Clickhouse

ClickHouse is an open-source column-oriented database management system (OLAP) designed for real-time analytical queries over large datasets, developed by Yandex (Russia's largest search engine) and open-sourced in 2016. ClickHouse achieves extraordinary query performance by storing data column-by-column (not row-by-row), enabling highly efficient compression and vectorized processing — queries scanning billions of rows return in seconds rather than minutes. ClickHouse processes over 2 petabytes of data daily at Yandex and is used by Cloudflare (handling 10 trillion rows), Uber, eBay, ByteDance, Criteo, and Contentsquare for analytics workloads. The ClickHouse SQL dialect supports complex aggregations, JOINs, window functions, approximate query processing (HyperLogLog, quantile sketches), and time-series operations. MergeTree table engine (ClickHouse's primary storage engine) supports real-time data ingestion via inserts while simultaneously serving queries. ClickHouse Cloud (launched 2022) provides a fully managed service on AWS, GCP, and Azure. Altinity offers enterprise ClickHouse support and Altinity.Cloud. ClickHouse competes with Apache Druid and Apache Pinot for real-time analytics, and with BigQuery/Snowflake/Redshift for analytical queries — typically outperforming managed warehouses on raw query speed for time-series and event analytics. The database is ideal for web analytics, log analysis, user behavior analytics, and financial tick data.