From b0bd0dd71e8921ad5cfacbb7c525750c3a6bb8b83c6d537a9dd1826e3f12bbcb Mon Sep 17 00:00:00 2001 From: Ember Date: Mon, 2 Nov 2026 14:09:37 +0000 Subject: [PATCH 1/2] Add 20 numeric DynamoDB capacity practice questions --- .../Practice/Read and Write Units - Set 3.md | 96 +++++++++++++++++++ 1 file changed, 96 insertions(+) create mode 100644 DynamoDB/Practice/Read and Write Units - Set 3.md diff --git a/DynamoDB/Practice/Read and Write Units - Set 3.md b/DynamoDB/Practice/Read and Write Units - Set 3.md new file mode 100644 index 0000000..44a7739 --- /dev/null +++ b/DynamoDB/Practice/Read and Write Units - Set 3.md @@ -0,0 +1,96 @@ +# DynamoDB Read/Write Units — Numeric Practice, Set 3 + +20 questions. Give a numeric answer for each, using `1 = `, `2 = `, 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: ______ From 3a745faea59b8d83d921c51a0df2dbd2c8cefb55768a81e52296b4e48de17171 Mon Sep 17 00:00:00 2001 From: Ember Date: Mon, 2 Nov 2026 14:17:07 +0000 Subject: [PATCH 2/2] Add checked answer key and calculations for all 20 questions --- .../Practice/Read and Write Units - Set 3.md | 32 +++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/DynamoDB/Practice/Read and Write Units - Set 3.md b/DynamoDB/Practice/Read and Write Units - Set 3.md index 44a7739..57d423a 100644 --- a/DynamoDB/Practice/Read and Write Units - Set 3.md +++ b/DynamoDB/Practice/Read and Write Units - Set 3.md @@ -94,3 +94,35 @@ 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. + +