Promscale is an open-source long-term store for Prometheus data designed for analytics, offering a horizontally scalable and operationally mature platform that combines the power of PromQL and SQL. It was built on top of TimescaleDB and PostgreSQL to provide durable, highly-available long-term storage and advanced analytics capabilities. Promscale stores data in a dynamically auto-generated schema optimized for Prometheus metrics and supports features like joins, filters, and statistics. The system can be queried both in PromQL and SQL, enabling users to analyze metrics through easy-to-use SQL views. It also provides features like efficient aggregation by series, logs and traces alongside metrics, and isolation between different metrics. Promscale is designed to address the limitations of Prometheus as a monitoring solution, providing a platform for deep analytics of Prometheus data.