IIS request won’t complete if “File Download” is open

asp.netiisiis-7

We have an ASP.NET application that returns image files to the user. When a user requests an image, the application sets the appropriate content information in the header, and returns the bytes. We have found that if the browser prompts the user to open or save the image, the IIS request will remain in "Send Response" state until the user chooses one of the prompt options.

The issue is that some users are not closing the prompt, which prevents the request from completing. Once this happens, other requests are also prevented from completing. Eventually, all the available threads are used up.

Is there any way to force IIS to forcefully kill a request after a timeout period? We've tried setting the "executionTimeout", but this doesn't have any effect, as the request thread isn't doing any work while it's waiting for the client to answer the prompt.

The connection timeout is set to the default of 120 seconds.

Best Answer

What is your Connection Timeout (HTTP KeepAlive timeout)?

Web Site > Connection Limits > Connection Timeout. The default is 120 seconds. (Not to be confused with the application pool timeout). Sometimes applications that use session affinity (sticky sessions) have a higher value for the timeout. Setting this too high would increase connections.

You should also ensure you have the latest http.sys hotfix installed, version 6.1.7601.21886.

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IIS: Request with unknown content-type denied

I was finally able to fix the problem by following the following guide at http://www.donnfelker.com/aspnet-mvc-iis7-and-bad-request/.

I added the following code to my web.config

<system.webServer>
  <httpErrors errorMode=”Detailed” />
</system.webserver>

Diagnose cause of long running requests in IIS 7.0

It look's like it's the common issue with the connection pooling and to many open connections. On your DAL you should have something like this (it doesn't matter if it is mssql or mysql):

(I'm assuming that you are using DataReader)

    /// <summary>
    /// Selects a single record from the Media table.
    /// </summary>
    public virtual Media Select(int mediaID)
    {
        SqlParameter[] parameters = new SqlParameter[]
        {
            new SqlParameter("@MediaID", mediaID)
        };

        using (SqlDataReader dataReader = SqlClientUtility.ExecuteReader(connectionStringName, CommandType.StoredProcedure, "MediaSelect", parameters))
        {
            if (dataReader.Read())
            {
                return MakeMedia(dataReader);
            }
            else
            {
                return null;
            }
        }
    }

using guarantee that SqlDataReader will be properly disposed. This is just a basic example but usually you should have (you may have) a common class for all DAL operation that provide connection helpers and that implements IDisposable. I recommend having a base class that all DAL classes derive from.

If DAL is not the issue I would recommend to digg deeper on the database using SQL Server Profiler to evaluate query executions.

You can also use SQL Server Monitor to check average execution times and un-closed connections. If your DAL has a problem you'll see a lot of pending/waiting connections.

Best Answer

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IIS: Request with unknown content-type denied

Diagnose cause of long running requests in IIS 7.0

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