DB terms ABC - ACID, BASE and CAP

 

ACID is an acronym which is commonly used to define the properties of a relational database system, it stand for following terms 

  • Atomicity - This property guarantees that if one part of the transaction fails, the entire transaction will fail, and the database state will be left unchanged. 

  • Consistency - This property ensures that any transaction will bring the database from one valid state to another. 

  • Isolation - This property ensures that the concurrent execution of transactions results in a system state that would be obtained if transactions were executed serially. 

  • Durable - means that once a transaction has been committed, it will remain so, even in the event of power loss. 



BASE properties are the common properties of recently evolved NOSQL databases. According to CAP theorem, a BASE system does not guarantee consistency. This is a contrived acronym that is mapped to following property of a system in terms of the CAP theorem 

  • Basically available indicates that the system is guaranteed to be available 

  • Soft state indicates that the state of the system may change over time, even without input. This is mainly due to the eventually consistent model. 

  • Eventual consistency indicates that the system will become consistent over time, given that the system doesn't receive input during that time

  •  


CAP theorem for distributed computing was published by Eric Brewer, This states that it is not possible for a distributed computer system to simultaneously provide all three of the following guarantees: 

  1. Consistency (all nodes see the same data even at the same time with concurrent updates ) 

  1. Availability (a guarantee that every request receives a response about whether it was successful or failed) 

  1. Partition tolerance (the system continues to operate despite arbitrary message loss or failure of part of the system) 

 
The CAP acronym corresponds to these 3 guarantees. This theorem has created the base for modern distributed computing approaches. World's most high volume traffic companies (e.g. Amazon, Google, Facebook) use this as basis for deciding their application architecture. It's important to understand that only two of these three conditions can be guaranteed to be met by a system.  


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