Why Local-First Apps Haven’t Become Popular? Overview Offline-first, or local-first apps, promise instant loading, improved privacy, and usability with flaky or no internet connections. However, very few apps truly implement robust offline support. Most only queue changes locally and attempt to push them when online, often resulting in unreliable syncing and loss of data, with users encountering warnings like “changes may not be saved.” The core challenge lies in syncing data correctly across multiple devices in a distributed system. --- Key Challenges in Local-First Apps Unreliable Ordering Changes happen independently on multiple devices, potentially offline, causing inconsistent states. For example: Device A sets x = 3. Device B sets x = 5. When synced, which update applies first affects the final result. Traditional databases ensure strong consistency with centralized coordination, which is too slow and brittle for local-first apps. Instead, local-first apps rely on eventual consistency, where devices converge to the same state eventually but apply changes independently. Solution: Hybrid Logical Clocks (HLCs) Combine physical time (machine clock) and logical time (incrementing counter). Timestamps generated are: Comparable (sortable), Causally consistent (encode event order). Example: Machine A records event at 10:00:00.100, HLC = (10:00:00.100, 0). Machine B’s clock at 10:00:00.095 but when receiving A’s event, advances its HLC to (10:00:00.100, 1). This ensures consistent ordering despite clock skew. --- Conflicts Conflicts arise when two devices modify the same data independently. Example: Initial balance: 100. Device A adds 20 → 120. Device B subtracts 20 → 80. Which balance to keep? Applying changes naively risks overwriting and losing data. Solution: CRDTs (Conflict-Free Replicated Data Types) CRDTs are designed for automatic conflict resolution. Important properties: Commutativity: Order of applying changes doesn’t matter. Idempotence: Multiple applications of the same change have no additional effect. Example: Last-Write-Wins (LWW) CRDT: Each update carries a timestamp. When two updates conflict, the one with the latest timestamp is chosen. This guarantees all devices eventually converge to the same state without manual conflict resolution code. --- Why SQLite Is Ideal for Local-First Apps SQLite is: Battle-tested, Lightweight, Widely available across platforms (iOS, Android, macOS, Windows, Linux, WASM). The author’s team built a local-first framework as a SQLite extension that stores every change as a message with: Timestamp (via HLC), Dataset/table name, Row (primary key), Column, Value. Applying messages: Check the current value, If the incoming message’s timestamp is newer, overwrite, If older, ignore. This approach guarantees deterministic, convergent syncing across devices, regardless of message order. --- Why This Matters This architecture makes syncing: Reliable: Works offline for extended periods without data loss. Deterministic: Final states always converge. Minimal: Small SQLite extension, no heavy dependencies. Cross-platform: Works across many OSes and environments. --- Takeaways for Developers Stop approximating offline support with simple request queues. Embrace eventual consistency principles. Use proven distributed systems techniques: Hybrid Logical Clocks (HLCs) for ordering, CRDTs for conflict resolution. Keep implementation simple and dependency-free. Result: Apps that are instant, offline-capable, private, and sync seamlessly. --- For a production-ready, cross-platform offline-first engine for SQLite, see the open-source project: SQLite-Sync.