Database Connection Pooling

You are a database connection expert. Help me configure connection pooling.

## Environment Details
Database: ${{DATABASE}}
Application type: ${{APP_TYPE}}
Concurrent users: ${{USERS}}
Serverless: ${{SERVERLESS}}

## Please Configure:

1. **Pool Sizing**

// Formula considerations:
// connections = (core_count * 2) + spindle_count
// Adjust for:
// - Transaction duration
// - Query complexity
// - Concurrent requests
// - Memory per connection


2. **PgBouncer Setup**

# pgbouncer.ini
[databases]
mydb = host=localhost dbname=mydb

[pgbouncer]
pool_mode = transaction
max_client_conn = 1000
default_pool_size = 25
min_pool_size = 5
reserve_pool_size = 5
reserve_pool_timeout = 3


3. **Pool Modes**

// Mode selection:
// Session pooling - Full session, most compatible
// Transaction pooling - Per transaction, most efficient
// Statement pooling - Per statement, limited use


4. **Application Pool**

// Node.js pg pool:
const pool = new Pool({
  max: 20,
  min: 5,
  idleTimeoutMillis: 30000,
  connectionTimeoutMillis: 2000,
  maxUses: 7500
});


5. **Serverless Considerations**

// Serverless challenges:
// - Connection exhaustion
// - Cold start connections
// Solutions:
// - RDS Proxy
// - PlanetScale
// - Connection string pooling


6. **Monitoring**

-- Pool monitoring:
SHOW POOLS;
SHOW CLIENTS;
SHOW SERVERS;
SHOW STATS;

-- PostgreSQL connections:
SELECT * FROM pg_stat_activity;


7. **Timeout Configuration**

# Timeout settings:
query_timeout = 300
client_idle_timeout = 60
server_connect_timeout = 3
server_idle_timeout = 60


8. **High Availability**

# HA configuration:
# - Multiple backends
# - Health checks
# - Failover