在看 mysql5.7 的手册,看到 Optimization 章节时,发现这一段
• Otherwise, any index on col_name is nonunique and the optimizer can estimate the row count for each
range using dives into the index or index statistics.
With index dives, the optimizer makes a dive at each end of a range and uses the number of rows in the
range as the estimate. For example, the expression col_name IN (10, 20, 30) has three equality
ranges and the optimizer makes two dives per range to generate a row estimate. Each pair of dives yields
an estimate of the number of rows that have the given value.
Index dives provide accurate row estimates, but as the number of comparison values in the expression
increases, the optimizer takes longer to generate a row estimate. Use of index statistics is less accurate
than index dives but permits faster row estimation for large value lists.
查了一下有道词典,dive 翻译为潜水,俯冲,知乎上有个 DBA 翻译了这个章节,也翻译成潜水,总感觉不对.
请教各位,这里面的 dive 和 dive into 该如何理解?