This trace follows the actual state transitions behind the companion Replication Improves Availability at a Consistency Cost. It describes a common execution path; implementation details can vary, so keep the contract separate from the mechanism.
Step 1: Accept a write at an owner
Replication stores copies of data on multiple machines to improve availability, read capacity, or recovery. The system must define how writes reach replicas and what reads are allowed to observe. “Consistent” is not one universal behavior; the contract should name ordering and freshness guarantees.
Step 2: Propagate it to replicas
With asynchronous replication, a write can be acknowledged by the leader before a follower receives it, so an immediate read from that follower may return an older value. Read-your-writes can be supported by routing a client to an up-to-date replica or carrying a version constraint.
Step 3: Apply the acknowledgement rule
An asynchronously updated replica can serve an older version after the leader acknowledges a write; route to a sufficiently fresh copy when the product promises read-your-writes.
At this point, record the state that changed and check the invariant before advancing. If the operation repeats, make clear which values persist and which are recomputed.
Step 4: Serve a subsequent read
Synchronous replication can reduce the window of acknowledged data loss but may add latency or reduce write availability when a replica is unreachable. A quorum is meaningful only with a defined membership and failure model. Replicas do not replace backups against accidental deletion or corruption.
Step 5: Enforce the freshness contract
A user updates an address and then reads the previous address from another region. State which consistency promise is missing and one routing or replication strategy that can provide it.
The trace is complete when the result satisfies the stated contract. Compare this model with the concrete runtime or system you are studying before making a performance claim.