Note: This term is specific to CockroachDB, a Distributed SQL database. In other contexts, it may be used differently.
The key value layer is a figurative layer of CockroachDB. One helpful way to think about the architecture of CockroachDB is as a SQL system built on top of a key value store. When the data is up in the top layers, it follows the rules of a SQL system and is structured in a table format. When the data travels deeper into the database, table format no longer works, due to the distributed nature of the database. So instead of being stored in tables, the data is stored in a different way: in key-value pairs. It’s important to note that this combination of a SQL upper layer with a key-value store underneath is a relatively unusual setup, because translating structured table data into key-value pairs is a difficult task.
Note: This term is specific to CockroachDB, a Distributed SQL database. In other contexts, it may be used differently.
A key-value pair is a way of storing data. In CockroachDB, individual rows from the tables are mapped into key-value pairs. One column becomes the index, meaning that each piece of data in that column is the “key” in its own key-value pair. One or more other columns become the “value.”
For example, in a table called “Customer Data” the first column might be “Name,” the second “Hometown” and the third “Email Address.” You might decide that the “Name” should be the key because ultimately you want all your data to be sorted by name. Then you might decide that the “Hometown” and “Email Address” columns should be the values.
This information gets mapped, row-by-row, into key-value pairs, and the ultimate format of a single row might end up reading as a string: “Customer Data Table/John Smith/New York City/Johnsmith@gmail.com.” Then, once all the data in the table is translated into the monolithic sorted key-value map, these pieces of data are all sorted by the name value.