Database pools

A database pool keeps warm connections to a Postgres or MySQL database near your app, so each request skips the TCP, TLS, and login round trips of opening a new connection. It can also cache read queries for a short time. Pools matter most for SSR and hybrid apps running as Workers, which open a fresh connection on every request. The pool points at a database you already have: this app's dply database, or any Postgres or MySQL reachable from the internet, such as Neon, Supabase, RDS, or PlanetScale.

Create a pool#

1. In your app, open Overview.
2. Choose Add resource, then Database pool.
3. Leave Create new selected and enter a Name, such as DB.
4. Choose what to pool:
   • This app's database pools the dply Postgres or MySQL the app already has. This option only appears when the app has one.
   • Another database: paste its Address, for example postgres://user:secret@db.example.com:5432/app. The address must include a user, password, host, and database name, and start with postgres://, postgresql://, or mysql://.
5. Choose Create, then deploy the app.

Creating a pool connects to the database once, which can take a few seconds if it is waking up. The pasted address is sent to the pool and is not stored or shown by dply.

To reuse a pool this organization already created, choose Attach existing and pick it from Existing Pool.

Use the pool#

SSR and hybrid apps (Workers)#

The next deploy binds the pool as env.<NAME>, where <NAME> is the name you gave it in capitals. Pass its connectionString to your usual driver. Workers need the nodejs_compat compatibility flag.

import { Client } from 'pg';

export default {
  async fetch(request, env, ctx) {
    const client = new Client({ connectionString: env.DB.connectionString });
    await client.connect();
    const { rows } = await client.query('select now()');
    ctx.waitUntil(client.end());
    return Response.json(rows);
  },
};

With postgres.js:

import postgres from 'postgres';

const sql = postgres(env.DB.connectionString, { max: 5, fetch_types: false });
const rows = await sql`select now()`;
ctx.waitUntil(sql.end());

Container apps#

A container app reads the pool's connection string from its private host after the next deploy. The host is shown on the pool's Connect tab.

$url = Http::get('http://dply.<app>.db.internal/')->json('connectionString');

const { connectionString } = await (await fetch('http://dply.<app>.db.internal/')).json();

Inspect the pool#

Choose Open on the pool card. The Overview tab shows the database host, database, user, engine, and whether query caching is on. The Settings tab shows the pool id.

Pricing#

dply does not bill pools separately. You pay for the database the pool points at.

Delete a pool#

On the pool's Settings tab, choose Delete, then Delete resource. If this organization created the pool, it is deleted; otherwise it is only detached from this app. The database it points at, and its data, are not touched.

If a live deploy still uses the pool, the delete waits until the next deploy drops it, so the running app does not break. Detach on the card removes the pool from this app and keeps it for other apps.

Related#

• Postgres, MySQL & MongoDB
• Server rendering (SSR)
• Environment variables