Electric — Postgres Sync Engine for Local-First Apps

Introduction

Electric is a Postgres sync engine that streams real-time data changes from your database into client applications. It uses a concept called Shapes to define partial replicas of your data, and delivers them through an HTTP API designed to work with CDNs for scalable fan-out.

What Electric Does

• Streams real-time change data from Postgres tables to any HTTP client
• Supports partial replication using Shapes that filter by table, columns, and where clauses
• Delivers data over a simple HTTP API compatible with CDNs and edge caching
• Provides client libraries for React, TypeScript, and Elixir with reactive data hooks
• Maintains causal consistency guarantees for synced data subsets

Architecture Overview

Electric connects to Postgres via logical replication and consumes the WAL (write-ahead log) to track data changes. It maintains an internal shape log that partitions changes by shape definition. Clients subscribe to shapes over HTTP using long-polling or streaming responses. The HTTP protocol is designed so that CDNs can cache and serve shape responses, reducing load on the Electric service for high fan-out scenarios.

Self-Hosting & Configuration

• Deploy Electric as a Docker container or standalone binary alongside your Postgres instance
• Set the DATABASE_URL environment variable pointing to your Postgres database
• Enable logical replication on your Postgres (wal_level = logical)
• Define shapes via query parameters on the HTTP API (table, columns, where)
• Place a CDN in front of the Electric HTTP endpoint for production-scale delivery

Key Features

• Shape-based sync: clients subscribe to exactly the data subset they need
• CDN-compatible: HTTP responses use standard cache headers for edge delivery
• Framework integrations: useShape() hooks for React and helpers for other frameworks
• Incremental sync: clients receive only the changes since their last sync offset
• No vendor lock-in: uses standard Postgres logical replication with no database extensions required

Comparison with Similar Tools

• Supabase Realtime — WebSocket-based change notifications; Electric provides full data sync with offline support
• Firebase — proprietary real-time database; Electric syncs from your own Postgres
• PowerSync — Postgres sync to SQLite; Electric syncs to any client without requiring SQLite
• Liveblocks — real-time collaboration primitives; Electric is a general-purpose data sync layer
• Debezium — CDC pipeline for backend services; Electric is optimized for client-facing partial replication

FAQ

Q: Does Electric require changes to my Postgres schema? A: No. Electric reads from standard Postgres tables via logical replication. No extensions, triggers, or schema modifications are needed.

Q: Can clients work offline? A: Yes. Client libraries cache synced shapes locally. When the connection resumes, Electric sends only the changes that occurred while offline.

Q: How does Electric handle write conflicts? A: Electric is a read-path sync engine. Writes go directly to Postgres through your application API. If you need conflict resolution for offline writes, you implement that logic in your application layer.

Q: What scale can Electric handle? A: The HTTP/CDN architecture allows horizontal fan-out to many clients. A single Electric instance handles the Postgres connection, while CDN edges serve cached shape responses.

Sources

• https://github.com/electric-sql/electric
• https://electric-sql.com/docs