Je cite:

"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 theorem, a distributed system cannot satisfy all three of these guarantees at the same time."