扫描DynamoDB表未返回数据 [英] Scan DynamoDB table is not returning data

问题描述

我正在尝试从dynamodb数据库表中扫描失败的令牌计数，而没有任何索引。它从数据库返回0。我怀疑它没有扫描完整的数据库。下面是我的方法和 dynamoDBClient 工作条件之一，它具有连接详细信息。我只在此处发布扫描查询部分

I am trying to scan failed token counts from dynamodb database table without any indexes. It is returning 0 from the database. I doubt it is not scanning complete database. Below is my method and the dynamoDBClient working condition one and it has connection details. I am posting here only the scan query part

public int getFailedAuthStatusCount() {

    Map<String,String> expressionAttributesNames = new HashMap<>();
      expressionAttributesNames.put("#status","auth_status");

    Map<String, AttributeValue> expressionAttributeValues = new HashMap<String, AttributeValue>();
    expressionAttributeValues.put(":val", new AttributeValue().withS("FAIL"));

    ScanRequest scanRequest = new ScanRequest()
              .withTableName("Token")
              .withFilterExpression("#status = :val")
              .withExpressionAttributeNames(expressionAttributesNames)
              .withExpressionAttributeValues(expressionAttributeValues);
    ScanResult scanResult = dynamoDBClient.scan(scanRequest); //client is working fine.
    return scanResult.getCount();
  }

这是响应。

{Items: [],Count: 0,ScannedCount: 1456,LastEvaluatedKey: {GUID={S: 0c4b281e6f9290c0fb3bf13f28c88fd,}, VENDOR={S: DELL,}},}

我的请求出了什么问题？

what is wrong with my request?

推荐答案

您的请求没有问题。扫描时，您必须继续使用先前的 LastEvaluatedKey 作为下一个请求的 ExclusiveStartKey 重新提交请求，直到不再收到响应中的 LastEvaluatedKey 。

Nothing is wrong with your request. When scanning, you have to continue resubmitting the request with the prior LastEvaluatedKey as the next request's ExclusiveStartKey until you no longer receive a LastEvaluatedKey in the response.

您的第一个请求仅评估第一个 ScannedCount：表格中有1456 个项目（≈1MB数据）。

Your first request is only evaluating the first ScannedCount: 1456 items in the table (≈ 1MB of data).

请参见 https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Scan.html#Scan.Pagination

在所有数据库环境中，表扫描都是缓慢且昂贵的。这就是索引很重要的关键原因。 DynamoDB由于可用的底层API而使这一点更加明显。

Table scans are slow and expensive in all database environments. That's a key reason why indexes are important. DynamoDB makes this more apparent because of the low-level API that's available.

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