Connection pooling is a technique used to manage database connections efficiently by creating a cache of connections that can be reused as needed. This approach reduces the overhead of establishing new connections, improves performance, and enhances scalability by reusing existing connections. However, it has limitations in solving all scalability problems and may not inherently scale the database to handle increased load. To address these challenges, YouTube developed Vitess, a connection pooling system that manages connections centrally and eliminates the need for application-level connection pooling. Vitess uses lock-free algorithms and atomic operations to efficiently manage large numbers of concurrent requests. Additionally, MySQL provides settings that can be modified on connections, but this requires careful management to avoid degrading performance. To address this, PlanetScale introduced a "settings pool" feature in Vitess 15, which tracks and manages connections with modified system settings without compromising the benefits of connection pooling.