DAX Caching

DynamoDB is fast—single-digit millisecond latency is the standard. However, for use cases like high-frequency trading, real-time bidding, or massive multiplayer games, even 5 milliseconds might be too slow.

Enter DynamoDB Accelerator (DAX): a fully managed, in-memory cache that sits transparently between your application and DynamoDB, reducing read latency to microseconds.

1. How DAX Works

DAX is API-compatible with DynamoDB. This means you don’t need to rewrite your application logic to use Redis or Memcached. You simply point your DynamoDB client to the DAX cluster endpoint instead of the standard AWS regional endpoint.

The Write-Through Model

DAX uses a Write-Through caching strategy:

1. Write: Your application writes data to the DAX cluster.
2. Persist: DAX writes the data to the backend DynamoDB table.
3. Ack: Once DynamoDB acknowledges the write, DAX returns success to your application.
4. Cache Update: The item remains in the DAX cache for subsequent reads.

[!NOTE] Write Latency: Because DAX sits in the middle, write operations are slightly slower (extra network hop) than writing directly to DynamoDB. DAX is optimized for read-heavy workloads (e.g., 90% reads, 10% writes).

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2. Interactive: The Latency visualizer

See the difference between standard DynamoDB response times and DAX cached response times.

Standard DynamoDB

DynamoDB + DAX

Ready to test.

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3. Implementation Patterns

Connecting to DAX is almost identical to connecting to standard DynamoDB, with one key difference: the client configuration.

Java SDK v2 Go SDK v2

import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import java.net.URI;

public class DaxConnection {
    public static void main(String[] args) {
        // Standard Client
        DynamoDbClient standardClient = DynamoDbClient.create();

        // DAX Client
        // Note: The Java SDK for DAX is a separate library (amazon-dax-client)
        // that wraps the standard interface.
        // Usually, you create a ClusterDaxClient Config.

        /*
         * Pseudo-code for DAX Client creation as strict v2 support varies:
         *
         * DynamoDbClient daxClient = ClusterDaxClient.builder()
         *     .endpointOverride(URI.create("dax://my-cluster.dax-clusters.us-east-1.amazonaws.com"))
         *     .build();
         */

        System.out.println("Client configured. Operations are identical.");
        // daxClient.getItem(...)
    }
}

package main

import (
	"context"
	"fmt"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
)

func main() {
	// 1. Load Default Config
	cfg, _ := config.LoadDefaultConfig(context.TODO())

	// 2. Configure DAX Endpoint
	// In Go, you typically use a specific DAX client library or
	// configure the EndpointResolver in the standard client if using a proxy.

	/*
	 * Real-world usage often involves the 'aws-dax-go' driver
	 * which implements the DynamoDB API interface.
	 */

	// daxClient, _ := dax.New(cfg, "my-cluster.dax-clusters...")

	// For standard client showing endpoint override concept:
	client := dynamodb.NewFromConfig(cfg, func(o *dynamodb.Options) {
		// This is conceptual; DAX uses a custom protocol (dax://)
		// not supported by standard HTTP client directly without the DAX driver.
		// o.BaseEndpoint = aws.String("dax://my-cluster...")
	})

	fmt.Println("DAX client initialized (requires specific driver)", client)
}

[!IMPORTANT] Production Note: The official AWS SDKs interact with DAX using specific drivers because DAX uses a custom binary protocol, not standard HTTP/JSON, to achieve its speed. You cannot simply change the URL to dax:// in a standard HTTP REST client.

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4. When NOT to use DAX

DAX is powerful, but it’s not a silver bullet. Avoid it if:

1. Strong Consistency Required: DAX is eventually consistent. If you need to read an item immediately after writing it and guarantee you get the new version, you must bypass DAX.
2. Write-Heavy Workloads: If your app is 90% writes, DAX adds overhead without benefit.
3. Cost: DAX clusters are expensive (hourly instance pricing). Ensure your caching hit rate justifies the cost.