Offline Sync Engine
Building a robust offline-first data synchronization engine with conflict resolution for mobile apps.
Why I Built This
Tech Stack
Technical Approach
Started with research on existing solutions like WatermelonDB and Realm, then built a custom solution tailored for Flutter apps.
Architecture Design
Designed a queue-based sync system with versioning and conflict detection.
Local Storage Layer
Built SQLite wrapper with automatic schema migrations and type-safe queries.
Sync Queue Implementation
Created a priority queue for pending operations with retry logic and exponential backoff.
Conflict Resolution
Implemented last-write-wins and custom merge strategies for different data types.
Key Learnings
What worked, what didn't, and what I'd do differently.
What Worked
- Queue-based sync with timestamps ensures no data loss
- Optimistic UI updates make the app feel responsive
- Batch sync operations reduce API calls significantly
Challenges Faced
- Initial simple timestamp comparison missed edge cases
- Large sync payloads caused memory issues — needed chunking
Key Insights
The bigger lessons that go beyond this specific experiment.
Offline First is Complex
There's no one-size-fits-all solution. Each app needs customized conflict resolution strategies.
UX Matters Most
Users don't care about sync — they care that their data is always available and up-to-date.
Test Everything
Network simulation testing is essential. Real-world conditions are unpredictable.