What is Columnar?

Columnar storage is a data storage technique where data is stored in columns rather than rows. This is particularly efficient for analytical queries that only need to access a subset of columns, as it reduces I/O and allows for better compression. Columnar databases are commonly used in data warehousing, business intelligence, and big data analytics where large datasets are queried to extract insights. Examples include Apache Cassandra, Apache Parquet, and ClickHouse.