How would a "hot" hash key affect throughout in practice on Amazon DynamoDB?

Question

First, here's a support document for DyanamoDB giving guidance on how to avoid a "hot" hash key.

Conceptually, a hot hash key is simple and they are (typically) straightforward to avoid - the documents give good examples of how to do so. I am not asking what a hot hash key is.

What I do want to know is how much would throughout performance actually degrade for a given level of provisioned read/write units at the limit, that is, when all read/write activity is focused on only one (or very few) partition(s). For properly distributed hash key activity (uniform across partitions), DynamoDB gives single millisecond response times. So, what would response times look like in the worst case scenario?

Here's a post on AWS asking a related question which gives a specific use-case where knowledge of this answer matters.

Answer 1

DynamoDB will also guarantee you single millisecond response times, even for your 'hot' hash key, BUT you will very likely see a lot throttled requests. And that even when you seem to have plenty of unspent provisioned throuput. That is because your provisioned throuput gets effectively divided by the number of partitions. But as you don't know how many partitions there are at a given time, it varies how much of your provisioned throuput you can spent for a single hashkey...