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Pagination in DynamoDB: Efficient Data Reading

Introduction

Pagination plays a crucial role in managing and retrieving large datasets from a database. When working with Amazon DynamoDB, a fully managed NoSQL database service, implementing pagination is essential to read data efficiently. In this article, we will explore the concept of pagination in DynamoDB and provide a code example demonstrating how to read data using a partition key.

What is Pagination in DynamoDB?

DynamoDB divides data into partitions for scalability and performance. Each partition contains a portion of the table's data, and the partition key is used to distribute items across these partitions. When retrieving data from DynamoDB, pagination allows you to retrieve a subset of items at a time, reducing the load on the database and improving response times.

Why do we need Pagination in DynamoDB?

Sometimes the use case can be that all of the data that fits the access pattern cannot be in a single partition key; in such scenarios, we will need to use the pagination.

Along with the data size in partitions, there is a limit in the response that aws sdk sends over the network.

Size limits are as follows

  • Query method: 1 MB Response
  • Batch Methods: 16 MB Response

Code Example

Let's examine a code snippet demonstrating how to implement pagination while reading data from DynamoDB using a partition key. The code is written in C# and utilizes the AWS SDK for .NET.

public async Task ReadUsingPartitionKey()
{
    var client = new AmazonDynamoDBClient();
    var request = new QueryRequest()
    {
        TableName = "Products", // YOUR TABLE NAME
        KeyConditionExpression = "partitionkey = :v1", // HERE 'partitionkey' is the column in Products table
        ExpressionAttributeValues = new Dictionary<string, AttributeValue>()
        {
            { ":v1", new AttributeValue() { S = "partition-key-value" } }
        }
    };

    List<Dictionary<string, AttributeValue>> items = new List<Dictionary<string, AttributeValue>>();
    Dictionary<string, AttributeValue> lastEvaluatedKey = null;

    do
    {
        var response = await client.QueryAsync(request);
        items.AddRange(response.Items);
        lastEvaluatedKey = response.LastEvaluatedKey;
        if (lastEvaluatedKey != null && lastEvaluatedKey.Count > 0)
            request.ExclusiveStartKey = lastEvaluatedKey;
        else
            request.ExclusiveStartKey = null;
    } while (lastEvaluatedKey != null && lastEvaluatedKey.Count > 0);

    var response = await client.QueryAsync(request);
    Console.WriteLine(response.Items.Count);
}

Pagination in DynamoDB

Explanation of the Code

  1. The code initializes an instance of the AmazonDynamoDBClient, which provides the necessary methods to interact with DynamoDB.
  2. It creates a QueryRequest object with the appropriate parameters.
    • TableName represents the name of the table from which we want to read data.
    • KeyConditionExpression specifies the condition for the partition key. Adjust this to match your table's partition key column.
    • ExpressionAttributeValues holds the attribute values used in the query. In this example, it sets the partition key value.
  3. The code initializes a list called items to store the retrieved data.
  4. A lastEvaluatedKey dictionary is used to track the position of the last evaluated item during pagination.
  5. The code enters a do-while loop, where it executes the query using the client.QueryAsync(request).
  6. The items retrieved from each iteration are appended to the items list.
  7. The lastEvaluatedKey is updated with the LastEvaluatedKey property of the response, which points to the position of the next page of the results.
  8. If a lastEvaluatedKey exists, it is set as the ExclusiveStartKey in the request object, ensuring the next query starts from the correct position.
  9. The do-while loop continues until there are no more pages to retrieve (i.e., lastEvaluatedKey becomes null or empty).
  10. Finally, the response is printed to the console, indicating the total number of items retrieved.

Conclusion 

Pagination is a crucial technique for efficiently reading data from DynamoDB or any large-scale database. By retrieving data in manageable chunks, you can improve performance, reduce resource consumption, and prevent timeouts. The provided code example demonstrates how to implement pagination using a partition key in DynamoDB, enabling you to retrieve data in a controlled and efficient manner.


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