Cap theory and base theory

1. cap Theory and base theory
   1. CAP theory
   2. BASE theory
   3. Distributed transactions
   4. summary

cap Theory and base theory

CAP theory

cap Theory is an important concept in distributed systems ,c For consistency ,consistency, It is used to indicate that the data under the distributed system is consistent

a Indicates availability ,availability, Indicates that the service provided externally is always available

p It's partition fault tolerance ,partition tolerance, In other words, the problem of network partition in the distributed system can also ensure the availability of external services , The so-called network partition is that the distributed system is divided into different independent areas due to network failure . The fault tolerance of network partition must be guaranteed , Otherwise, it is not called distributed system if it is divided into different independent fields , It's a single system .

Then the service support can be provided after the data synchronization in the distributed system , This is it. CP, Guarantee consistency

The data of distributed system does not require strong consistency , First, ensure that the services are available , This is it. AP, Guaranteed availability

BASE theory

CAP In theory CP or AP,BASE The theory is to keep the service available for a period of time , Data inconsistency ,BASE Theory has three characteristics ：Basically Available, Basically available , The second characteristic is Soft State, Indicates a soft state , That is to say, the system has an intermediate state , At this time, the system can have inconsistent data, but the system as a whole is available , The third characteristic is Eventually consistent , That's final consistency , Ensure the final consistency of distributed project implementation data , For example, when calling wechat or Alipay, you don't need to wait for payment , But there is an inconsistent state at this time of operation , The consistency will be guaranteed after the payment is successfully callback

Distributed transactions

The ideas involved in distributed transactions include two-phase commit and three-phase commit , Two stage submission is divided into preparation stage and submission stage , In the preparation phase, the coordinator first asks all services involved in the transaction whether they can submit , All services participating in the transaction execute the transaction first and send it to the coordinator. Is it successful or aborted , The submission phase is when the coordinator receives a message from the participants, one of which is an abort message, and all participants will be rolled back , Otherwise, submit

summary

This article talks about the related content of distributed transactions , Include CAP theory 、BASE theory , Finally, the concept of distributed transaction is introduced , These theories are to better understand distributed transactions , Including his evolution .