Configuring Connection Pools

Always use connection_limit=1 per instance: Serverless platforms scale horizontally; total connections = instances × limit. Example: 100 Lambda instances × 1 = 100 DB connections (safe) vs. 100 × 10 = 1,000 (exhausted).

AWS Lambda / Vercel / Netlify:

DATABASE_URL="postgresql://user:pass@host:5432/db?connection_limit=1&pool_timeout=0&connect_timeout=10"

Additional optimizations:

• pool_timeout=0: Fail fast instead of waiting for connections
• connect_timeout=10: Timeout initial DB connection
• pgbouncer=true: Use PgBouncer transaction mode

PgBouncer for High Concurrency

Deploy external pooler when: >100 application instances, unpredictable serverless scaling, multiple apps sharing one database, connection exhaustion, frequent P1017 errors

Configuration:

[databases]
mydb = host=postgres.internal port=5432 dbname=production

[pgbouncer]
pool_mode = transaction
max_client_conn = 1000
default_pool_size = 20
reserve_pool_size = 5
reserve_pool_timeout = 3

**Prisma with

PgBouncer:**

DATABASE_URL="postgresql://user:pass@pgbouncer:6432/db?pgbouncer=true&connection_limit=10"

Avoid in transaction mode: Prepared statements (disabled with pgbouncer=true), persistent SET variables, LISTEN/NOTIFY, advisory locks, temporary tables

Bottleneck Identification

P1017 Error (Connection pool timeout): "Can't reach database server at localhost:5432"

Causes: connection_limit too low, slow queries holding connections, missing cleanup, database at max_connections limit

Diagnosis:

import { Prisma } from '@prisma/client';

const prisma = new Prisma.PrismaClient({
  log: [{ emit: 'event', level: 'query' }],
});

prisma.$on('query', (e) => {
  console.log('Query duration:', e.duration);
});

const metrics = await prisma.$metrics.json();
console.log('Pool metrics:', metrics);

Check pool status:

SELECT count(*) as connections, state, wait_event_type, wait_event
FROM pg_stat_activity WHERE datname = 'your_database'
GROUP BY state, wait_event_type, wait_event;

SHOW max_connections;
SELECT count(*) FROM pg_stat_activity;

Pool Configuration Parameters

Complete URL example: