如何在 Gatling 中注入恒定数量的用户？

Question

我不清楚如何在 Gatling 中控制封闭的工作负载模型。

如果我使用constantConcurrentUsers，像这样：

myScenario.inject(
    constantConcurrentUsers(40) during (2 minutes)
)

我认为这意味着活跃用户的数量将保持不变。但相反，我得到这样的报告：

用户数量不是恒定的，是我想要的数量的 3-5 倍。

不过，在控制台输出中，我可以看到某些内容是恒定的（这里有 4 个场景，每个场景都加载了 10 个恒定并发用户）：

但是总负载比我预期的要多得多。

我曾尝试过节流，结果很明显。在我的理解中，节流阀使并发活动请求的数量最大化（如果请求已发送但尚未响应，则该请求处于活动状态）。我定义了一些应该通过的请求，每次完成时 Gatling 都会发送一个新请求。并且由于响应时间之间没有太大差异，因此报告如下所示：

我想做同样的事情，但这样我就可以控制模拟的长度，而不是发送的请求总数。constantConcurrentUsers似乎正是我需要的东西，但它产生了意想不到的结果。我的油门模拟在大约1分钟内做了大约3000个请求，油门为50。同时，如果我设置50个并发用户1分钟，报告中发送了7000多个请求。在油门情况下，响应时间要短得多。所以节流模拟发送请求比并发用户模拟慢得多，但不是因为请求需要更多时间。

我知道活动用户和发送的请求是不一样的，它们constantConcurrentUsers控制用户数量，而节流控制请求。但是我所有的场景都只包含一个请求，所以我不明白结果之间的区别。

所以我的问题是：

• 当我使用时到底什么是常数constantConcurrentUsers？
• 我使用时如何计算请求数constantConcurrentUsers？
• 报告中的“活跃用户”与控制台输出中的“活跃用户”之间有什么关系？

我已经阅读了 Gatling 文档的这一部分，它真的很短，而且缺乏详细的描述。我还阅读了这篇文章，其中包含我从未在任何 Gatling 报告中看到的图表，并且没有回答我的问题。

感谢您的任何贡献。

Answer 1

I have found that the Cheatsheet describes each injection step most accurately. How you inject a constant number of users should be using constantConcurrentUsers which is described in the Cheatsheet as: "Maintain a constant number of concurrent users"

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As for your other questions:

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• What exactly is constant when I use constantConcurrentUsers?
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I believe Gatling does keep the number of concurrent users constant. The reason there are spikes in the number of requests is because one user can make multiple requests in a given timespan. As soon as the current request finishes for the user, a new request is fired by the same user. In your example, you had 40 users and your number of requests looks around 80, this indicates each user was achieving 2 requests a second (mean response time around 500ms?)

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• How is the number of requests calculated when I use constantConcurrentUsers?
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As per above, your concurrent users will just keep looping the request for the duration you set and it will not fire another until the current request provides a response. If your API is quick, your number of requests per second will be higher than your number of users.

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• What is the relation between "active users" in the report and "active" in the console output?
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This is actually where I am a bit unsure :/ I set have 10 constantConcurrentUsers in my test, and console shows similar to yours, but my report shows between 10-75 active users over time\n

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However, this Reports page in Gatling docs sheds some light:

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\xe2\x80\x9cActive users\xe2\x80\x9d is neither \xe2\x80\x9cconcurrent users\xe2\x80\x9d or \xe2\x80\x9cusers arrival rate\xe2\x80\x9d.\n It\xe2\x80\x99s a kind of mixed metric that serves for both open and closed\n workload models and that represents \xe2\x80\x9cusers who were active on the\n system under load at a given second\xe2\x80\x9d.

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It\xe2\x80\x99s computed as:

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(number of alive users at previous second)\n + (number of users that were started during this second)\n - (number of users that were terminated during previous second)

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