tl;dr: PgDog, an open-source proxy that horizontally scales Postgres via sharding, has raised $5.5M from Basis Set, YC, and Pioneer Fund. Built by ex-Instacart engineers who scaled Postgres there, it currently handles 2M+ queries per second across production deployments and has sharded 20TB+. It ships as a Docker image deployable anywhere, with a paid Enterprise edition for AWS planned.