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98 lines
5.1 KiB
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98 lines
5.1 KiB
Text
---
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title: Real-Time Sync with Zero
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description: How SurfSense uses Rocicorp Zero for instant real-time data synchronization
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---
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# Real-Time Sync with Zero
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SurfSense uses [Rocicorp Zero](https://zero.rocicorp.dev/) for real-time data synchronization. Zero continuously replicates data from PostgreSQL to a local cache on each client, enabling instant UI updates for notifications, documents, connectors, chat messages, and comments.
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## How It Works
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Zero runs a **zero-cache** server that sits between PostgreSQL and the browser:
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1. **zero-cache** replicates data from PostgreSQL into a local SQLite replica using logical replication
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2. The browser connects to zero-cache via WebSocket and syncs relevant data locally
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3. When data changes in PostgreSQL (e.g., a new notification), zero-cache pushes the update to all connected clients instantly
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4. Queries run against local data first for instant results, then update when server data arrives
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## Architecture
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| Component | Role |
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|-----------|------|
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| **PostgreSQL** | Source of truth (with `wal_level=logical`) |
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| **zero-cache** | Replicates Postgres → SQLite, serves client sync via WebSocket |
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| **Browser** | Stores synced data locally, runs queries against local cache |
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## Configuration
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### Docker Deployment
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zero-cache is included in the Docker Compose setup. The key environment variables are:
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| Variable | Description | Default |
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|----------|-------------|---------|
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| `ZERO_CACHE_PORT` | Port for the zero-cache service | `5929` (prod) / `4848` (dev) |
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| `ZERO_ADMIN_PASSWORD` | Password for the zero-cache admin UI and `/statz` endpoint | `surfsense-zero-admin` |
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| `ZERO_UPSTREAM_DB` | PostgreSQL connection URL for replication | Built from `DB_*` vars |
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| `NEXT_PUBLIC_ZERO_CACHE_URL` | URL the frontend uses to connect to zero-cache | `http://localhost:<ZERO_CACHE_PORT>` |
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| `ZERO_APP_PUBLICATIONS` | PostgreSQL publication restricting which tables are replicated | `zero_publication` |
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| `ZERO_NUM_SYNC_WORKERS` | Number of view-sync worker processes. Must be ≤ `ZERO_UPSTREAM_MAX_CONNS` and ≤ `ZERO_CVR_MAX_CONNS` | `4` |
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| `ZERO_UPSTREAM_MAX_CONNS` | Max connections to upstream PostgreSQL for mutations | `20` |
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| `ZERO_CVR_MAX_CONNS` | Max connections to the CVR database | `30` |
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### Manual / Local Development
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If running the frontend outside Docker (e.g., `pnpm dev`), you need:
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1. A running zero-cache instance pointing at your PostgreSQL database
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2. `NEXT_PUBLIC_ZERO_CACHE_URL` set in your `.env` file (default: `http://localhost:4848`)
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### Custom Domain / Reverse Proxy
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When deploying behind a reverse proxy, set `NEXT_PUBLIC_ZERO_CACHE_URL` to your public zero-cache URL (e.g., `https://zero.yourdomain.com`). The zero-cache service must be accessible via WebSocket from the browser.
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### Database Requirements
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zero-cache connects to PostgreSQL using logical replication. The database must meet these requirements:
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1. **`wal_level = logical`** — already configured in the bundled `postgresql.conf`
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2. **The database user must have `REPLICATION` privilege** — required for creating logical replication slots
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In the default Docker setup, the `surfsense` user is a PostgreSQL superuser and has all required privileges automatically.
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**For managed databases** (RDS, Supabase, Cloud SQL, etc.) where the app user may not be a superuser, you need to grant replication privileges:
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```sql
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ALTER USER surfsense WITH REPLICATION;
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GRANT CREATE ON DATABASE surfsense TO surfsense;
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```
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The `REPLICATION` privilege allows zero-cache to create a logical replication slot for streaming changes. The `CREATE` privilege allows zero-cache to create internal schemas (`zero`, `zero_0`) for its metadata.
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## Synced Tables
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Zero syncs the following tables for real-time features:
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| Table | Used By |
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|-------|---------|
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| `notifications` | Inbox (comments, document processing, connector status) |
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| `documents` | Document list, processing status indicators |
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| `folders` | Nested folder tree for organizing documents |
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| `search_source_connectors` | Connector status, indexing progress |
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| `new_chat_messages` | Live chat message sync for shared chats |
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| `chat_comments` | Real-time comment threads on AI responses |
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| `chat_session_state` | Collaboration indicators (who is typing) |
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## Troubleshooting
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- **zero-cache not starting**: Check `docker compose logs zero-cache`. Ensure PostgreSQL has `wal_level=logical` (configured in `postgresql.conf`).
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- **"Insufficient upstream connections" error**: zero-cache defaults `ZERO_NUM_SYNC_WORKERS` to the number of CPU cores, which can exceed connection pool limits on high-core machines. Lower `ZERO_NUM_SYNC_WORKERS` or raise `ZERO_UPSTREAM_MAX_CONNS` / `ZERO_CVR_MAX_CONNS` in your `.env`.
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- **Frontend not syncing**: Open DevTools → Console and check for WebSocket connection errors. Verify `NEXT_PUBLIC_ZERO_CACHE_URL` matches the running zero-cache address.
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- **Stale data after restart**: zero-cache rebuilds its SQLite replica from PostgreSQL on startup. This may take a moment for large databases.
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## Learn More
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- [Rocicorp Zero Documentation](https://zero.rocicorp.dev/docs)
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- [Zero Schema Reference](https://zero.rocicorp.dev/docs/schema)
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- [Zero Deployment Guide](https://zero.rocicorp.dev/docs/deployment)
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