Delivery

• Delivery of messages/requests in distributed systems

• we can’t deliver messages reliably and in order in the face of network partitions and crashes without a high degree of coordination. This coordination, of course, comes at a cost (latency and availability), while still relying on at-least-once semantics.

at-most-once delivery

at-least-once delivery

• at-least-once delivery is also impossible because, technically speaking, network partitions are not strictly time-bound.

  • If the connection from you to the server is interrupted indefinitely, you can’t deliver anything.

Exactly once delivery

• impossible

  • See the two generals problem

• https://bravenewgeek.com/you-cannot-have-exactly-once-delivery/