Cloudflare D1 Primer

What is D1?

D1 is Cloudflare's serverless SQL database built on SQLite. Every database is replicated across Cloudflare's global network. Reads hit the nearest replica in single-digit milliseconds. Writes route through a primary and propagate automatically.

Why D1 over alternatives?

• No connection pooling. Workers connect via HTTP API — no TCP exhaustion.
• SQLite dialect. Full SQL, indexes, triggers, views. Familiar tooling.
• Row-based billing. Pay for rows read/written, not compute hours.
• Wrangler-native. Migrations, backups, and branching built into the CLI.

Quick start

npx wrangler d1 create meridian-db
npx wrangler d1 execute meridian-db --file=./schema.sql

Schema file contains standard CREATE TABLE statements. Wrangler applies them transactionally.

Worker binding

export default {
  async fetch(req, env) {
    const { results } = await env.DB
      .prepare("SELECT * FROM users WHERE id = ?")
      .bind(userId)
      .all()
    return Response.json(results)
  }
}

Limits to know

• 10 GB max per database.
• 100 MB max per row.
• Writes per database: 1,000/second (burst).
• Bound parameters capped at 100 per query.