Cap Theorm or Brewer’s Theorm and OpenStack Swift

Posted: December 21, 2012 in Uncategorized

In theoretical computer science, the CAP theorem, also known as Brewer’s theorem states that it is impossible for a distributed computer system to simultaneously provide all three of the following guarantees:

Consistency: All nodes see the same data at the same time.

Availability: A guarantee that every request receives
a response about whether it was successful or failed.

Partition Tolerance: The system continues to operate despite arbitrary message loss or failure of part of the system.

According to the theorm, a distributed system can satisfy any two of these guarantees at the same time, but not all three.Openstack Object Storgage (Swift) chose availability and partition tolerance and dropped consistency. That means that you’ll always get your data, they will be dispersed on many places, but you could get an old version of them (or no data at all) in some odd cases (like some server overload or failure). This compromise is made to allow maximum availability and scalability of the storage platform.


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