将 await 与异步数据库调用一起使用有什么好处 [英] What is the benefit to using await with an async database call

问题描述

我只是在查看默认的 MVC5 项目以及它如何在控制器中使用异步.

I am just looking at the default MVC5 project and how it uses async in the controllers.

我想知道异步在这里比简单地使用同步调用有什么好处:

I would like to know what benefit async provides here over simply using synchronous calls:

    [HttpPost]
    [ValidateAntiForgeryToken]
    public async Task<ActionResult> Disassociate(string loginProvider, string providerKey)
    {
        ManageMessageId? message = null;

        //why use an async database call here with await instead of just using a synchronous one?
        IdentityResult result = await UserManager.RemoveLoginAsync(User.Identity.GetUserId(), new UserLoginInfo(loginProvider, providerKey));
        if (result.Succeeded)
        {
            message = ManageMessageId.RemoveLoginSuccess;
        }
        else
        {
            message = ManageMessageId.Error;
        }
        return RedirectToAction("Manage", new { Message = message });
    }

我错过了什么?

这是否会在此处发生的等待类型中提供某种性能优势?

Does this provide some kind of performance benefit in the type of wait that will occur here?

推荐答案

在服务器端(例如，ASP.NET MVC)，您所做的任何 I/O(例如，数据库)都应该异步完成.这会在 I/O 进行中释放请求线程.

On the server side (e.g., ASP.NET MVC), any I/O you do (e.g., databases) should be done asynchronously. This frees up the request thread for the time that the I/O is in flight.

所以，当RemoveLoginAsync向数据库发送它的SQL时，它返回一个未完成的任务，当请求命中await时，它返回请求线程给线程池.之后，当DB操作完成时，从线程池中取出一个请求线程，用于继续请求.

So, when the RemoveLoginAsync sends its SQL to the database, it returns an incomplete task, and when the request hits the await, it returns the request thread to the thread pool. Later, when the DB operation completes, a request thread is taken from the thread pool and used to continue the request.

最终结果是可扩展性，因为(至少在 99.9% 的情况下)任务比线程可扩展性更好.但是，如果您的数据库只是一个服务器并且所有请求都访问数据库，那么这并没有太大的优势，因为在这种情况下，您的可扩展性瓶颈是数据库服务器，而不是 Web 服务器.

The end result is scalability, because (in the 99.9% case at least) tasks scale better than threads. However, there isn't a big advantage if your database is just a single server and all requests hit the db, because your scalability bottleneck in that scenario is the db server, not the web server.

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