Phase 4: Offline Data Management & Conflict Resolution #68
Description
🔄 Goal
Implement robust offline data management with conflict resolution strategies to ensure data integrity and seamless synchronization when connectivity is restored.
📋 Core Features
1. Optimistic UI Updates
Purpose: Provide instant feedback for user actions, even when offline
Tasks:
- Implement optimistic update pattern for all mutations
- Show pending state in UI during sync
- Rollback UI on sync failure
- Add visual indicators for pending operations
- Test optimistic updates across all features
Example Flow:
User action → Update UI immediately → Queue sync → Show pending badge
→ Sync when online → Confirm or rollback
2. Conflict Detection
Purpose: Identify when local and remote data diverge
Tasks:
- Implement version tracking for entities
- Detect conflicts during sync
- Store conflict metadata (timestamps, user, changes)
- Add conflict markers in data structures
- Create conflict detection algorithm
Conflict Types:
- Update-Update: Same entity modified offline and online
- Delete-Update: Entity deleted online but modified offline
- Create-Create: Duplicate creation with different IDs
3. Conflict Resolution Strategies
Purpose: Resolve data conflicts automatically or with user input
Tasks:
- Last-Write-Wins (LWW): Timestamp-based resolution
- Manual Resolution: User chooses which version to keep
- Merge Strategy: Combine non-conflicting fields
- Custom Resolvers: Per-entity-type resolution logic
- Create conflict resolution UI
- Test all resolution strategies
Resolution UI:
┌─────────────────────────────────────┐
│ 🔀 Conflict Detected │
├─────────────────────────────────────┤
│ Local Version (Offline Changes) │
│ ├─ Field1: "Value A" │
│ ├─ Field2: "Value B" │
│ └─ Modified: 2h ago │
│ │
│ Remote Version (Server) │
│ ├─ Field1: "Value X" │
│ ├─ Field2: "Value B" │
│ └─ Modified: 1h ago │
│ │
│ [Keep Local] [Keep Remote] [Merge] │
└─────────────────────────────────────┘
4. Sync Queue with Retry Logic
Purpose: Reliably sync operations with intelligent retry
Tasks:
- Implement priority queue for sync operations
- Add exponential backoff for failed syncs
- Dead letter queue for persistent failures
- Sync operation logging
- Batch sync for efficiency
- Test retry under various network conditions
Retry Strategy:
Attempt 1: Immediate
Attempt 2: 5s delay
Attempt 3: 30s delay
Attempt 4: 2m delay
Attempt 5: 10m delay
→ Move to dead letter queue
5. Data Versioning
Purpose: Track data changes for history and conflict resolution
Tasks:
- Add version field to all entities
- Implement vector clocks or hybrid logical clocks
- Store change history in IndexedDB
- Provide version diff functionality
- Implement data rollback capability
Version Structure:
interface VersionedEntity {
id: string;
version: number;
lastModified: Date;
modifiedBy: string;
changeHistory: Change[];
data: any;
}6. Migration Strategies
Purpose: Handle schema changes without data loss
Tasks:
- Define migration framework
- Version database schema
- Implement migration functions
- Test migrations with real data
- Add migration rollback capability
7. UI Indicators
Purpose: Keep users informed about sync status
Tasks:
- Sync status badge (synced, pending, failed)
- Operation counter (X pending operations)
- Last sync timestamp
- Conflict notification center
- Sync progress indicators
Status Icons:
- ✅ Synced
- 🔄 Syncing
- ⏳ Pending
⚠️ Conflict- ❌ Failed
8. State Persistence
Purpose: Maintain app state across sessions
Tasks:
- Save UI state to IndexedDB on changes
- Restore state on app load
- Handle partial state restoration
- Implement state migration
- Test persistence across browser restarts
🧪 Testing Strategy
Unit Tests
- Conflict detection algorithms
- Resolution strategies
- Retry logic
- Version comparison
Integration Tests
- End-to-end sync flows
- Conflict resolution workflows
- State persistence
- Migration execution
Stress Tests
- Large sync queues (1000+ operations)
- Network interruptions during sync
- Concurrent modifications
- Storage quota limits
📊 Success Metrics
- ✅ Sync Success Rate: >98% for all operations
- ✅ Conflict Rate: <5% of all syncs
- ✅ Auto-Resolution: >80% of conflicts resolved automatically
- ✅ Data Loss: 0% after conflict resolution
- ✅ Performance: <500ms for conflict detection
- ✅ User Satisfaction: >90% in offline usability survey
🔗 Related
- Epic: Epic: Progressive Web App Infrastructure #64 (Progressive Web App Infrastructure)
- Previous Phases: Phase 1: PWA Offline-First Foundation #65 (Phase 1), Phase 2: Multi-Language Support with Translation.io #66 (Phase 2), Phase 3: Advanced PWA Features #67 (Phase 3)
- Dependencies: Phase 3 IndexedDB and Background Sync
📚 Resources
- Offline First
- CRDTs for Conflict Resolution
- Automerge - CRDT library
- PouchDB - Offline-first database with sync
- RxDB - Reactive database with conflict handling
- Vector Clocks Explained
✅ Acceptance Criteria
- Optimistic UI updates for all mutations
- Conflict detection working reliably
- Multiple conflict resolution strategies implemented
- Sync queue with exponential backoff retry
- Data versioning and change history
- Schema migration framework
- UI indicators for all sync states
- State persistence across sessions
- Comprehensive error handling
- All tests passing (unit, integration, stress)
- Documentation complete
- User guide for conflict resolution
Type: Sub-Issue of Epic #64
Priority: High
Estimated Effort: 3-4 weeks
Dependencies:
- Phase 1 ✅ Complete
- Phase 3 (IndexedDB, Background Sync)