如果您的存储支持每个键的线性化和比较和设置(对于MongoDB是这样的)，您可以在客户端实现原子多键更新(可序列化的事务)。这种方法在谷歌的Percolator和CockroachDB中使用，但没有什么可以阻止你在MongoDB中使用它。

我已经创建了这种交易的一步一步的可视化。我希望它能帮助你理解它们。

如果您不介意读提交隔离级别，那么有必要看看Peter Bailis的RAMP事务。它们也可以在客户端为MongoDB实现。

请阅读ACID属性以更好地理解。

此外，在MongoDB文档中，您可以找到一个问题和答案。

MongoDB不兼容ACID。阅读下面关于ACID的讨论 遵从性。

MongoDB is Atomic on document level only. It does not comply with the definition of atomic that we know from relational database systems, in particular the link above. In this sense MongoDB does not comply with the A from ACID. MongoDB is Consitent by default. However, you can read from secondary servers in a replica set. You can only have eventual consistency in this case. This is useful if you don't mind to read slightly outdated data. MongoDB does not guarantee Isolation (again according to above definition):

对于同时有多个读取器和写入器的系统，MongoDB可以 操作之前，允许客户端读取写入操作的结果 写操作返回。 如果mongod在日志提交之前终止，即使是写操作 返回成功，则查询可能已读取不存在的数据 mongod重启后。 但是，MongoDB会单独修改每个文档(用于插入和 更新);仅在文档级别上，而不在多文档事务上。

关于持久性——你可以用写关注选项来配置这种行为，但不确定。也许有人更清楚。

我相信一些正在进行的研究将NoSQL转向ACID约束或类似的约束。这是一个挑战，因为NoSQL数据库通常比较快，而ACID约束会显著降低性能。

“不能正确保存”可能意味着:

By default MongoDB does not save your changes to the drive immediately. So there is a possibility that you tell a user "update is successful", power outage happens and the update is lost. MongoDB provides options to control level of update "durability". It can wait for the other replica(s) to receive this update (in memory), wait for the write to happen to the local journal file, etc. There is no easy "atomic" updates to multiple collections and even multiple documents in the same collection. It's not a problem in most cases because it can be circumvented with Two Phase Commit, or restructuring your schema so updates are made to a single document. See this question: Document Databases: Redundant data, references, etc. (MongoDB specifically)

如果您的存储支持每个键的线性化和比较和设置(对于MongoDB是这样的)，您可以在客户端实现原子多键更新(可序列化的事务)。这种方法在谷歌的Percolator和CockroachDB中使用，但没有什么可以阻止你在MongoDB中使用它。

我已经创建了这种交易的一步一步的可视化。我希望它能帮助你理解它们。

如果您不介意读提交隔离级别，那么有必要看看Peter Bailis的RAMP事务。它们也可以在客户端为MongoDB实现。

从MongoDB v4.0开始，将支持多文档ACID事务。通过快照隔离，事务将提供全局一致的数据视图，并强制执行全有或全无的执行以维护数据完整性。

它们感觉像是来自关系世界的事务，例如:

with client.start_session() as s:
    s.start_transaction()
    try:
        collection.insert_one(doc1, session=s)
        collection.insert_one(doc2, session=s)
        s.commit_transaction()
    except Exception:
        s.abort_transaction()

参见https://www.mongodb.com/blog/post/multi-document-transactions-in-mongodb

“在MongoDB中，单个文档上的操作是原子的”——这是过去的事情

在MongoDB 4.0的新版本中，您可以:

However, for situations that require atomicity for updates to multiple documents or consistency between reads to multiple documents, MongoDB provides the ability to perform multi-document transactions against replica sets. Multi-document transactions can be used across multiple operations, collections, databases, and documents. Multi-document transactions provide an “all-or-nothing” proposition. When a transaction commits, all data changes made in the transaction are saved. If any operation in the transaction fails, the transaction aborts and all data changes made in the transaction are discarded without ever becoming visible. Until a transaction commits, no write operations in the transaction are visible outside the transaction.

尽管对于如何执行和执行什么操作有一些限制。

检查Mongo Doc。 https://docs.mongodb.com/master/core/transactions/