[转载] AZURE SQL数据库"DTU百分比"度量标准
DTU是服务层性能的度量单位，是几个数据库特征的总结。 每个服务层都有一定数量的DTU分配给它，作为比较一层与另一层性能水平的简单方法。
数据库吞吐量单元（DTU）： DTU提供了一种方式来描述基本，标准和高级数据库性能级别的相对容量。 DTU基于CPU，内存，读取和写入的混合度量。 随着DTU的增加，性能水平提供的功率也会增加。 例如，具有5个DTU的性能等级比具有1个DTU的性能等级高5倍。 最大DTU配额适用于每台服务器。
Database Throughput Unit (DTU): DTUs provide a way to describe the relative capacity of a performance level of Basic, Standard, and Premium databases. DTUs are based on a blended measure of CPU, memory, reads, and writes. As DTUs increase, the power offered by the performance level increases. For example, a performance level with 5 DTUs has five times more power than a performance level with 1 DTU. A maximum DTU quota applies to each server.
DTU限额适用于服务器，而不是单个数据库，每个服务器最多有1600个DTU。 DTU％是特定数据库使用的单位的百分比，看起来这个数字可以超过服务层（我假定服务器的限制）的DTU等级的100％。 此百分比数字旨在帮助您select适当的服务层。
例如，如果您的DTU消耗显示80％的值，则表明它正在以S2数据库将具有的限制的80％的比率消耗DTU。 如果您在此视图中看到的值大于100％，则意味着您需要大于S2的性能级别。
举一个例子，假设你看到一个百分比值为300％。 这告诉你，你使用的资源比S2中多出三倍。 要确定合理的起始大小，请将S2（50个DTU）中可用的DTU与下一个更高大小（P1 = 100个DTU，或者S2的200％，P2 = 200个DTU或S2的400％）进行比较。 因为你是S2的300％，所以你想从P2开始并重新testing。
For example, if your DTU consumption shows a value of 80%, it indicates it is consuming DTU at the rate of 80% of the limit an S2 database would have. If you see values greater than 100% in this view it means that you need a performance tier larger than S2.
As an example, let’s say you see a percentage value of 300%. This tells you that you are using three times more resources than would be available in an S2. To determine a reasonable starting size, compare the DTUs available in an S2 (50 DTUs) with the next higher sizes (P1 = 100 DTUs, or 200% of S2, P2 = 200 DTUs or 400% of S2). Because you are at 300% of S2 you would want to start with a P2 and re-test.
在这个文档中提到，DTU百分比是由这个查询决定的：
SELECT end_time, (SELECT Max(v) FROM (VALUES (avg_cpu_percent), (avg_data_io_percent), (avg_log_write_percent)) AS value(v)) AS [avg_DTU_percent] FROM sys.dm_db_resource_stats; 看起来像avg_cpu_percent ， avg_data_io_percent和avg_log_write_percent
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