Bigger Isn't Better for Connection Pools
A common misconception when sizing a database connection pool is "bigger is safer." But every connection occupies memory and CPU context on the database server, so an oversized pool can actually hurt database performance. The most practical way to find the right size is applying Little's Law.
Little's Law approximates the average concurrent connections needed at any moment as "requests per second × average processing time." This calculator takes your requests per second (RPS) and average query time, calculates that base figure, then adds a safety margin for traffic variance to produce a final recommended pool size. For example, at 100 requests per second and a 20ms query time, the theoretical need is just 2 concurrent connections — the safety margin accounts for real-world traffic fluctuation.
For reference, well-known connection pool libraries like HikariCP also offer a hardware-based formula: "CPU core count × 2 + effective disk spindle count." It's worth cross-checking both approaches to find a size that fits your traffic pattern and server specs. Once you've set a pool size, it's safest to monitor connection wait time and utilization metrics in production and adjust as needed.
FAQ
No. An unnecessarily large pool wastes database server resources and can actually degrade overall performance.
A common reference is 20-30% for services with high traffic variance and 10-15% for stable, predictable services.
The core-based formula reflects hardware limits, while this calculator is based on actual traffic patterns — the two approaches complement each other.