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Note: There is some term confusion in the industry, and two different things are called "Columnar Databases". Some, listed here, are distributed, persistent databases built around the "key-map" data model: all data has a (possibly composite) key, with which a map of key-value pairs is associated. In some systems, multiple such value maps can be associated with a key, and these maps are referred to as "column families" (with value map keys being referred to as "columns").
Another group of technologies that can also be called "columnar databases" is distinguished by how it stores data, on disk or in memory -- rather than storing data the traditional way, where all column values for a given key are stored next to each other, "row by row", these systems store all column values next to each other. So more work is needed to get all columns for a given key, but less work is needed to get all values for a given column.
The former group is referred to as "key map data model" here. The line between these and the Key-value Data Model stores is fairly blurry.
The latter, being more about the storage format than about the data model, is listed under Columnar Databases.
You can read more about this distinction on Prof. Daniel Abadi's blog: Distinguishing two major types of Column Stores.
Note please read the note on Key-Map Data Model section.