Creating a DynamoDB table in AWS - Performance & Efficiency

Time Complexity: Creating a DynamoDB table

O(n)

Understanding Time Complexity

When creating a DynamoDB table, it is important to understand how the time to complete the creation grows as we add more tables.

We want to know how the number of tables affects the time it takes to create a new one.

Scenario Under Consideration

Analyze the time complexity of the following operation sequence.

# Create a DynamoDB table
aws dynamodb create-table \
  --table-name MyTable \
  --attribute-definitions AttributeName=Id,AttributeType=S \
  --key-schema AttributeName=Id,KeyType=HASH \
  --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5
    

This operation creates a single DynamoDB table with a primary key and provisioned throughput settings.

Identify Repeating Operations

Identify the API calls, resource provisioning, data transfers that repeat.

• Primary operation: The API call to create a DynamoDB table.
• How many times: Once per table creation request.

How Execution Grows With Input

Each time you create a new table, you make one API call that provisions that table.

Input Size (n)	Approx. Api Calls/Operations
10	10
100	100
1000	1000

Pattern observation: The number of API calls grows directly with the number of tables created.

Final Time Complexity

Time Complexity: O(n)

This means the time to create tables grows linearly with how many tables you want to create.

Common Mistake

[X] Wrong: "Creating multiple tables happens all at once and takes the same time as creating one."

[OK] Correct: Each table creation is a separate operation that takes time, so more tables mean more total time.

Interview Connect

Understanding how resource creation scales helps you design systems that handle growth smoothly and predict delays when provisioning resources.

Self-Check

"What if we changed to creating tables in parallel instead of one after another? How would the time complexity change?"

Practice

1. What is the main purpose of the primary key when creating a DynamoDB table?

easy

A. To define the table's read capacity

B. To store the table's name

C. To specify the AWS region

D. To uniquely identify each item in the table

Solution

1. Step 1: Understand the role of the primary key

   The primary key uniquely identifies each item in a DynamoDB table, ensuring no duplicates.

2. Step 2: Differentiate from other table properties

   Table name, capacity, and region do not serve as unique identifiers for items.

3. Final Answer:

   To uniquely identify each item in the table -> Option D

4. Quick Check:

   Primary key = unique item ID [OK]

Hint: Primary key means unique ID for each item [OK]

Common Mistakes:

• Confusing primary key with table name
• Thinking capacity defines uniqueness
• Mixing region with key attributes

2. Which AWS CLI command correctly creates a DynamoDB table named Users with a primary key UserId of type string?

easy

A. aws dynamodb create-table --table-name Users --attribute-definitions AttributeName=UserId,AttributeType=S --key-schema AttributeName=UserId,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

B. aws dynamodb create-table --name Users --key UserId --type String

C. aws dynamodb make-table --table Users --key UserId --type S

D. aws dynamodb create-table --table Users --attribute UserId String --key UserId HASH

Solution

1. Step 1: Identify correct AWS CLI syntax for creating a table

   The correct command uses create-table with --table-name, --attribute-definitions, --key-schema, and --provisioned-throughput.

2. Step 2: Verify attribute and key schema details

   AttributeName=UserId with AttributeType=S (string) and KeyType=HASH for primary key is correct.

3. Final Answer:

   aws dynamodb create-table --table-name Users --attribute-definitions AttributeName=UserId,AttributeType=S --key-schema AttributeName=UserId,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5 -> Option A

4. Quick Check:

   Correct CLI syntax = aws dynamodb create-table --table-name Users --attribute-definitions AttributeName=UserId,AttributeType=S --key-schema AttributeName=UserId,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5 [OK]

Hint: Use --attribute-definitions and --key-schema for keys [OK]

Common Mistakes:

• Using wrong command like make-table
• Missing provisioned throughput
• Incorrect flags like --name instead of --table-name

3. Given this AWS CLI command:

aws dynamodb create-table --table-name Products --attribute-definitions AttributeName=ProductId,AttributeType=S AttributeName=Category,AttributeType=S --key-schema AttributeName=ProductId,KeyType=HASH AttributeName=Category,KeyType=RANGE --provisioned-throughput ReadCapacityUnits=10,WriteCapacityUnits=5

What is the primary key type of the Products table?

medium

A. No primary key defined

B. Simple primary key with only a HASH key

C. Composite primary key with HASH and RANGE keys

D. Primary key with only a RANGE key

Solution

1. Step 1: Analyze the key schema in the command

   The command defines two keys: ProductId as HASH and Category as RANGE.

2. Step 2: Understand primary key types in DynamoDB

   A primary key with both HASH and RANGE keys is called a composite primary key.

3. Final Answer:

   Composite primary key with HASH and RANGE keys -> Option C

4. Quick Check:

   HASH + RANGE = composite key [OK]

Hint: HASH + RANGE keys mean composite primary key [OK]

Common Mistakes:

• Thinking two attributes mean no key
• Confusing RANGE key as standalone primary key
• Ignoring key-schema details

4. You run this command to create a DynamoDB table:

aws dynamodb create-table --table-name Orders --attribute-definitions AttributeName=Id,AttributeType=N --key-schema AttributeName=OrderId,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

But you get an error. What is the most likely cause?

medium

A. The attribute definition and key schema attribute names do not match

B. Provisioned throughput values are missing

C. The key schema is missing a RANGE key

D. AttributeType should be 'S' for string, not 'N' for number

Solution

1. Step 1: Check attribute definitions and key schema names

   The attribute definitions specify AttributeName=Id, but the key schema specifies AttributeName=OrderId. The names do not match, causing the error.

2. Step 2: Verify other potential issues

   Provisioned throughput values are present (not B), a simple primary key with only HASH is allowed (not C), AttributeType=N is valid for numeric IDs (not D).

3. Final Answer:

   The attribute definition and key schema attribute names do not match -> Option A

4. Quick Check:

   Attribute names must match exactly [OK]

Hint: Match attribute names exactly in definitions and key schema [OK]

Common Mistakes:

• Assuming 'N' type is invalid
• Expecting RANGE key for all tables
• Missing provisioned throughput

5. You want to create a DynamoDB table named Sessions with a composite primary key: UserId (string) as HASH and SessionId (string) as RANGE. You also want to set autoscaling for read and write capacity. Which of the following is the best approach?

hard

A. Create the table without specifying key schema and add keys later

B. Use aws dynamodb create-table with attribute definitions and key schema, then configure autoscaling via Application Auto Scaling service

C. Use aws dynamodb create-table with only HASH key and enable autoscaling in the same command

D. Create the table with fixed provisioned throughput and manually update capacity when needed

Solution

1. Step 1: Define table with composite primary key

   Use create-table with attribute definitions for UserId and SessionId, and key schema with HASH and RANGE keys.

2. Step 2: Configure autoscaling separately

   DynamoDB autoscaling is set up via Application Auto Scaling service after table creation; it cannot be enabled directly in create-table command.

3. Final Answer:

   Use aws dynamodb create-table with attribute definitions and key schema, then configure autoscaling via Application Auto Scaling service -> Option B

4. Quick Check:

   Composite key + separate autoscaling setup = Use aws dynamodb create-table with attribute definitions and key schema, then configure autoscaling via Application Auto Scaling service [OK]

Hint: Create table first, then set autoscaling separately [OK]

Common Mistakes:

• Trying to enable autoscaling in create-table command
• Skipping RANGE key for composite key
• Creating table without key schema