Consistency model
本章讨论consistency model。
含义
"consistency"的含义是"一致"。
multiple的各个entity之间保持consistency，在computer science中，主要是data 保持consistency。
下面是一些例子:
Memory and database
在drdobbs Generic: Change the Way You Write Exception-Safe Code — Forever 中描述了这样的情况:
void User::AddFriend(User& newFriend)
{
// Add the new friend to the vector of friends
// If this throws, the friend is not added to
// the vector, nor the database
friends_.push_back(&newFriend);
// Add the new friend to the database
pDB_->AddFriend(GetName(), newFriend.GetName());
}
This definitely causes consistency in the case of vector::push_back failing. Unfortunately, as you consult UserDatabase::AddFriend's documentation, you discover with annoyance that it can throw an exception, too! Now you might end up with the friend in the vector, but not in the database!
什么时候需要考虑consistency？
HA的一种方式是replication，这就同时存在着多个entity，如果是data system的话，就涉及如何保证这些entity之间的data的consistency。
TODO
csdn Zookeeper专题——3、分布式一致性，几种实现的优缺点
jianshu 取代 ZooKeeper！高并发下的分布式一致性开源组件 StateSynchronizer
mwhittaker Replicated Data Consistency Explained Through Baseball