Crate kevy_replicate 

kevy-replicate — primary-to-replica streaming replication.

Phase 1 of the v3-cluster series: one primary streams every applied mutation to N read replicas over a long-lived TCP connection, using a RESP3-extended frame format with an offset envelope. New replicas join via an inline snapshot ship, then catch up from the live frame stream.

• wire — RESP-based frame format (see docs/wire.md).
• source — primary-side bounded backlog indexed by offset.
• handshake — REPLICATE FROM <offset> ID <id> parse + +ACK format.
• slot — per-replica state + reconnect-window expiry.
• replica — replica-side blocking TCP client (handshake + frame-decoding iterator). Snapshot-ship modules land in subsequent tasks of plan .claude/plans/2026-06-18-v3-cluster-plan.md.

Applying replicated frames (T1.19)

ReplicaClient yields decoded (offset, Argv) tuples; applying them to a local store is the caller’s responsibility — the right dispatcher depends on where the replica’s data lives. The wire format intentionally carries the exact RESP argv the primary applied, so any dispatcher that hands Argv through Redis-verb routing produces a byte-equivalent local store.

The canonical in-process recipe — drop into a fresh kevy::KeyspaceStore and call kevy::dispatch:

use kevy_replicate::replica::ReplicaClient;
let mut client = ReplicaClient::connect(("primary:16004"), "replica-a", 0)?;
let mut store = kevy::KeyspaceStore::new();
for result in &mut client {
    let frame = result?;
    kevy::dispatch(&mut store, &frame.argv);
}

See the replica_apply_dispatch_mirrors_primary_store integration test in crates/kevy/tests/replication.rs for the pattern under the full primary+replica end-to-end harness.

Full server-as-replica mode (the kevy binary auto-spawns a per-shard ReplicaClient when [replication] role = "replica", routing frames into the reactor via the cross-shard ring with re-replication suppression) is Phase 1.F work (T1.28-30). v1.18.0 supports the in-process recipe above for any user that wants to drive replication themselves.

Modules

handshake

Replication handshake — the first round-trip a replica makes against the primary’s replication TCP listener.

replica

Replica-side client — connect to a primary’s replication listener, perform the handshake, then yield decoded mutation frames in order.

slot

Per-replica slot bookkeeping for the primary’s streaming loop.

source

Primary-side replication source — bounded backlog of recent mutations, indexed by monotonic offset.

wire

Wire format for replicated mutations — see docs/wire.md for the full spec.