azure - How is cosmosDB RU throughput enforced

Question

I have a cosmosGB gremlin API set up with 400 RU/s. If I have to run a query that needs 800 RUs, does it mean that this query takes 2 sec to execute? If i increase the throughput to 1600 RU/s, does this query execute in half a second? I am not seeing any significant changes in query performance by playing around with the RUs.

Answer 1

As I explained in a different, but somewhat related answer here, Request Units are allocated on a per-second basis. In the event a given query will cost more than the number of Request Units available in that one-second window:

• The query will be executed
• You will now be in "debt" by the overage in Request Units
• You will be throttled until your "debt" is paid off

Let's say you had 400 RU/sec, and you executed a query that cost 800 RU. It would complete, but then you'd be in debt for around 2 seconds (400 RU per second, times two seconds). At this point, you wouldn't be throttled anymore.

The speed in which a query executes does not depend on the number of RU allocated. Whether you had 1,000 RU/second OR 100,000 RU/second, a query would run in the same amount of time (aside from any throttle time preventing the query from running initially). So, aside from throttling, your 800 RU query would run consistently, regardless of RU count.