A database is an organized collection of data.

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One of the first steps in creating any database table is deciding what kind of data will uniquely identify a given row in said table; we call this a primary key.

A lot of the complexities involved in actually building a database engine aren’t related to the core features that you want to have. They are related to what looks like peripheral concerns. Backup / restore is an excellent example of that.

Cassandra isn’t a relational database management system, but it has some features that make it look a bit like one.