mongodb - Mongodb 并发 findAndModify 与增量操作

Question

如果两个代理在 Mongo 集群上同时运行此更新查询，最后 updateVersion 的预期值是多少？

db.Task.findAndModify(
    {
        query:{"updateVersion":21},
        update:{$inc:{"updateVersion":1}}
    }
);

如果答案是“23”，有没有办法保证读/写同步操作？

Answer 1

MongoDB 有 FAQ section关于并发操作。

在你的例子中，write conflict可能会发生，但 MongoDB 仍会尝试执行这两个命令:

A situation in which two concurrent operations, at least one of which is a write, attempt to use a resource in a way that would violate constraints imposed by a storage engine using optimistic concurrency control. MongoDB will transparently abort and retry one of the conflicting operations.