Understanding Request Units in Azure Cosmos DB

One of the most interesting database solutions on Microsoft's Azure cloud platform is the Cosmos DB database. Microsoft itself describes the service as a "globally distributed multi-model database". One important "currency" (as Microsoft puts it) is the Request Unit, or RU.

Shortly put, a request unit is the measurement performance and billing unit and is not a simple counter on database reads or writes, for example. Instead, request units provide a combination of data storage, CPU and memory usage. They are also reserved for a database, and thus you will always get predictable performance out of it.

For more details, see the Azure documentation. It even points you to a request unit calculator, which allows you to predict how many RUs you need.