亚马逊DynamoDB需要很长时间才能获取最高延迟5-6秒的记录。

Question

pom.xml

<dependency>
    <groupId>com.amazonaws</groupId>
    <artifactId>aws-java-sdk-bom</artifactId>
    <version>1.11.256</version>
    <type>pom</type>
    <scope>import</scope>
</dependency>
<dependency>
    <groupId>com.amazonaws</groupId>
    <artifactId>aws-java-sdk-dynamodb</artifactId>
</dependency>

客户代码

public static AmazonDynamoDB getDynamoDBClient() {
        return AmazonDynamoDBClientBuilder.standard().withRegion("ap-southeast-1").build();
}

现在，我正在尝试执行一个记录很少的普通查询，但是获取结果需要很长时间。

这是它第一次在5-6秒内对多个请求获取记录，减少了一半。2-3秒仍然是很长的时间，因为只取几个项目。

已经使用不同的客户端配置(连接超时、请求超时、重试等)检查了dynamo DB的调优。但没有给出预期的结果。也检查了SDK 2 URLConnectionHTTPClient配置，但结果也是一样的。

一个可能的原因可能是dynamo客户端的凭据获取时间，但在java中没有任何凭据缓存引用。有人能建议可能的配置来改善这个延迟吗？

Answer 1

您正在使用一个非常老的API，不再是最佳实践。要在Java中使用最佳实践，请使用AWS v2。

AWSSDKforJava2.x是版本1.x代码库的主要重写版本。它构建在Java 8+之上，并添加了几个经常被请求的特性。这包括对非阻塞I/O的支持，以及在运行时插入不同的HTTP实现的能力。

v2的POM是：

 <dependency>
  <groupId>software.amazon.awssdk</groupId>
  <artifactId>bom</artifactId>
  <version>2.17.190</version>
  <type>pom</type>
  <scope>import</scope>
 </dependency>

要使用v2检索记录，您有三个选择。

• 使用DynamoDbClient。
• 使用增强的客户端(将Java对象映射到表)
• 使用PartiQL (使用类似于SQL的语法)

我会向你展示所有的方法。所有的例子都可以在亚马逊Github回购公司中找到。

使用DynamoDbClient

守则是：

package com.example.dynamodb;

// snippet-start:[dynamodb.java2.get_item.import]
import software.amazon.awssdk.auth.credentials.ProfileCredentialsProvider;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.dynamodb.model.DynamoDbException;
import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import software.amazon.awssdk.services.dynamodb.model.AttributeValue;
import software.amazon.awssdk.services.dynamodb.model.GetItemRequest;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
// snippet-end:[dynamodb.java2.get_item.import]


/**
 * Before running this Java V2 code example, set up your development environment, including your credentials.
 *
 * For more information, see the following documentation topic:
 *
 * https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/get-started.html
 *
 * To get an item from an Amazon DynamoDB table using the AWS SDK for Java V2, its better practice to use the
 * Enhanced Client, see the EnhancedGetItem example.
 */
public class GetItem {

    public static void main(String[] args) {

        final String usage = "\n" +
                "Usage:\n" +
                "    <tableName> <key> <keyVal>\n\n" +
                "Where:\n" +
                "    tableName - The Amazon DynamoDB table from which an item is retrieved (for example, Music3). \n" +
                "    key - The key used in the Amazon DynamoDB table (for example, Artist). \n" +
                "    keyval - The key value that represents the item to get (for example, Famous Band).\n" ;

        if (args.length != 3) {
            System.out.println(usage);
            System.exit(1);
        }

        String tableName = "Customer" ; //args[0];
        String key = "id" ; //args[1];
        String keyVal = "id101" ; //args[2];
        System.out.format("Retrieving item \"%s\" from \"%s\"\n", keyVal, tableName);

        ProfileCredentialsProvider credentialsProvider = ProfileCredentialsProvider.create();
        Region region = Region.US_EAST_1;
        DynamoDbClient ddb = DynamoDbClient.builder()
                .credentialsProvider(credentialsProvider)
                .region(region)
                .build();

        getDynamoDBItem(ddb, tableName, key, keyVal);
        ddb.close();
    }

    // snippet-start:[dynamodb.java2.get_item.main]
    public static void getDynamoDBItem(DynamoDbClient ddb,String tableName,String key,String keyVal ) {

        HashMap<String,AttributeValue> keyToGet = new HashMap<>();
        keyToGet.put(key, AttributeValue.builder()
                .s(keyVal).build());

        GetItemRequest request = GetItemRequest.builder()
                .key(keyToGet)
                .tableName(tableName)
                .build();

        try {
            Map<String,AttributeValue> returnedItem = ddb.getItem(request).item();

            if (returnedItem != null) {
                Set<String> keys = returnedItem.keySet();
                System.out.println("Amazon DynamoDB table attributes: \n");

                for (String key1 : keys) {
                    System.out.format("%s: %s\n", key1, returnedItem.get(key1).toString());
                }
            } else {
                System.out.format("No item found with the key %s!\n", key);
            }
        } catch (DynamoDbException e) {
            System.err.println(e.getMessage());
            System.exit(1);
        }
    }
    // snippet-end:[dynamodb.java2.get_item.main]
}

增强客户端

守则是：

package com.example.dynamodb;

// snippet-start:[dynamodb.java2.mapping.getitem.import]
import software.amazon.awssdk.auth.credentials.ProfileCredentialsProvider;
import software.amazon.awssdk.enhanced.dynamodb.DynamoDbEnhancedClient;
import software.amazon.awssdk.enhanced.dynamodb.DynamoDbTable;
import software.amazon.awssdk.enhanced.dynamodb.Key;
import software.amazon.awssdk.enhanced.dynamodb.TableSchema;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import software.amazon.awssdk.services.dynamodb.model.DynamoDbException;
// snippet-end:[dynamodb.java2.mapping.getitem.import]

/*
 * Before running this code example, create an Amazon DynamoDB table named Customer with these columns:
 *   - id - the id of the record that is the key
 *   - custName - the customer name
 *   - email - the email value
 *   - registrationDate - an instant value when the item was added to the table
 *
 * Also, ensure that you have set up your development environment, including your credentials.
 *
 * For information, see this documentation topic:
 *
 * https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/get-started.html
 */

public class EnhancedGetItem {

    public static void main(String[] args) {

        ProfileCredentialsProvider credentialsProvider = ProfileCredentialsProvider.create();
        Region region = Region.US_EAST_1;
        DynamoDbClient ddb = DynamoDbClient.builder()
                .credentialsProvider(credentialsProvider)
                .region(region)
                .build();

        DynamoDbEnhancedClient enhancedClient = DynamoDbEnhancedClient.builder()
                .dynamoDbClient(ddb)
                .build();

        getItem(enhancedClient);
        ddb.close();
    }

    // snippet-start:[dynamodb.java2.mapping.getitem.main]
    public static void getItem(DynamoDbEnhancedClient enhancedClient) {

        try {
            DynamoDbTable<Customer> table = enhancedClient.table("Customer", TableSchema.fromBean(Customer.class));
            Key key = Key.builder()
                    .partitionValue("id120")
                    .build();

            // Get the item by using the key.
            Customer result = table.getItem(r->r.key(key));
            System.out.println("******* The description value is "+result.getCustName());

        } catch (DynamoDbException e) {
            System.err.println(e.getMessage());
            System.exit(1);
        }
    }
    // snippet-end:[dynamodb.java2.mapping.getitem.main]
}

PartiQL

代码是

public static void getItem(DynamoDbClient ddb) {

        String sqlStatement = "SELECT * FROM MoviesPartiQ where year=? and title=?";
        List<AttributeValue> parameters = new ArrayList<>();
        AttributeValue att1 = AttributeValue.builder()
                .n("2012")
                .build();

        AttributeValue att2 = AttributeValue.builder()
                .s("The Perks of Being a Wallflower")
                .build();

        parameters.add(att1);
        parameters.add(att2);

        try {
            ExecuteStatementResponse response = executeStatementRequest(ddb, sqlStatement, parameters);
            System.out.println("ExecuteStatement successful: "+ response.toString());

        } catch (DynamoDbException e) {
            System.err.println(e.getMessage());
            System.exit(1);
        }
    }

所有这些方法都推荐在AWS V1上使用。如果您不熟悉V2 API --包括creds和设置您的环境，请参见：

开发者指南-AWSSDKforJava2.x

Answer 2

这是它第一次在5-6秒内对多个请求获取记录，减少了一半。2-3秒仍然是很长的时间，因为只取几个项目。

这是预期的，即使在生产发电机，因为您第一次获取以下操作序列发生：-

1. 查找来自路由表的请求数据所属的分区ID。
2. 缓存分区的密钥。
3. 然后引用用于获取数据的分区。

正如您在步骤2中看到的那样，在下一次请求发生时，从缓存中获取分区id，从而减少延迟。(一旦我有了它，就会分享它的来源)

有人能建议可能的配置来改善这个延迟吗？

此外，请不要使用本地发电机进行性能基准测试，因为它内部使用SQLite，即SQL存储。参考：- https://www.dbi-services.com/blog/aws-dynamodb-local/#:~:text=Yes%2C%20this%20NoSQL%20database%20is,Local%20engine%2C%20embedded%20in%20Java。