[RyanHamilton]

For real-time and large historical data, open source there's tdengine/questdb, commercial DolphinDB and kdb+. If you only need fast recent data and not large historical embedding is a good solution which means h2/duckdb/sqlite if open source, extremedb if commercial. I've benchmarked and ran applications on most these databases including running real-time analytics.

[qoega]

Open-source ClickHouse also allows both real-time and large historical data.

[nhourcard]

QuestDB, kdb+ and others mentioned are more geared toward time-series workloads, while Clickhouse is more toward OLAP. There are also exciting solutions on the streaming side of things with RisingWave etc.