mongodb - MongoDB _id (ObjectId) 是升序生成的吗？

Question

我知道当文档被插入到集合中时 _id 列如何包含时间戳的表示。这是一个在线实用程序，可将其转换为时间戳:http://steveridout.github.io/mongo-object-time/

我想知道的是对象id字符串本身是否保证保持升序？即这种比较是否总是返回真？

“最新对象 id”>“第二个最新对象 id”

Answer 1

不，没有任何保证。来自 official documentation (at the time of the original answer) :

The relationship between the order of ObjectId values and generation time is not strict within a single second. If multiple systems, or multiple processes or threads on a single system generate values, within a single second; ObjectId values do not represent a strict insertion order. Clock skew between clients can also result in non-strict ordering even for values, because client drivers generate ObjectId values, not the mongod process.

从latest docs

While ObjectId values should increase over time, they are not necessarily monotonic. This is because they:

Only contain one second of temporal resolution, so ObjectId values created within the same second do not have a guaranteed ordering, and Are generated by clients, which may have differing system clocks.