akka-reservations
Reservation is a mechanism to control the execution of I-offenders (operations that may break invariants when executed concurrently) without breaking invariants.
Motivation
Sometimes convergence is not enough. Sometimes, even if we ensure convergence with CRDTs, the invariants of applications are not preserved under weak consistency.
Welcome Invariant Preserving CRDTs (BoundedCounter, Multi-Level lock)
- They provide invariants on datatype level.
- Replicas can trade their own units but cannot touch the other replica units.
Key ideas:
- Operations are executed locally without coordination most of the time. The coordination can be moved outside the execution path in many cases.
- Successful operations guarantee the invariants to be maintained.
- When no units are available on the local replica, the algorithm fetches them from a remote replica.
- Proactive reservation mechanisms transfer resources in the background to guarantee low latency for the majority of operations.