Database

Teaches Conflict-free Replicated Data Types (CRDTs), the mathematical foundation for local-first sync. Covers how CRDTs guarantee eventual consistency without coordination, the difference between state-based and operation-based CRDTs, and practical implementations of G-Counter, PN-Counter, LWW-Register, OR-Set, G-Set, and RGA (Replicated Growable Array). Includes causal ordering, vector clocks, and guidance on choosing the right CRDT for your data model.

Teaches ElectricSQL, a Postgres-backed local-first sync framework. Covers the Electric architecture where Postgres is the source of truth and data syncs to local SQLite databases on client devices via shape-based partial replication. Includes shape definitions, live queries, offline-first patterns, conflict resolution with rich CRDTs, integration with React and Expo (React Native), deployment patterns, and migration strategies.

Teaches IndexedDB patterns for local-first web applications, using Dexie.js as the primary wrapper library. Covers schema design and versioning, creating indexes for efficient queries, transaction patterns, performance optimization (bulk operations, pagination, lazy loading), migration strategies for schema evolution, storage quota management, data export and import, and integration patterns with sync engines and reactive frameworks.

Teaches authentication and authorization patterns for local-first applications that must work offline. Covers offline-capable auth with cached tokens, permission sync and local enforcement, encrypted local storage for sensitive data, key management with device-bound keys, device authorization and revocation, multi-device identity linking, end-to-end encryption for synced data, and secure patterns for handling auth in disconnected environments.

Teaches the local-first software paradigm where applications store data on the user's device, work fully offline, and sync to peers or servers when connectivity is available. Covers the spectrum from cloud-first to offline-first to local-first, core benefits (instant UX, offline capability, data ownership, privacy), key challenges (conflict resolution, sync complexity, storage limits), architectural patterns, and decision frameworks for when local-first is the right choice.

Teaches how to design and build a sync engine for local-first applications. Covers the operation log as the foundation, conflict resolution strategies (last-write-wins, operational transform, CRDTs), server reconciliation patterns, partial sync for large datasets, bandwidth optimization techniques, version vectors and causal consistency, clock synchronization, and practical implementation patterns with code examples.

Teaches building local-first collaborative applications with Yjs, the most widely adopted CRDT library for JavaScript. Covers the Y.Doc document model, shared types (Y.Map, Y.Array, Y.Text, Y.XmlFragment), the awareness protocol for presence and cursors, persistence and sync providers (WebSocket, WebRTC, IndexedDB), integrating with editors like ProseMirror/TipTap/CodeMirror/Monaco, undo/redo management, and performance optimization patterns.

Teaches Zero (by Rocicorp), the successor to Replicache, a sync engine for building local-first web applications with instant UI, optimistic mutations, and server-side authority. Covers the Zero architecture (client cache, sync engine, server), defining queries and mutators, the reactivity model, server-side authorization and permissions, optimistic updates with automatic rollback, deployment patterns, and migration from Replicache.