问题在于统计数据并不是对现实的客观衡量；它们只是一个最佳估测值。

The problem is that the statistics aren't an objective measure of reality; they are simply a best approximation.

youdao

这个值包含调整内存堆大小花费的时间和收集调优决策所需的统计数据花费的时间。

This value includes the time spent resizing the memory heaps and the time spent collecting statistics to make the tuning decision.

youdao

如果查询谓词中引用的列存在显著的数据值倾斜，那么要确保DB 2了解这一情况，最好是使用RUNSTATS生成列值柱状图统计数据。

If a significant data value skew exists for a column referenced in a query predicate, make sure that DB2 knows this, preferably by generating column-value histogram statistics using RUNSTATS.

youdao