参考：http://www.eygle.com/archives/2011/02/dba_event_10046_10053.html
上文中的例子，过程概述：
1）查看执行计划显示的“疑问表”的行数rows_A；
2）查看10053 event trace中显示的“疑问表”的行数rows_B；
rows_A是统计信息中的值，rows_B是实际计算的值。
文章示例是在9i下的，以下是11g的示例，与9i略有不同。
点击(此处)折叠或打开
-
-----------------------------
-
SYSTEM STATISTICS INFORMATION
-
-----------------------------
-
Using NOWORKLOAD Stats
-
CPUSPEEDNW: 3074 millions instructions/sec (default is 100)
-
IOTFRSPEED: 4096 bytes per millisecond (default is 4096)
-
IOSEEKTIM: 10 milliseconds (default is 10)
-
MBRC: NO VALUE blocks (default is 8)
-
-
***************************************
-
BASE STATISTICAL INFORMATION
-
***********************
-
Table Stats::
-
Table: SUM$ Alias: S
-
#Rows: 1 #Blks: 1 AvgRowLen: 129.00 ChainCnt: 0.00
-
Index Stats::
-
Index: SYS_IL0000001030C00030$$ Col#: (NOT ANALYZED)
-
LVLS: 1 #LB: 25 #DK: 100 LB/K: 1.00 DB/K: 1.00 CLUF: 800.00
-
Index: SYS_IL0000001030C00031$$ Col#: (NOT ANALYZED)
-
LVLS: 1 #LB: 25 #DK: 100 LB/K: 1.00 DB/K: 1.00 CLUF: 800.00
-
Index: I_SUM$_1 Col#: 1
-
LVLS: 0 #LB: 1 #DK: 1 LB/K: 1.00 DB/K: 1.00 CLUF: 1.00
-
***************************************
-
1-ROW TABLES: SUM$[S]#0
-
Access path analysis for SUM$
-
***************************************
-
SINGLE TABLE ACCESS PATH
-
Single Table Cardinality Estimation for SUM$[S]
-
Column (#1): OBJ#(
-
AvgLen: 5 NDV: 1 Nulls: 0 Density: 1.000000 Min: 81279 Max: 81279
-
Column (#11): XPFLAGS(
-
AvgLen: 6 NDV: 1 Nulls: 0 Density: 1.000000 Min: 67108864 Max: 67108864
-
Table: SUM$ Alias: S
-
Card: Original: 1.000000 Rounded: 1 Computed: 0.01 Non Adjusted: 0.01
-
Access Path: TableScan
- Cost: 2.00 Resp: 2.00 Degree: 0