优化DynamoDB大规模数据查询：理解限制与高效策略

import software.amazon.awssdk.services.dynamodb.DynamoDbClient;
import software.amazon.awssdk.services.dynamodb.model.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class DynamoDBPaginator {

    private final DynamoDbClient ddbClient;
    private final String tableName;

    public DynamoDBPaginator(DynamoDbClient ddbClient, String tableName) {
        this.ddbClient = ddbClient;
        this.tableName = tableName;
    }

    /**
     * 分页查询示例：获取特定航班所有商务舱乘客。
     * 假设分区键是 'flightId'，排序键是 'bookingDate'，且 'ticketClass' 是属性。
     *
     * @param flightId 要查询的航班ID
     * @return 符合条件的乘客列表
     */
    public List<Map<String, AttributeValue>> fetchBusinessClassPassengers(String flightId) {
        List<Map<String, AttributeValue>> allPassengers = new ArrayList<>();
        Map<String, AttributeValue> lastEvaluatedKey = null;

        do {
            Map<String, AttributeValue> expressionAttributeValues = new HashMap<>();
            expressionAttributeValues.put(":flightIdVal", AttributeValue.builder().s(flightId).build());
            expressionAttributeValues.put(":ticketClassVal", AttributeValue.builder().s("BUSINESS").build());

            QueryRequest.Builder queryRequestBuilder = QueryRequest.builder()
                    .tableName(tableName)
                    .keyConditionExpression("flightId = :flightIdVal")
                    .filterExpression("ticketClass = :ticketClassVal") // 注意：filterExpression在数据检索后应用
                    .expressionAttributeValues(expressionAttributeValues)
                    .limit(100); // 每次请求的数据量，可以根据需求调整

            if (lastEvaluatedKey != null) {
                queryRequestBuilder.exclusiveStartKey(lastEvaluatedKey);
            }

            QueryResponse response = ddbClient.query(queryRequestBuilder.build());
            allPassengers.addAll(response.items());
            lastEvaluatedKey = response.lastEvaluatedKey();

            System.out.println("Fetched " + response.items().size() + " items. Total so far: " + allPassengers.size());

        } while (lastEvaluatedKey != null && !lastEvaluatedKey.isEmpty());

        return allPassengers;
    }

    /**
     * 分页扫描示例：获取表中所有乘客（不推荐用于生产环境大表）。
     *
     * @return 表中所有乘客列表
     */
    public List<Map<String, AttributeValue>> scanAllPassengers() {
        List<Map<String, AttributeValue>> allPassengers = new ArrayList<>();
        Map<String, AttributeValue> lastEvaluatedKey = null;

        do {
            ScanRequest.Builder scanRequestBuilder = ScanRequest.builder()
                    .tableName(tableName)
                    .limit(100); // 每次请求的数据量

            if (lastEvaluatedKey != null) {
                scanRequestBuilder.exclusiveStartKey(lastEvaluatedKey);
            }

            ScanResponse response = ddbClient.scan(scanRequestBuilder.build());
            allPassengers.addAll(response.items());
            lastEvaluatedKey = response.lastEvaluatedKey();

            System.out.println("Scanned " + response.items().size() + " items. Total so far: " + allPassengers.size());

        } while (lastEvaluatedKey != null && !lastEvaluatedKey.isEmpty());

        return allPassengers;
    }

    public static void main(String[] args) {
        // 实际应用中应配置合适的Region和凭证
        DynamoDbClient ddbClient = DynamoDbClient.builder()
                // .region(Region.AP_SOUTHEAST_1) // 根据实际情况配置
                .build();
        String tableName = "YourPassengerTableName"; // 替换为你的表名

        DynamoDBPaginator paginator = new DynamoDBPaginator(ddbClient, tableName);

        // 示例用法：查询特定航班的商务舱乘客
        // List<Map<String, AttributeValue>> businessPassengers = paginator.fetchBusinessClassPassengers("FLIGHT123");
        // System.out.println("Business class passengers fetched: " + businessPassengers.size());

        // 示例用法：扫描所有乘客 (不推荐用于生产环境大表)
        // List<Map<String, AttributeValue>> allPassengers = paginator.scanAllPassengers();
        // System.out.println("All passengers scanned: " + allPassengers.size());

        ddbClient.close();
    }
}