Database Connection Pool Exhausted Error

Configure a larger pool size based on your expected concurrency.

// Prisma
const prisma = new PrismaClient({
  datasources: { db: { url: process.env.DATABASE_URL } },
  // connection_limit defaults to num_cpus * 2 + 1
})

// node-postgres
const { Pool } = require("pg")
const pool = new Pool({
  max: 20, // maximum connections in pool
  idleTimeoutMillis: 30000,
  connectionTimeoutMillis: 5000,
})

Configure idle timeout to release unused connections.

// Prisma: set connection limit in datasource
datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL")
  // connection_limit = 10
}

// PostgreSQL: set statement timeout
ALTER DATABASE mydb SET statement_timeout = '30s';

Check how many connections are active and what queries are running.

-- PostgreSQL: check active connections
SELECT pid, state, query_start, query
FROM pg_stat_activity
WHERE state = 'active'
ORDER BY query_start DESC;

-- Check total connections
SELECT count(*) FROM pg_stat_activity;

-- Kill idle connections
SELECT pg_terminate_backend(pid)
FROM pg_stat_activity
WHERE state = 'idle'
AND query_start < NOW() - INTERVAL '5 minutes';