Database Connection Pool Manager

Database Connection Pool Manager

Optimize database connection pools for throughput, latency, and resource efficiency using PgBouncer, application-level poolers, and cloud-managed pools.

Activation Triggers

Activate on: "connection pool", "PgBouncer", "database connections", "pool size", "connection limit", "too many connections", "connection timeout", "Prisma pool", "Supabase pooler"

NOT for: SQL query optimization → data-warehouse-optimizer | Schema design → dimensional-modeler | ORM selection → api-architect

Quick Start

1. Audit current connections — SELECT count(*) FROM pg_stat_activity to understand baseline
2. Choose pooling mode — transaction pooling (default), session pooling (for prepared statements)
3. Size the pool — start with connections = (cores * 2) + spindle_count per PostgreSQL docs
4. Deploy pooler — PgBouncer sidecar or Supabase/Neon built-in pooler
5. Monitor — track active/idle/waiting connections, query queue time

Core Capabilities

Architecture Patterns

PgBouncer Transaction Pooling

App Instances (100 connections)
    ↓
PgBouncer (pool_mode = transaction)
    max_client_conn = 200
    default_pool_size = 20
    reserve_pool_size = 5
    ↓
PostgreSQL (max_connections = 30)

Key: 200 app connections share 20 actual database connections. Each connection is released back to the pool at transaction end.

Pool Sizing Formula

Optimal pool size = ((core_count * 2) + effective_spindle_count)

Example (8-core server, SSD):
  pool_size = (8 * 2) + 1 = 17

For serverless (many short-lived functions):
  pgbouncer.default_pool_size = 20
  pgbouncer.min_pool_size = 5
  app.max_pool_size = 5  (per function instance)
  total_functions * 5 <= pgbouncer.max_client_conn

Prisma with PgBouncer

// schema.prisma — pgbouncer mode disables prepared statements
datasource db {
  provider  = "postgresql"
  url       = env("DATABASE_URL")        // pooler:6543/db?pgbouncer=true
  directUrl = env("DIRECT_DATABASE_URL") // direct:5432/db (for migrations)
}

// Connection limit per Prisma instance
generator client {
  provider = "prisma-client-js"
}

// At runtime
const prisma = new PrismaClient({
  datasources: {
    db: { url: process.env.DATABASE_URL },
  },
  // connection_limit set via URL param: ?connection_limit=5
});

Anti-Patterns

1. One connection per request — never open/close connections per HTTP request; use a pool
2. Oversized pools — more connections != more throughput; past the optimal size, context switching kills performance
3. Session pooling by default — use transaction pooling unless you need prepared statements or session variables
4. No connection timeout — always set idle_timeout and server_idle_timeout to reclaim stale connections
5. Ignoring pool exhaustion — monitor cl_waiting in PgBouncer; if clients wait, pool is undersized or queries are too slow

Quality Checklist

• Pool size calculated based on CPU cores, not arbitrary numbers
• PgBouncer or equivalent deployed for serverless/high-connection workloads
• Transaction pooling mode used (session pooling only when required)
• idle_timeout set to reclaim unused connections (default: 300s)
• Application connection_limit per instance is <= pool_size / instance_count
• Migrations run on direct connection, not through pooler
• Connection pool metrics exported (active, idle, waiting, total)
• Alert configured for pool exhaustion (waiting > 0 for > 10s)
• Prepared statements disabled when using transaction pooling
• Load tested: pool handles 2x expected concurrent connections