The discussion around calculating number of partitions looks wrong. While it is true that partitions can take up to 10GB of data – under the hood, when it reaches a certain fill level (75% from recollection), it will start splitting into two new partitions. This takes time so in the mean time any new data will still be written to the old partition and the new partitions until such point the new partitions are ready – that’s why 10GB is important. In the quiz, it said the number of partitions when you have 25GB is at least 3. Actually it is at least 4 – you may have 2 partitions of 7GB each and 2 of 5.5GB each, but you cannot have 3 partitions of 8.33GB each. If data is coming in with a random or evenly spread hash key, you would find that you have 6 partitions, each with roughly 4.16 GB of data
I understand that real-world splitting behavior is a little different than the 10 GB / 1000 WCU / 3000 RCU limits. However, these are the limits that are specifically used in the AWS DynamoDB documentation and that’s what we want to teach towards as those are the values that will be used on the exam.
Sometimes, the documentation and exam answers differ from real-world experience and that’s just a trade-off we have to make on a Certification course. Otherwise, we’d be caveating everything and confusing students immensely.