# Phase 3: Distributed Systems - Detailed Implementation (Weeks 5-6, 80 hours)

## Overview

Multi-level caching, distributed tracing, and CRDT for real-time collaboration.

## Week 1: Multi-Level Caching (40 hours)

### Day 1-2: Cache Architecture (16 hours)

**Tasks:**
1. Create `backend/internal/cache/cache.go`:
   - L1: Redis (distributed)
   - L2: In-memory (local)
   - L3: Database (persistent)

2. Implement cache layers:
   - Redis client with connection pooling
   - In-memory cache with TTL
   - Cache invalidation strategy

3. Add cache warming:
   - Preload hot data
   - Background refresh
   - Predictive loading

### Day 3-4: Cache Invalidation (16 hours)

**Tasks:**
1. Create `backend/internal/cache/invalidation.go`:
   - Event-based invalidation
   - TTL-based expiration
   - Manual invalidation
   - Cascade invalidation

2. Implement invalidation patterns:
   - Write-through
   - Write-behind
   - Write-around

3. Add monitoring:
   - Cache hit rate
   - Cache miss rate
   - Eviction rate

### Day 5: Testing & Optimization (8 hours)

**Tasks:**
1. Write cache tests
2. Test invalidation
3. Performance testing
4. Optimize hit rates
5. Monitor metrics

## Week 2: Distributed Tracing & CRDT (40 hours)

### Day 1-2: Distributed Tracing (16 hours)

**Tasks:**
1. Setup Jaeger integration:
   - Create `backend/internal/tracing/tracing.go`
   - Initialize Jaeger client
   - Configure sampling

2. Add OpenTelemetry instrumentation:
   - Trace all HTTP requests
   - Trace database queries
   - Trace cache operations
   - Trace external API calls

3. Create custom spans:
   - Business logic spans
   - Performance metrics
   - Error tracking

### Day 3-4: CRDT Implementation (16 hours)

**Tasks:**
1. Create `backend/internal/crdt/crdt.go`:
   - CRDT for requirement descriptions
   - Conflict-free merging
   - Operational transformation

2. Implement real-time sync:
   - WebSocket updates
   - Offline support
   - Sync on reconnect

3. Add conflict resolution:
   - Last-write-wins
   - Vector clocks
   - Causal ordering

### Day 5: Integration & Testing (8 hours)

**Tasks:**
1. Integrate tracing with handlers
2. Integrate CRDT with WebSocket
3. Write integration tests
4. Test performance
5. Test offline scenarios

## Implementation Details

### Cache Layer Structure

```go
type CacheLayer struct {
    L1 *redis.Client      // Distributed
    L2 *ristretto.Cache   // In-memory
    L3 *pgxpool.Pool      // Database
}

func (c *CacheLayer) Get(ctx context.Context, key string) (interface{}, error) {
    // Try L1 (Redis)
    // Try L2 (In-memory)
    // Try L3 (Database)
    // Populate L1 and L2
}
```

### Tracing Configuration

```go
type TracingConfig struct {
    ServiceName string
    JaegerURL   string
    SamplingRate float64
}

func InitTracing(cfg TracingConfig) (*trace.TracerProvider, error) {
    // Setup Jaeger exporter
    // Create tracer provider
    // Set global tracer
}
```

### CRDT Operations

```go
type CRDT struct {
    ID        string
    Content   string
    Timestamp int64
    UserID    string
    VectorClock map[string]int
}

func (c *CRDT) Merge(other *CRDT) *CRDT {
    // Merge two CRDT states
    // Resolve conflicts
    // Return merged state
}
```

## Success Criteria

✅ Multi-level caching working
✅ Cache hit rate >80%
✅ Distributed tracing working
✅ CRDT sync working
✅ Offline support working
✅ All tests passing

## Expected Results

- **Performance:** 10x faster queries
- **Latency:** <50ms for cached queries
- **Visibility:** Complete request tracing
- **Collaboration:** Real-time sync with conflict resolution

## Troubleshooting

**Issue:** Cache inconsistency
- Check invalidation logic
- Check TTL settings
- Rebuild cache

**Issue:** Tracing overhead
- Adjust sampling rate
- Check span creation
- Optimize instrumentation

**Issue:** CRDT conflicts
- Check vector clocks
- Check merge logic
- Review conflict resolution

## Next Phase

After Phase 3 complete:
- Move to Phase 4: Security & Zero Trust
- Implement fine-grained access control
- Add encryption

