mongodb在CAP定理中站在哪里？ [英] Where does mongodb stand in the CAP theorem?

问题描述

到处都是，我看到MongoDB是CP。
但是当我挖入我看到它是最终一致。
当您使用safe = true时是否为CP？如果是这样，那是否意味着当我使用safe = true写时，所有副本都会在获得结果之前更新。

Everywhere I look, I see that MongoDB is CP. But when I dig in I see it is eventually consistent. Is it CP when you use safe=true? If so, does that mean that when I write with safe=true, all replicas will be updated before getting the result?

推荐答案

默认情况下，MongoDB是强一致的 - 如果你做一个写，然后做一个读，假设写成功，你将永远能够读取你刚刚读的结果。这是因为MongoDB是单主机系统，并且所有读取在默认情况下转到主服务器。如果您可以选择启用从次要的读取，那么MongoDB最终会一致，从而可能读取过时的结果。

MongoDB is strongly consistent by default - if you do a write and then do a read, assuming the write was successful you will always be able to read the result of the write you just read. This is because MongoDB is a single-master system and all reads go to the primary by default. If you optionally enable reading from the secondaries then MongoDB becomes eventually consistent where it's possible to read out-of-date results.

MongoDB也通过自动故障切换获得高可用性副本集： http://www.mongodb.org/display/DOCS/Replica+Sets

MongoDB also gets high-availability through automatic failover in replica sets: http://www.mongodb.org/display/DOCS/Replica+Sets

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