Connection Pooling: The MySQL Performance Multiplier

Connections Are Expensive

Each MySQL connection consumes memory for its thread stack, session buffers, and sort/join buffers. At hundreds or thousands of concurrent connections, this overhead alone can exhaust server memory and trigger OOM kills, even if the queries themselves are lightweight.

ProxySQL vs Application-Level Pooling

Application-level connection pools (HikariCP, SQLAlchemy pool, etc.) reduce connection overhead within a single application. ProxySQL sits between your applications and MySQL, providing connection multiplexing, query routing, query caching, and read/write splitting across your entire infrastructure.

Right-Sizing Your Pool

The optimal pool size is almost always smaller than developers expect. A database server with 16 CPU cores rarely benefits from more than 30-50 active connections. Beyond that, you get diminishing returns from context switching and lock contention.

The formula is straightforward: connections = (core_count * 2) + effective_spindle_count. For SSD-backed systems, start there and adjust based on monitoring data, not guesswork.