"从人们开始对地表的特殊岩层进行编目和分类时起，大家就开始期望能够以某种方式利用这些岩层来计算地质年代。
Ever since people had begun to catalog the strata in particular outcrops, there had been the hope that these could somehow be used to calculate geological time.
由于对节省空间的计算只基于系统编目中的统计信息，所以这种计算速度很快。
As the calculation of the savings is based just on statistics information in the system catalog, the calculation is fast.
然后，优化器可以将输入变量的值与编目统计进行比较，并为谓词计算出一个更好的选择估计。
The optimizer can then compare the input variable values to catalog statistics and compute a better selectivity estimate for predicates.
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