CAP Theorem

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From CAP theorem - Wikipedia:

In database theory, the CAP theorem, also named Brewer’s Theorem after computer scientist Eric Brewer, states that any distributed data store can provide only two of the following three guarantees

• consistency
  • Every read receives the most recent write or an error.
• Availability
  • Every request received by a non-failing node in the system must result in a response. This is the definition of availability in CAP theorem as defined by Gilbert and Lynch.[1] Note that availability as defined in CAP theorem is different from high availability in software architecture.
• Partition tolerance
  • The system continues to operate despite an arbitrary number of messages being dropped (or delayed) by the network between nodes.

When a network partition failure happens, it must be decided whether to do one of the following:

• cancel the operation and thus decrease the availability but ensure consistency
• proceed with the operation and thus provide availability but risk inconsistency. Note this doesn’t necessarily mean that system is highly available to its users

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