calculate maximum total of RU/s in 24 hours for CosmosDB

Question

I set 400 RU/s for my collection in CosmosDB. I want to estimate, maximum total of RU/s in 24 hours. please let me know, how can I calculate it?

is the calculation right? 400 * 60 * 60 * 24 = 34.560.000 RU in 24 hours

Answer 1

When talking about maximum RU available within a given time window, you're correct (except that would be total RU, not total RU/second - it would remain constant at 400/sec unless you adjusted your RU setting).

But... given that RUs are reserved on a per-second basis: What you consume within a given one-second window is really up to you and your specific operations, and if you don't consume all allocated RUs (400, in this case) in a given one-second window, it's gone (you're paying for reserved capacity). So yes, you're right about absolute maximum, but that might not match your real-world scenario. You could end up consuming far less than the maximum you've allocated (imagine idle-times for your app, when you're just not hitting the database much). Also note that RUs are distributed across partitions, so depending on your partitioning scheme, you could end up not using a portion of your available RUs.

Note that it's entirely possible to use more than your allocated 400 RU in a given one-second window, which then puts you into "RU Debt" (see my answer here for a detailed explanation).