Sub-second analytics provide game developers with crucial insights into player behavior and engagement. By monitoring these metrics in real time, developers can make data-driven decisions to improve the gaming experience and increase player retention. Key engagement metrics include Time Spent Playing (TSP), Session Length, Session Frequency, Daily Active Users (DAU), Monthly Active Users (MAU), Retention Rate, In-Game Purchases, Average Revenue Per User (ARPU), Average Revenue Per Paying User (ARPPU), Lifetime Value (LTV), and Error Logs. Open-source technologies like ClickHouse can help achieve sub-second analytics with benefits such as flexibility, cost-effectiveness, and community support. Implementing sub-second analytics from the beginning of game development ensures relevant metrics are tracked and data is useful for informed decisions on improving player engagement.