In asp.net-mvc, what is the correct way to do expensive operations without impacting other users?

Question

I asked this question about 5 years ago around how to "offload" expensive operations where the users doesn't need to wait for (such as auditng, etc) so they get a response on the front end quicker.

I now have a related but different question. On my asp.net-mvc, I have build some reporting pages where you can generate excel reports (i am using EPPlus) and powerpoint reports (i am using aspose.slides). Here is an example controller action:

    public ActionResult GenerateExcelReport(FilterParams args)
    {
        byte[] results = GenerateLargeExcelReportThatTake30Seconds(args);
        return File(results, @"application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml", "MyReport.xlsx");
    }

The functionality working great but I am trying to figure out if these expensive operations (some reports can take up to 30 seconds to return) are impacting other users. In the previous question, I had an expensive operation that the user DIDN"T have to wait for but in this case he does have to wait for as its a syncronoous activity (click Generate Report and expectation is that users get a report when its finished)

In this case, I don't care that the main user has to wait 30 seconds but i just want to make sure I am not negatively impacting other users because of this expensive operation, generating files, etc

Is there any best practice here in asp.net-mvc for this use case ?

Answer 1

You can try combination of Hangfire and SignalR. Use Hangfire to kickoff a background job and relinquish the http request. And once report generation is complete, use SignalR to generate a push notification.

SignalR notification from server to client

Alternate option is to implement a polling mechanism on client side. Send an ajax call to enque a hangfire job to generate the report. And then start polling some api using another ajax call that provides status and as soon report is ready, retrieve it. I prefer to use SignalR rather than polling.

If the report processing is impacting the performance on the web server, offload that processing to another server. You can use messaging (ActiveMQ or RabbitMQ or some other framework of your choice) or rest api call to kick off report generation on another server and then again use messaging or rest api call to notify report generation completion back to the web server, finally SignalR to notify the client. This will let the web server be more responsive.

UPDATE Regarding your question

Is there any best practice here in asp.net-mvc for this use case

You have to monitor your application overtime. Monitor both Client side as well as server side. There are few tools you can rely upon such as newrelic, app dynamics. I have used newrelic and it has features to track issues both at client browser as well as server side. The names of the product are "NewRelic Browser" and "NewRelic Server". I am sure there are other tools that will capture similar info.

Analyze the metrics overtime and if you see any anomalies then take appropriate actions. If you observe server side CPU and memory spikes, try capturing metrics on client side around same timeframe. On client side if you notice any timeout issues, connection errors that means your application users are unable to connect to your app while the server is doing some heavy lifting. Next try to Identify server side bottlenecks. If there is not enough room to performance tune the code, then go thru some server capacity planning exercise and figure out how to further scale your hardware or move the background jobs out of the web servers to reduce load. Just capturing metrics using these tools may not be enough, you may have to instrument (log capturing) your application to capture additional metrics to properly monitor application health.

Here you can find some information about capacity planning for .net application from Microsoft.

-Vinod.

Answer 2

Queue the jobs in a table, and have a background process poll that table to decide which Very Large Job needs to run next. Your web client would then need to poll the server to determine when the job is complete (potentially by checking a flag in the database, but there are other methods.) This guarantees that you won't have more than one (or however many you decide is appropriate) of these expensive processes running at a time.

Hangfire and SignalR can help you here, but a queueing mechanism is really necessary to avoid major disruption when, say, five users request this same process at the same time. The approaches mentioned that fire off new threads or background processes don't appear to provide any mechanism for minimizing processor / memory consumption to avoid disrupting other users due to consuming too many resources.

Answer 3

You need to monitor your application users to know if other users are being affected e.g. by recording response times

If you find that this is affecting other users, you need to run the task in another process, potentially on another machine. You can use the library Hangfire to achieve this.

Answer 4

Using that answer, you can declare a Task with low priority

lowering priority of Task.Factory.StartNew thread

 public ActionResult GenerateExcelReport(FilterParams args)
 {
     byte[] result = null;
     Task.Factory.StartNew(() =>
     {
        result =  GenerateLargeExcelReportThatTake30Seconds(args);
     }, null, TaskCreationOptions.None, PriorityScheduler.BelowNormal)
      .Wait();

     return File(result, @"application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml", "MyReport.xlsx");
 }

Answer 5

I believe a tool/library such as Hangfire is what your looking for. First, it'll allows for you to specify a task run on a background thread (in the same application/process). Using various techniques, such as SignalR allows for real-time front-end notification.

However, something I set up after using Hangfire for nearly a year was splitting our job processing (and implementation) to another server using this documentation. I use an internal ASP.NET MVC application to process jobs on a different server. The only performance bottleneck, then, is if both servers use the same data store (e.g. database). If your locking the database, the only way around it is to minimize the locking of said resource, regardless if the methodology you use.

I use interfaces to trigger jobs, stored in a common library:

public interface IMyJob
{
    MyJobResult Execute( MyJobSettings settings );
}

And, the trigger, found in the front-end application:

//tell the job to run
var settings =  new MyJobSettings();
_backgroundJobClient.Enqueue<IMyJob>( c => c.Execute( settings ) );

Then, on my background server, I write the implementation (and hook in it into the Autofac IOC container I'm using):

public class MyJob : IMyJob
{
    protected override MyJobResult Running( MyJobSettings settings )
    {
         //do stuff here
    }
}

I haven't messed too much with trying to get SignalR to work across the two servers, as I haven't run into that specific use case yet, but it's theoretically possible, I imagine.

Answer 6

You need to use async and await of C#.

From your question I figured that you are just concerned with the fact that the request can be taking more resources than it should, instead of with scalability. If that's the case, make your controller actions async, as well as all the operations you call, as long as they involve calls that block threads. e.g. if your requests go through wires or I/O operations, they will be blocking the thread without async (technically, you will, since you will wait for the response before continuing). With async, those threads become available (while awaiting for the response), and so they can potentially serve other requests of other users.

I assumed you are not wandering how to scale the requests. If you are, let me know, and I can provide details on that as well (too much to write unless it's needed).

Answer 7

These are all great ideas on how to move work out of the request/response cycle. But I think @leora simply wants to know whether a long-running request will adversely impact other users of an asp.net application.

The answer is no. asp.net is multi-threaded. Each request is handled by a separate worker thread.

Answer 8

In general it could be considered a good practice to run long running tasks in background and give some kind of notification to user when the job is done. As you probably know web request execution time is limited to 90 seconds, so if your long running task could exceed this, you have no choice but to run in some other thread/process. If you are using .net 4.5.2 you can use HostingEnvironment.QueueBackgroundWorkItem for running long running tasks in background and use SignalR to notify user when the task is finished the execution. In case that you are generating a file you can store it on server with some unique ID and send to user a link for downloading it. You can delete this file later (with some windows service for example).

As mentioned by others, there are some more advanced background task runners such as Hangfire, Quartz.Net and others but the general concept is the same - run task in backround and notify user when it is done. Here is some nice article about different oprions to run background tasks.