIX RISC System/6000: Version 9.2.0.8.0 - Production
NLSRTL Version 9.2.0.8.0 - Production
--数据库启动时间
SQL> SELECT A.INST_ID, TO_CHAR (startup_time, 'yyyy-mm-dd hh24:mi:ss')
  2   FROM gv$instance a;
   INST_ID TO_CHAR(STARTUP_TIM
---------- -------------------
         2 2011-02-19 03:33:49
         1 2011-02-19 03:56:17
--异常的逻辑读统计数据
SQL>   SELECT b.snap_id,
  2           TO_CHAR (B.SNAP_TIME, 'yyyy-mm-dd hh24:mi:ss'),
  3           TO_CHAR (A.VALUE, '999,999,999,999,999')
  4      FROM stats$sysstat a, stats$snapshot b
  5     WHERE     a.NAME = 'session logical reads'
  6           AND a.instance_number = 2
  7           AND a.snap_id = b.snap_id
  8           AND A.SNAP_ID >=47913
  9           AND A.SNAP_ID <=47920
 10  ORDER BY a.snap_id;
   SNAP_ID TO_CHAR(B.SNAP_TIME TO_CHAR(A.VALUE,'999
---------- ------------------- --------------------
   47913	2012-02-10 20:00	4,764,705,272,783
   47914	2012-02-10 21:00	4,761,539,910,574
   47915	2012-02-10 22:00	4,749,529,436,021
   47916	2012-02-10 23:00	4,745,952,040,146
   47917	2012-02-11 00:00	4,738,052,256,634
   47918	2012-02-11 01:00	4,738,894,245,521
   47919	2012-02-11 02:00	4,739,587,095,184
   47920	2012-02-11 03:00	4,740,409,262,259

另一台是运营商的开停机库（aix 5.3+9.2.0.8+rac）

--系统版本
[zwq_offon2:/home/oraeye]oslevel -s
5300-08-07-0920
--数据库版本
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle9i Enterprise Edition Release 9.2.0.8.0 - 64bit Production
PL/SQL Release 9.2.0.8.0 - Production
CORE    9.2.0.8.0       Production
TNS for IBM/AIX RISC System/6000: Version 9.2.0.8.0 - Production
NLSRTL Version 9.2.0.8.0 - Production
--数据库启动时间
SQL> SELECT A.INST_ID, TO_CHAR (startup_time, 'yyyy-mm-dd hh24:mi:ss')
  2    FROM gv$instance a;
   INST_ID TO_CHAR(STARTUP_TIM
---------- -------------------
         2 2010-01-23 19:16:46
         1 2010-01-23 19:15:09
--异常的逻辑读统计数据
SQL>   SELECT b.snap_id,
  2           TO_CHAR (B.SNAP_TIME, 'yyyy-mm-dd hh24:mi:ss'),
  3           TO_CHAR (A.VALUE, '999,999,999,999,999')
  4      FROM stats$sysstat a, stats$snapshot b
  5     WHERE     a.NAME = 'session logical reads'
  6           AND a.instance_number = 2
  7           AND a.snap_id = b.snap_id
  8           AND A.SNAP_ID IN ('38271', '38272', '38339', '38340')
  9  ORDER BY a.snap_id;
   SNAP_ID TO_CHAR(B.SNAP_TIME TO_CHAR(A.VALUE,'999
---------- ------------------- --------------------
     38271 2012-01-31 19:00:05    4,269,858,122,434
     38272 2012-01-31 20:00:02    4,266,001,522,867
     38339 2012-02-02 09:00:02    4,275,651,080,526
     38340 2012-02-02 10:00:02    4,250,263,107,466

这两个数据库中都出现了在数据库没有重启的情况下stats$sysstat.value的值出现波动情况，而且都是在40万亿以上的时候。不知道是特点的版本巧合(特定的数据库版本，特定的操作系统版本)，还是Oracle未公布bug。出现这样的情况，目前只能通过重启实例来使得statspack捕获到的逻辑读值变小，从而避免这样的波动，从而解决sp中出现逻辑读为负数的情况。