是否可以在 MongoDB 之上实现多版本并发控制 (MVCC)？
MongoDB 对我来说是一个很棒的数据库。然而，在某些情况下，我确实需要原子多文档事务。例如，在帐户之间转移事物（例如金钱或声誉），这需要完全成功或完全失败。
我想知道是否可以通过实现多版本并发控制模式的库与 MongoDB 进行交互。
表演会有多糟糕？ 使用混合方法是否可能且有利可图，仅在必要时使用“mongo-mvcc”库，而仅在处理单个文档时使用传统的数据库连接，或者这会破坏 mvcc 的东西吗？
MongoDB is to me a great database. However there are cases where I really need atomic multi-document transactions. For example to transfer things (like money or reputation) between accounts and this needs to either succeed completely or fail completely.
I wonder if it would be possible to interact with MongoDB through a library implementing the MultiVersion Concurrency Control pattern.
How bad would it be concerning performances?
Would it be possible and profitable to use a hybrid approach, using the 'mongo-mvcc' library only when necessary and the traditional db connection when working only on a single document or would this break the mvcc stuff ?
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最简单的方法是使用锁（两阶段提交），尽管这在某些情况下效率不是很高。对于更高的并发性，可以在 Mongo 之上实现某种 MVCC。本文提供了很好的描述：
http://highlyscalable.wordpress .com/2012/01/07/mvcc-transactions-key-value/
The simplest way is to use locks (two-phase commit), although this is not very efficient in some cases. For higher concurrency some kind of MVCC can be implemented on the top of Mongo. This article provides a good description:
http://highlyscalable.wordpress.com/2012/01/07/mvcc-transactions-key-value/
金钱交易可以通过两阶段提交来实现：http://www.mongodb。 org/display/DOCS/two-phase+commit
Money transaction can be implemented via two-phase commit : http://www.mongodb.org/display/DOCS/two-phase+commit
GitHub 上现在提供了 MongoDB 上的 MVCC 实现：
https://github.com/igd-geo/蒙戈姆VCC
There is an implementation of MVCC on MongoDB available now on GitHub:
https://github.com/igd-geo/mongomvcc
MongoDB 并不是真正为处理事务而设计的。关于如何实现这一点，有一个非常好的讨论：http://kylebanker.com/blog/2010/04/30/mongodb-and-ecommerce/
MongoDB isn't really designed to work with transactions. There is a really good discussion of how you might be able to implement this over at: http://kylebanker.com/blog/2010/04/30/mongodb-and-ecommerce/
您可以创建版本集合并拥有最后提交版本的文档。
使用读取时间戳 (rts) 以原子方式更新此文档，该时间戳不是基于时间的时间戳，而是当应用程序代码从集合中读取文档时单调递增的数字。
在更新集合之前，获取此版本集合文档并检查当前事务下方是否有读取时间戳，如果有，则中止读取或写入。
当您想要使用lastCommit“发布”记录的版本并使其可见时，请更新版本文档。
您应该只“查看”小于或等于最后提交的交易编号的交易数据。
我在此存储库中实现了 Java MVCC。
You could create a versions collection and have a document for the last committed version.
Atomically update this document with the Read Timestamp (rts) which is not a time based timestamp but a monotonically increasing number when your application code has read a document from a collection.
Before you update a collection, fetch this versions collection document and check if there is a read timestamp below your current transaction, if there is, abort the read or write.
Update the versions document when you want to "publish" with a lastCommit the version of a record and cause it to be visible.
You should only "see" transactions data that are less than or equal to the last committed transaction number.
I implemented MVCC in Java in this repository.
那么，当您需要真正的事务时，您可以使用 RDBMS，它们旨在支持它们:) NoSQL 速度更快且更具可扩展性，主要是因为它们不支持事务。
如果您两者都需要，那么使用事务层来支持事务并将 NoSQL 层用于其他目的也许是个好主意？在某些情况下，使用 MongoDB 和 PostgreSQL 创建混合系统应该不难
Well when you need real TRANSACTIONS you use RDBMS which are designed to support them :) NoSQLs are faster and more scalable mainly because they don't support transactions.
If you need both maybe it's a good idea to have transactional layer to support transactions and NoSQL layer for other purposes? In some cases it shouldn't be difficult to create a hybrid system using for example MongoDB and PostgreSQL