Read and write capacity units in DynamoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the read capacity units to 5 in the DynamoDB table creation.

DynamoDB

TableName: "MyTable",
ProvisionedThroughput: {
  ReadCapacityUnits: [1],
  WriteCapacityUnits: 10
}

Drag options to blanks, or click blank then click option'

A5

B20

C0

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing read capacity units with write capacity units.

Setting the value to zero which disables reads.

The read capacity units specify how many strongly consistent reads per second the table can handle. Setting it to 5 means the table can handle 5 such reads per second.

2fill in blank

medium

Complete the code to set the write capacity units to 15 in the DynamoDB table creation.

DynamoDB

TableName: "Orders",
ProvisionedThroughput: {
  ReadCapacityUnits: 10,
  WriteCapacityUnits: [1]
}

Drag options to blanks, or click blank then click option'

A10

B5

C15

D20

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up read and write capacity units.

Choosing a value less than the required 15.

Write capacity units define how many writes per second the table can handle. Setting it to 15 means the table can handle 15 writes per second.

3fill in blank

hard

Fix the error in the code by choosing the correct value for read capacity units (must be a positive integer).

DynamoDB

ProvisionedThroughput: {
  ReadCapacityUnits: [1],
  WriteCapacityUnits: 10
}

Drag options to blanks, or click blank then click option'

A-5

B10

C0

D"five"

Attempts:

3 left

💡 Hint

Common Mistakes

Using zero or negative numbers.

Using strings instead of numbers.

Read capacity units must be a positive integer. 10 is valid, while negative numbers, zero, or strings are invalid.

4fill in blank

hard

Fill both blanks to set read capacity units to 8 and write capacity units to 12.

DynamoDB

ProvisionedThroughput: {
  ReadCapacityUnits: [1],
  WriteCapacityUnits: [2]
}

Drag options to blanks, or click blank then click option'

A8

B12

C5

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping read and write capacity values.

Using incorrect numbers.

Read capacity units are set to 8 and write capacity units to 12 as required.

5fill in blank

hard

Fill all three blanks to create a DynamoDB table with name 'Users', read capacity units 6, and write capacity units 9.

DynamoDB

CreateTable({
  TableName: [1],
  ProvisionedThroughput: {
    ReadCapacityUnits: [2],
    WriteCapacityUnits: [3]
  }
})

Drag options to blanks, or click blank then click option'

A"Users"

B6

C9

D"Orders"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong table name.

Mixing up read and write capacity units.

Omitting quotes around the table name.

The table name is 'Users', read capacity units are 6, and write capacity units are 9 as specified.

Practice

1. What do read and write capacity units control in a DynamoDB table?

easy

A. The number of reads and writes the table can handle per second

B. The size of the data stored in the table

C. The number of tables in the database

D. The security settings of the table

Solution

1. Step 1: Understand capacity units meaning

   Read and write capacity units define how many read and write operations a DynamoDB table can perform each second.

2. Step 2: Identify what capacity units control

   They control throughput, not storage size, number of tables, or security settings.

3. Final Answer:

   The number of reads and writes the table can handle per second -> Option A

4. Quick Check:

   Capacity units = throughput control [OK]

Hint: Capacity units = max reads/writes per second [OK]

Common Mistakes:

• Confusing capacity units with storage size
• Thinking capacity units control security
• Assuming capacity units limit number of tables

2. Which of the following is the correct way to specify write capacity units when creating a DynamoDB table using AWS CLI?

easy

A. --capacity ReadUnits=5,WriteUnits=10

B. --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=10

C. --throughput ReadCapacity=5 WriteCapacity=10

D. --provisioned-throughput ReadUnits=5 WriteUnits=10

Solution

1. Step 1: Recall AWS CLI syntax for capacity units

   The correct syntax uses --provisioned-throughput with ReadCapacityUnits and WriteCapacityUnits keys.

2. Step 2: Match options with correct syntax

   --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=10 matches the exact syntax; others use incorrect keys or formats.

3. Final Answer:

   --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=10 -> Option B

4. Quick Check:

   Correct CLI syntax = --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=10 [OK]

Hint: Look for 'ReadCapacityUnits' and 'WriteCapacityUnits' keys [OK]

Common Mistakes:

• Using incorrect keys like ReadUnits or WriteUnits
• Missing commas or using wrong separators
• Confusing throughput with capacity keywords

3. A DynamoDB table has 10 write capacity units. If each write item is 2 KB, how many writes per second can the table handle without throttling?

medium

A. 5 writes per second

B. 10 writes per second

C. 20 writes per second

D. 1 write per second

Solution

1. Step 1: Understand write capacity unit size

   One write capacity unit allows one write per second for an item up to 1 KB.

2. Step 2: Calculate writes for 2 KB items

   Each 2 KB item requires 2 write capacity units. With 10 units, 10 / 2 = 5 writes per second.

3. Final Answer:

   5 writes per second -> Option A

4. Quick Check:

   Write capacity units / item size factor = writes/sec [OK]

Hint: Divide capacity units by item size in KB [OK]

Common Mistakes:

• Assuming 1 unit = 2 KB write
• Not dividing capacity units by item size
• Confusing read and write capacity units

4. You set a DynamoDB table's read capacity units to 5 but your application experiences throttling at 3 reads per second. What is the most likely cause?

medium

A. The table is in the wrong AWS region

B. The table has too many write capacity units

C. Each read item is larger than 4 KB, requiring more capacity units

D. The table's storage size is too large

Solution

1. Step 1: Recall read capacity unit size

   One read capacity unit supports one strongly consistent read per second for an item up to 4 KB.

2. Step 2: Analyze throttling cause

   If items are larger than 4 KB, each read consumes multiple units, so 5 units may not support 3 reads per second.

3. Final Answer:

   Each read item is larger than 4 KB, requiring more capacity units -> Option C

4. Quick Check:

   Item size affects read capacity usage [OK]

Hint: Check item size vs 4 KB read unit size [OK]

Common Mistakes:

• Blaming write capacity units for read throttling
• Ignoring item size impact on capacity
• Thinking region or storage size causes throttling

5. You want to optimize costs for a DynamoDB table with variable traffic. Which approach best uses read and write capacity units efficiently?

hard

A. Set capacity units to zero when not using the table

B. Set very high fixed capacity units to avoid throttling

C. Manually increase capacity units once a month

D. Use on-demand capacity mode to automatically adjust units based on traffic

Solution

1. Step 1: Understand capacity modes

   DynamoDB offers on-demand mode that adjusts capacity automatically to traffic, optimizing cost and performance.

2. Step 2: Compare options for cost efficiency

   Setting high fixed units wastes money; manual changes are slow; zero units disables table. On-demand is best for variable traffic.

3. Final Answer:

   Use on-demand capacity mode to automatically adjust units based on traffic -> Option D

4. Quick Check:

   On-demand mode = auto scaling capacity [OK]

Hint: Choose on-demand for variable traffic [OK]

Common Mistakes:

• Setting fixed high capacity wastes money
• Manually adjusting capacity is inefficient
• Setting zero units disables table access