PgHero is an open-source performance dashboard for Postgres (PostgreSQL), a relational database. It is maintained on GitHub by the developer ankane, and its README says it was tested in production at Instacart.
PgHero connects to a database and shows its state in a web page. Query statistics come from pg_stat_statements, a Postgres extension that records how often each query runs and how much time it takes, and the dashboard flags slow queries (by default those that average over 20 ms and run at least 100 times) and long-running queries. With the optional pg_query library it suggests indexes to add. It can store query and space statistics over time in tables, which adds a time-range slider to the Queries tab, and for Amazon RDS and Google Cloud SQL it also shows CPU use and IOPS (disk input and output operations per second). One installation can watch several databases.
PgHero is free and open source under the MIT license. It runs as a Docker image, started with the database address in DATABASE_URL, or as a Rails engine mounted inside a Ruby on Rails application.