Request Units (RUs) measure the compute and I/O resources consumed when a user or application queries a database. Different queries will “cost” different amounts of Request Units; a small read request might cost just a few RUs, whereas a full table scan could cost many.
Similarly, a database serving an application with millions of users (and thus millions of read/write requests) will consume RUs at a much faster pace than a database that’s rarely used.
RUs provide a convenient way to track resource consumption and billing for serverless databases, although different databases may define and price RUs in different ways. In the case of CockroachDB Serverless specifically, all users are allocated 250 million RUs of usage per month for free, with a cost of $1 per additional 10 million RUs after that.