# Implementation Plan: Distributed KVS Consistency Modes

**Branch**: `003-kvs-consistency` | **Date**: 2025-12-01 | **Spec**: specs/003-kvs-consistency/spec.md  
**Input**: Feature specification from `/specs/003-kvs-consistency/spec.md`

**Note**: This template is filled in by the `/speckit.plan` command. See `.specify/templates/commands/plan.md` for the execution workflow.

## Summary

Deliver a deployable distributed KVS supporting strong consistency (quorum read/write) and eventual consistency (LWW default), with namespace-level mode selection, safe mode switching, convergence/recovery behavior, and observability.

## Technical Context

**Language/Version**: Rust (stable, via Nix flake)  
**Primary Dependencies**: raft-rs, tonic/prost gRPC, RocksDB, tokio  
**Storage**: RocksDB for raft log/state and KV data  
**Testing**: cargo test (unit/integration), extend rdb-server multi-node tests for namespace/mode behaviors  
**Target Platform**: Linux server (Nix dev shell)  
**Project Type**: Distributed server (rdb-server) with gRPC API/CLI  
**Performance Goals**: Strong mode quorum commit p95 ~1–2s; eventual mode convergence within a few seconds under normal network; observable lag metrics  
**Constraints**: Constitution (test-first, observability, compatibility); fixed membership scope for this phase; namespace-level mode config  
**Scale/Scope**: Small cluster (3–5 nodes) dev target; multiple namespaces with per-namespace mode

## Constitution Check

*GATE: Must pass before Phase 0 research. Re-check after Phase 1 design.*

- Test-First: Add/extend integration tests for strong/eventual modes, namespace config, convergence/recovery.  
- Reliability & Coverage: Keep existing Raft tests green; new tests cover mode behaviors and failures.  
- Simplicity & Readability: Reuse existing crates and current server structure; avoid bespoke protocols.  
- Observability: Structured logs/metrics for mode, convergence lag, quorum status, config state.  
- Versioning & Compatibility: Call out any gRPC/contract changes; fixed membership scope maintained.

## Project Structure

### Documentation (this feature)

```text
specs/003-kvs-consistency/
├── plan.md
├── research.md
├── data-model.md
├── quickstart.md
├── contracts/
└── tasks.md   # via /speckit.tasks
```

### Source Code (repository root)

```text
rdb-server/
  src/
    peer.rs
    peer_manager.rs
    raft_service.rs
    config/          # add namespace/mode config handling
    api/             # gRPC handlers (mode/config endpoints if needed)
  tests/
    test_replication.rs (extend for mode/namespace cases)

rdb-proto/
  src/*.proto        # update if API exposes mode/config

scripts/
  verify-raft.sh     # update or add mode verification script
```

**Structure Decision**: Extend existing rdb-server layout with namespace/mode config, tests under rdb-server/tests, contracts under specs/003-kvs-consistency/contracts.

## Complexity Tracking

> **Fill ONLY if Constitution Check has violations that must be justified**

| Violation | Why Needed | Simpler Alternative Rejected Because |
|-----------|------------|-------------------------------------|
| N/A | | |