DVA-02-Notes/DynamoDB/Practice/Read and Write Units - Set 3.md

DynamoDB Read/Write Units — Numeric Practice, Set 3

20 questions. Give a numeric answer for each, using 1 = <number>, 2 = <number>, and so on.

Assumptions

• Assume provisioned capacity and steady workloads.
• All item sizes are exact DynamoDB item sizes, including attribute names and values.
• Each read accesses an individual item, not a Query or Scan. Transactional operations count individual items, not transaction API calls.
• Normal writes are non-transactional. All writes create new items.
• Ignore indexes, replication, retries, failed requests, burst capacity and partition limits.
• Questions 1–14 ask for exact throughput requirements: fractional RCU answers are valid; do not round the final result to a whole number.
• Questions 15–18 ask for the maximum number of individual item operations per second.
• Questions 19–20 ask for whole-number provisioned capacity settings.

Questions

1. You normally write six separate 1.8 KB items every second. How many WCUs are required?

Answer: ______

2. You normally write nine separate 0.7 KB items every second. How many WCUs are required?

Answer: ______

3. You normally write four separate 3.01 KB items every second. How many WCUs are required?

Answer: ______

4. You transactionally write three separate 2.01 KB items every second. How many WCUs are required?

Answer: ______

5. You transactionally write six separate 1 KB items every second. How many WCUs are required?

Answer: ______

6. You perform strongly consistent reads of five separate 5 KB items every second. How many RCUs of throughput are required?

Answer: ______

7. You perform strongly consistent reads of three separate 12 KB items every second. How many RCUs of throughput are required?

Answer: ______

8. You perform eventually consistent reads of nine separate 0.8 KB items every second. How many RCUs of throughput are required?

Answer: ______

9. You perform eventually consistent reads of five separate 8.01 KB items every second. How many RCUs of throughput are required?

Answer: ______

10. You perform eventually consistent reads of seven separate 8 KB items every second. How many RCUs of throughput are required?

Answer: ______

11. You transactionally read five separate 4.01 KB items every second. How many RCUs of throughput are required?

Answer: ______

12. You transactionally read three separate 11 KB items every second. How many RCUs of throughput are required?

Answer: ______

13. Each second, you normally write two 0.6 KB items and three 2.4 KB items to the same table. How many WCUs are required in total?

Answer: ______

14. Each second, you perform strongly consistent reads of two 5 KB items and eventually consistent reads of three 1 KB items from the same table. How many RCUs of throughput are required in total?

Answer: ______

15. You have 28 WCUs available. What is the maximum number of normal item writes per second you can sustain if each item is 3.2 KB?

Answer: ______

16. You have 30 WCUs available. What is the maximum number of transactional item writes per second you can sustain if each item is 2.2 KB?

Answer: ______

17. You have 15 RCUs available. What is the maximum number of eventually consistent item reads per second you can sustain if each item is 9 KB?

Answer: ______

18. You have 32 RCUs available. What is the maximum number of transactional item reads per second you can sustain if each item is 5 KB?

Answer: ______

19. You perform eventually consistent reads of eleven separate 3 KB items every second. What is the minimum WHOLE NUMBER of RCUs you must provision?

Answer: ______

20. You perform eventually consistent reads of five separate 12.01 KB items every second. What is the minimum WHOLE NUMBER of RCUs you must provision?

Answer: ______

Answer key

Show answers and calculations

ceil means round up to the next whole number. Sizes are divided by the 1 KB write or 4 KB read increment before rounding.

1. 12 WCUs — ceil(1.8 / 1) × 6 = 2 × 6.
2. 9 WCUs — ceil(0.7 / 1) × 9 = 1 × 9.
3. 16 WCUs — ceil(3.01 / 1) × 4 = 4 × 4.
4. 18 WCUs — ceil(2.01 / 1) × 3 × 2 = 3 × 3 × 2.
5. 12 WCUs — ceil(1 / 1) × 6 × 2 = 1 × 6 × 2.
6. 10 RCUs — ceil(5 / 4) × 5 = 2 × 5.
7. 9 RCUs — ceil(12 / 4) × 3 = 3 × 3.
8. 4.5 RCUs — ceil(0.8 / 4) × 9 × 0.5 = 1 × 9 × 0.5.
9. 7.5 RCUs — ceil(8.01 / 4) × 5 × 0.5 = 3 × 5 × 0.5.
10. 7 RCUs — ceil(8 / 4) × 7 × 0.5 = 2 × 7 × 0.5.
11. 20 RCUs — ceil(4.01 / 4) × 5 × 2 = 2 × 5 × 2.
12. 18 RCUs — ceil(11 / 4) × 3 × 2 = 3 × 3 × 2.
13. 11 WCUs — (ceil(0.6 / 1) × 2) + (ceil(2.4 / 1) × 3) = 2 + 9.
14. 5.5 RCUs — (ceil(5 / 4) × 2) + (ceil(1 / 4) × 3 × 0.5) = 4 + 1.5.
15. 7 writes/s — 28 / ceil(3.2 / 1) = 28 / 4.
16. 5 transactional item writes/s — 30 / (ceil(2.2 / 1) × 2) = 30 / 6.
17. 10 reads/s — 15 / (ceil(9 / 4) × 0.5) = 15 / 1.5.
18. 8 transactional item reads/s — 32 / (ceil(5 / 4) × 2) = 32 / 4.
19. 6 provisioned RCUs — ceil(ceil(3 / 4) × 11 × 0.5) = ceil(5.5).
20. 10 provisioned RCUs — ceil(ceil(12.01 / 4) × 5 × 0.5) = ceil(10).

For questions 1–14, RCUs describe exact throughput requirements. Provisioned settings must be whole numbers, as explicitly requested in questions 19–20.