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）.

• Basically Available
  （ Basic available ） In case of unpredictable failure of distributed system , Partial loss of availability is allowed

• 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 .

• 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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