Distributed Base theory

Just CAP theory ,C and A  Only one is guaranteed ：

CP, At the expense of functional integrity and availability

AP, At the expense of strong consistency

BASE(Basically Available, Soft State, Eventual Consistency  Basic available 、 Soft state 、 Final consistency ) Yes CAP AP The extension of theory . The core idea of theory is ： We can't achieve strong consistency , But each application can be based on its own business characteristics , Take appropriate measures to achieve the final consistency of the system .

Basic available ：

1. Lost response time >>> Add queue peak clipping operation

2. Loss of some functions >>>  Downgrade

Soft state ： The soft state is relatively atomic

• Atomicity （ Hard state ） >>>  The data copies of multiple nodes are required to be consistent , This is a kind of " Hard state "
• Soft state （ Weak state ） >>>  Allow data in the system to have intermediate states , It is considered that this state does not affect the overall availability of the system , That is, the system is allowed to have data delay in the data copies of multiple different nodes

Final consistency ：

The system can ensure that there is no other new update operation , The data will eventually reach a consistent state , Therefore, all client data access to the system can finally get the latest value .

Causal consistency （Causal consistency）

If node A After updating some data, the node is notified B, Then the node B The access modification operations of are all based on A Updated value , meanwhile , And nodes A There is no causal relationship C There are no such restrictions on data access

Read what you have written （Read your writes）

The specific form of causality , A node A You can always read your updated data

Conversation consistency （Session consistency）

Access the storage system with a valid session , The system shall ensure that the process reads what it has written

Monotonous reading consistency （Monotonic read consistency）

After a node reads a specific value from the system , Then the node will not read any previous value from the system

Monotonous writing consistency （Monotonic write consistency）

A system should be able to ensure that writes from the same node are executed in sequence （ Ensure that write operations are serialized ）