How to fix P2024: Timed out fetching a new connection from the connection pool. Please consider reducing the number of requests or increasing the `connection_limit` parameter in Prisma

# .env
DATABASE_URL="postgresql://user:password@host:5432/db?connection_limit=10"

# AWS Lambda / Vercel Functions - start with 1-3
DATABASE_URL="postgresql://user:password@host:5432/db?connection_limit=3"

# Traditional server with 8 CPUs: default is 17 (8*2+1)
# Increase to 25 if needed
DATABASE_URL="postgresql://user:password@host:5432/db?connection_limit=25"

# Default is 10 seconds, increase to 20
DATABASE_URL="postgresql://user:password@host:5432/db?pool_timeout=20"

DATABASE_URL="postgresql://user:password@host:5432/db?connection_limit=10&pool_timeout=15"

// If you have 50 items and connection_limit=10, this will fail
const results = await Promise.all(
  items.map(item => prisma.order.findUnique({ where: { id: item.id } }))
);

// Process in batches of 5
const chunkSize = 5;
const results = [];

for (let i = 0; i < items.length; i += chunkSize) {
  const chunk = items.slice(i, i + chunkSize);
  const chunkResults = await Promise.all(
    chunk.map(item => prisma.order.findUnique({ where: { id: item.id } }))
  );
  results.push(...chunkResults);
}

// One query uses one connection
const results = await prisma.order.findMany({
  where: { id: { in: items.map(i => i.id) } }
});

# Add pgbouncer=true to disable prepared statements
DATABASE_URL="postgresql://user:password@pgbouncer:6432/db?pgbouncer=true&connection_limit=1"

# Use Supabase's transaction pooler URL
DATABASE_URL="postgresql://user:[email protected]:6543/db?pgbouncer=true"

DATABASE_URL="postgresql://user:[email protected]:5432/db"

// Creates new client + pool every time
export async function handler(event) {
  const prisma = new PrismaClient();
  const data = await prisma.user.findMany();
  await prisma.$disconnect(); // DON'T do this in serverless
  return data;
}

// Reuse client across warm starts
const prisma = new PrismaClient({
  datasources: {
    db: { url: process.env.DATABASE_URL }
  }
});

export async function handler(event) {
  const data = await prisma.user.findMany();
  // Don't disconnect - reuse the connection
  return data;
}

aws lambda put-function-concurrency \
  --function-name my-function \
  --reserved-concurrent-executions 10

{
  "functions": {
    "api/**/*.ts": {
      "maxDuration": 10,
      "memory": 1024
    }
  }
}