Offline-First SQLite with PowerSync & ElectricSQL: Instant Reactive Mobile Sync

Users expect mobile apps to work instantly on the subway, in rural job sites, and during airplane flights. Traditional web architecture requires waiting for an API call before updating the screen. Local-first architecture stores data in an embedded on-device SQLite database, rendering reads in 0ms and streaming mutations to PostgreSQL in the background via replication streams.

Architectural Takeaways

• In a local-first application, all reads and writes execute against local on-device SQLite, delivering instantaneous 0ms UI responsiveness.
• PowerSync and ElectricSQL stream partial PostgreSQL replication changes directly to client SQLite databases based on tenant permissions.
• Last-Write-Wins (LWW) and Conflict-Free Replicated Data Types (CRDTs) resolve conflicting offline edits automatically without corrupting state.

1. The Local-First Software Manifesto: Speed & Sovereignty

Local-first software treats the device database as the primary source of truth, treating the cloud as a synchronization and backup relay. Apps open instantly without loading spinners.

2. Setting Up PowerSync with React Native & PostgreSQL

PowerSync syncs PostgreSQL tables directly into client SQLite databases using declarative sync rules defined in YAML.

3. Resolving Concurrent Offline Sync Conflicts

Hybrid Logical Clocks assign monotonically increasing timestamps that combine physical wall-clock time with logical sequence counters, ensuring fair conflict resolution.

4. Mobile Storage Quotas & Partial Sync Buckets

Sync rules ensure mobile devices sync only active projects belonging to the logged-in user rather than the entire corporate database.

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