Valueless Column in Cassandra

Column keys can store values as shown in the Modeling by query section. There is no "Not Null" concept in Cassandra such that column values can store empty values without any problem. Simply storing data in column keys while leaving empty values in the column, known as a valueless column, is sometimes used purposely.


Motivation:

One motivation for valueless columns is the sort-by-column-key feature of Cassandra. Nonetheless, there are some limitations and caveats. The maximum size of a column key is 64 KB, in contrast to 2 GB for a column value. Therefore, space in a column key is limited. Furthermore, using timestamp alone as a column key can result in timestamp collision.

Application:

Cassandra is a perfect fit for storing time-series data. Because one row can hold as many as 2 billion variable columns. It is a single layout on disk, based on the storage model. Therefore, Cassandra can handle voluminous time-series data in a blazing fast fashion. TTL is another excellent feature to simplify data housekeeping.