ClickHouse

ClickHouse is an open-source column-oriented database management system that allows generating analytical data reports in real-time. Analytical queries sweep billions of rows, and a row-oriented database has to read every column to answer them. That is the cost ClickHouse was built to remove.

Tables are stored as a collection of columns, with the values of each column stored sequentially one after the other, so a query touches only the columns it names. The documentation reports a sample query processing 100 million rows in 92 milliseconds, over a billion rows per second or just under 7 GB per second.

Several engineering decisions follow from that layout.

• SQL query language: a declarative language with GROUP BY, ORDER BY, subqueries, JOINs and window functions.
• Multi-master replication: an asynchronous scheme storing data redundantly on multiple nodes.
• Adaptive joins: the engine chooses between hash and merge algorithms per query.
• Accuracy traded for speed: approximate aggregations and sampling when an exact answer is not worth the wait.
• Role based access control: permissions modeled on the ANSI SQL standard.

Installing on Linux, macOS or FreeBSD is a single shell command from the project's site. The same engine runs as self-managed open source under Apache 2.0 or as ClickHouse Cloud, a managed service built by the creators and maintainers. Releases land monthly, each introduced by a public community call whose recording and slides stay online.