Consistent vs eventually consistent reads in DynamoDB - Hands-On Comparison

Consistent vs Eventually Consistent Reads in DynamoDB

📖 Scenario: You are building a simple inventory system for a small online store using DynamoDB. You want to understand how to read data with different consistency models to ensure your application behaves correctly.

🎯 Goal: Learn how to perform consistent and eventually consistent reads on a DynamoDB table by writing queries with the correct parameters.

📋 What You'll Learn

Create a DynamoDB table data structure with sample items

Add a configuration variable to select read consistency

Write a query to read an item using the selected consistency

Complete the query with the correct parameter to enforce consistency

💡 Why This Matters

🌍 Real World

Understanding consistent and eventually consistent reads helps developers build applications that balance performance and data accuracy when using DynamoDB.

💼 Career

Many cloud and backend developer roles require knowledge of NoSQL databases like DynamoDB and how to manage data consistency for scalable applications.

1

Create DynamoDB table data with sample items

Create a variable called inventory that represents a DynamoDB table with these exact items: {'ProductID': 'P100', 'Name': 'T-shirt', 'Stock': 50} and {'ProductID': 'P101', 'Name': 'Jeans', 'Stock': 30}.

DynamoDB

# Create the inventory table data with two items
# Your code here

Need a hint?

Use a list of dictionaries to represent the table items exactly as shown.

2

Add a configuration variable for read consistency

Create a variable called consistent_read and set it to True to indicate you want a strongly consistent read.

DynamoDB

inventory = [
    {'ProductID': 'P100', 'Name': 'T-shirt', 'Stock': 50},
    {'ProductID': 'P101', 'Name': 'Jeans', 'Stock': 30}
]
# Set consistent_read to True for strong consistency
# Your code here

Need a hint?

Set consistent_read exactly to True.

3

Write a query to read an item using the consistency setting

Write a function called get_item that takes product_id and returns the item from inventory with matching 'ProductID'. Use the variable consistent_read to simulate the read consistency (no actual delay needed).

DynamoDB

inventory = [
    {'ProductID': 'P100', 'Name': 'T-shirt', 'Stock': 50},
    {'ProductID': 'P101', 'Name': 'Jeans', 'Stock': 30}
]
consistent_read = True

# Define get_item function to find item by ProductID
# Your code here

Need a hint?

Use a for loop to find the item with matching ProductID.

4

Complete the query with the consistency parameter

Add a variable called read_params as a dictionary with the key 'ConsistentRead' set to the value of consistent_read. This simulates passing the consistency option to DynamoDB's get_item method.

DynamoDB

inventory = [
    {'ProductID': 'P100', 'Name': 'T-shirt', 'Stock': 50},
    {'ProductID': 'P101', 'Name': 'Jeans', 'Stock': 30}
]
consistent_read = True

def get_item(product_id):
    for item in inventory:
        if item['ProductID'] == product_id:
            return item
    return None

# Add read_params dictionary with 'ConsistentRead' key
# Your code here

Need a hint?

Create read_params dictionary with the key exactly as 'ConsistentRead' and value consistent_read.