# DAX SDK for Go
<a name="DAX.client.run-application-go-2"></a>

按照此过程操作，在 Amazon EC2 实例上运行 Amazon DynamoDB Accelerator (DAX) SDK for Go 示例应用程序。

**为 DAX 运行 SDK for Go 示例**

1. 在 Amazon EC2 实例设置 SDK for Go：

   1. 安装 Go 编程语言 (`Golang`)。

      ```
      sudo yum install -y golang
      ```

   1. 测试 Golang 是否已安装且运行正常。

      ```
      go version
      ```

      应该显示类似下面的消息。

      ```
      go version go1.23.4 linux/amd64
      ```

1. 安装 Golang 示例应用程序。

   ```
   go get github.com/aws-samples/sample-aws-dax-go-v2
   ```

1. 运行以下 Golang 程序。第一个程序创建一个名为 `TryDaxGoTable` 的 DynamoDB 表。第二个程序向表中写入数据。

   ```
   go run ~/go/pkg/mod/github.com/aws-samples/sample-aws-dax-go-v2@v1.0.0/try_dax.go -service dynamodb -command create-table
   ```

   ```
   go run ~/go/pkg/mod/github.com/aws-samples/sample-aws-dax-go-v2@v1.0.0/try_dax.go -service dynamodb -command put-item
   ```

1. 运行以下 Golang 程序。

   ```
   go run ~/go/pkg/mod/github.com/aws-samples/sample-aws-dax-go-v2@v1.0.0/try_dax.go -service dynamodb -command get-item
   ```

   ```
   go run ~/go/pkg/mod/github.com/aws-samples/sample-aws-dax-go-v2@v1.0.0/try_dax.go -service dynamodb -command query
   ```

   ```
   go run ~/go/pkg/mod/github.com/aws-samples/sample-aws-dax-go-v2@v1.0.0/try_dax.go -service dynamodb -command scan
   ```

   记下计时信息—`GetItem`、`Query` 和 `Scan` 测试所需的时间（以毫秒为单位）。

1. 在上一步中，您已针对 DynamoDB 端点运行程序。现在，重新运行这些程序，但此次，`GetItem`、`Query` 和 `Scan` 操作将由 DAX 集群处理。

   要确定 DAX 集群的端点，请选择下列选项之一：
   + **使用 DynamoDB 控制台** — 选择 DAX 集群。集群端点显示在控制台中，如下面的示例所示。

     ```
     dax://my-cluster.l6fzcv.dax-clusters.us-east-1.amazonaws.com
     ```
   + **使用 AWS CLI** — 输入下面的命令。

     ```
     aws dax describe-clusters --query "Clusters[*].ClusterDiscoveryEndpoint"
     ```

     集群端点显示在输出中，如下面的示例所示。

     ```
     {
         "Address": "my-cluster.l6fzcv.dax-clusters.us-east-1.amazonaws.com",
         "Port": 8111,
         "URL": "dax://my-cluster.l6fzcv.dax-clusters.us-east-1.amazonaws.com"
     }
     ```

   现在再次运行这些程序，但这次将集群端点指定为命令行参数。

   ```
   go run ~/go/pkg/mod/github.com/aws-samples/sample-aws-dax-go-v2@v1.0.0/try_dax.go -service dax -command get-item -endpoint my-cluster.l6fzcv.dax-clusters.us-east-1.amazonaws.com:8111
   ```

   ```
   go run ~/go/pkg/mod/github.com/aws-samples/sample-aws-dax-go-v2@v1.0.0/try_dax.go -service dax -command query -endpoint my-cluster.l6fzcv.dax-clusters.us-east-1.amazonaws.com:8111
   ```

   ```
   go run ~/go/pkg/mod/github.com/aws-samples/sample-aws-dax-go-v2@v1.0.0/try_dax.go -service dax -command scan -endpoint my-cluster.l6fzcv.dax-clusters.us-east-1.amazonaws.com:8111
   ```

   ```
   go run ~/go/pkg/mod/github.com/aws-samples/sample-aws-dax-go-v2@v1.0.0/try_dax.go -service dax -command paginated-scan -endpoint my-cluster.l6fzcv.dax-clusters.us-east-1.amazonaws.com:8111
   ```

   ```
   go run ~/go/pkg/mod/github.com/aws-samples/sample-aws-dax-go-v2@v1.0.0/try_dax.go -service dax -command paginated-query -endpoint my-cluster.l6fzcv.dax-clusters.us-east-1.amazonaws.com:8111
   ```

   ```
   go run ~/go/pkg/mod/github.com/aws-samples/sample-aws-dax-go-v2@v1.0.0/try_dax.go -service dax -command paginated-batch-get -endpoint my-cluster.l6fzcv.dax-clusters.us-east-1.amazonaws.com:8111
   ```

   查看输出的其余内容，并记下计时信息。与 DynamoDB 相比，使用 DAX 时，`GetItem`、`Query` 和 `Scan` 的运行时间应明显更短。

1. 运行以下 Golang 程序以删除 `TryDaxGoTable`。

   ```
   go run ~/go/pkg/mod/github.com/aws-samples/sample-aws-dax-go-v2@v1.0.0/try_dax.go -service dynamodb -command delete-table
   ```

## 与 适用于 Go 的 AWS SDK V2 不对等的功能
<a name="DAX.client.run-application-go-features-not-in-parity"></a>

中间件堆栈：DAX Go V2 不支持通过 API 选项使用中间件堆栈。有关更多信息，请参阅 [Customizing the 适用于 Go 的 AWS SDK v2 Client Requests with Middleware](https://docs.aws.amazon.com/sdk-for-go/v2/developer-guide/middleware.html#:~:text=You%20can%20customize%20AWS%20SDK,step's%20input%20and%20output%20types)。

示例：

```
// Custom middleware implementation
type customSerializeMiddleware struct{}
// ID returns the identifier for the middleware
func (m *customSerializeMiddleware) ID() string {
    return "CustomMiddleware"
}
// HandleSerialize implements the serialize middleware handler
func (m *customSerializeMiddleware) HandleSerialize(
    ctx context.Context,
    in middleware.SerializeInput,
    next middleware.SerializeHandler,
) (
    out middleware.SerializeOutput,
    metadata middleware.Metadata,
    err error,
) {
    // Add your custom logic here before the request is serialized
    fmt.Printf("Executing custom middleware for request: %v\n", in)
    // Call the next handler in the middleware chain
    return next.HandleSerialize(ctx, in)
}

func executeGetItem(ctx context.Context) error {
    client, err := initItemClient(ctx)
    if err != nil {
        os.Stderr.WriteString(fmt.Sprintf("failed to initialize client: %v\n", err))
        return err
    }

    st := time.Now()
    for c := 0; c < iterations; c++ {
        for i := 0; i < pkMax; i++ {
            for j := 0; j < skMax; j++ {
                // Create key using attributevalue.Marshal for type safety
                pk, err := attributevalue.Marshal(fmt.Sprintf("%s_%d", keyPrefix, i))
                if err != nil {
                    return fmt.Errorf("error marshaling pk: %v", err)
                }
                sk, err := attributevalue.Marshal(fmt.Sprintf("%d", j))
                if err != nil {
                    return fmt.Errorf("error marshaling sk: %v", err)
                }
                key := map[string]types.AttributeValue{
                    "pk": pk,
                    "sk": sk,
                }
                in := &dynamodb.GetItemInput{
                    TableName: aws.String(table),
                    Key:       key,
                }

                // Custom middleware option
                customMiddleware := func(o *dynamodb.Options) {
                    o.APIOptions = append(o.APIOptions, func(stack *middleware.Stack) error {
                        // Add custom middleware to the stack
                        return stack.Serialize.Add(&customSerializeMiddleware{}, middleware.After)
                    })
                }

                // Apply options to the GetItem call
                out, err := client.GetItem(ctx, in, customMiddleware)
                if err != nil {
                    return err
                }
                writeVerbose(out)
            }
        }
    }
    d := time.Since(st)
    os.Stdout.WriteString(fmt.Sprintf("Total Time: %v, Avg Time: %v\n", d, d/iterations))
    return nil
}
```

输出：

```
failed to execute command: custom middleware through APIOptions is not supported in DAX client
exit status 1
```