Distributed base theory

What is? BASE

eBay Architect Dan Pritchett From the practice summary of large-scale distributed system , stay ACM Put forward in an article published on BASE theory ,BASE The theory is right CAP The extension of theory , The core idea is that even if strong consistency cannot be achieved （Strong Consistency,CAP Consistency is strong consistency ）, But the application can achieve final consistency in a suitable way （Eventual Consitency）.

1. Basically Available（ Basic available ） In case of unpredictable failure of distributed system , Partial loss of availability is allowed
2. Soft state（ Soft state ） Soft state is also called weak state , As opposed to the hard state , It means that the data in the system is allowed to exist in an intermediate state , The existence of the intermediate state will not affect the overall availability of the system , That is to say, there is a delay in the process of data synchronization between data copies of different nodes .
3. Eventually consistent（ Final consistency ） Finally, consistency emphasizes all copies of data in the system , After a period of synchronization , Eventually a consistent state can be reached . therefore , The essence of final consistency is to ensure that the final data can be consistent , It does not need to guarantee the strong consistency of system data in real time

CAP And BASE Relationship

BASE It's right CAP The result of the trade-off between consistency and availability , It comes from the conclusion of distributed practice of large-scale Internet system , Is based on CAP The theorem evolved gradually , The core idea is that even if strong consistency cannot be achieved （Strong consistency）, More specifically , It's right CAP in AP A supplement to the plan . The basic idea is ： Through business , Gain usability at the expense of strong consistency , And allow data to be inconsistent over time , But it finally reached a consistent state .

CAP And ACID Relationship

ACID It is a common design concept of traditional database , The pursuit of a strong consistency model .BASE It supports large distributed systems , High availability is achieved by sacrificing strong consistency .

ACID and BASE Represents two completely opposite design philosophy , In the scenario of distributed system design , System components have different requirements for consistency , therefore ACID and BASE It will be used in combination with .

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