How to fix Heroku: Connection limit reached in PostgreSQL

First, determine how many connections are currently open and identify what is consuming them:

# See connection stats for your database
heroku pg:info --app your-app-name

# View active connections and their sources
heroku pg:ps --app your-app-name

# Kill all connections if needed (emergency measure)
heroku pg:killall --app your-app-name

The heroku pg:ps output shows the process ID (pid), username, and query of each connection. Look for patterns: are connections from your web dynos, workers, or external tools?

The recommended solution is to use Heroku's pgBouncer add-on or connection pooling. This pools connections on the server side, allowing many application connections to share fewer database connections:

# Add pgBouncer to your Heroku app
heroku addons:create heroku-postgresql:mini -a your-app-name

# Or if pgBouncer buildpack, add the buildpack
heroku buildpacks:add https://github.com/heroku/heroku-buildpack-pgbouncer.git -a your-app-name

Once pgBouncer is enabled, update your DATABASE_URL environment variable to point to the pgBouncer instance. Heroku will provide a separate pgBouncer connection URL. This allows your app to open many logical connections to pgBouncer while pgBouncer maintains fewer actual database connections.

For Node.js with node-postgres, use a connection pool and configure pool size appropriately:

import { Pool } from 'pg';

const pool = new Pool({
  connectionString: process.env.DATABASE_URL,
  max: 10,  // Reduce from default 10 per dyno
  idleTimeoutMillis: 30000,
  connectionTimeoutMillis: 5000,
});

// Use the pool for all queries
const result = await pool.query('SELECT * FROM users');

For Prisma ORM, configure the connection string in .prisma/schema.prisma:

datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL")
  // Prisma uses a connection pool internally
  // Default pool size is 10; reduce for constrained environments
}

For other frameworks (Rails, Django, etc.), consult their documentation for connection pool configuration and keep the pool size modest (5-15 depending on dyno tier).

If you have multiple application dynos or background workers, each opening independent connections, reduce the total number:

# Scale down web dynos
heroku ps:scale web=1 -a your-app-name

# Check current process types
heroku ps -a your-app-name

# Scale specific process types
heroku ps:scale worker=0 -a your-app-name  # Disable workers if not needed

Each dyno that connects to the database consumes connections. If you have 5 web dynos with a connection pool of 10, you're using 50 connections. Consider using Heroku Scheduler for periodic tasks instead of always-running worker dynos.

Ensure all database connections are properly closed in error cases:

// Bad: connection may not close if query fails
const client = await pool.connect();
const result = await client.query('SELECT * FROM users');
client.release();

// Good: connection released even if query fails
const client = await pool.connect();
try {
  const result = await client.query('SELECT * FROM users');
} finally {
  client.release();
}

// Best: use pool.query() directly (handles cleanup automatically)
const result = await pool.query('SELECT * FROM users');

Always use try/finally or the pool's query methods directly rather than holding onto connections. In middleware-based frameworks, ensure connections opened in middleware are also closed after the response.

If you have preboot enabled, it temporarily doubles connection usage during deployments. Disable it if connection count is marginal:

# Check if preboot is enabled
heroku features -a your-app-name

# Disable preboot
heroku features:disable preboot -a your-app-name

With preboot disabled, new dynos are fully booted before old ones are terminated, but connection usage won't spike during deployment.

If you've optimized pooling and connection usage but still need more capacity, upgrade to a higher Heroku Postgres tier:

# List available plans
heroku addons:plans heroku-postgresql

# Upgrade to a larger tier (e.g., Standard-2 with 400 connections)
heroku addons:upgrade heroku-postgresql:standard-2 DATABASE -a your-app-name

Note: Heroku does not provide a way to increase connection limits on a given tier. Upgrade is the only way to get more connections. Compare the cost vs. optimizing your application's connection usage.