Connection leak (C#/ADO.NET) even though SqlConnection created with using

问题

I have a program that loads a large quantity of data (~800K-1M rows per iteration) in a Task running on the threadpool (see offending code sample below); no more than 4 tasks running concurrently. This is the only place in the program that a connection is made to this database. When running the program on my laptop (and other coworkers identical laptops), the program functions perfectly. However, we have access to another workstation via remote desktop that is substantially more powerful than our laptops. The program fails about 1/3 to 1/2 of the way through its list. All of the tasks return an exception.

The first exception was: "Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached." I've tried googling, binging, searching on StackOverflow, and banging my head against the table trying to figure out how this can be the case. With no more than 4 tasks running at once, there shouldn't be more than 4 connections at any one time.

In response to this, I tried two things: (1) I added a try/catch around the conn.Open() line that would clear the pool if InvalidOperationException appears--that appeared to work [didn't let it run all the way through, but got substantially past where it did before], but at the cost of performance. (2) I changed ConnectionTimeout to be 30 seconds instead of 15, which did not work (but let it proceed a little more). I also tried at one point to do ConnectRetryInterval=4 (mistakenly choosing this instead of ConnectRetryCount)--this let to a different error "The maximum number of requests is 4,800", which is strange because we still shouldn't be anywhere near 4,800 requests or connections.

In short, I'm at a loss because I can't figure out what is causing this connection leak only on a higher speed computer. I am also unable to get Visual Studio on that computer to debug directly--any thoughts anyone might have on where to look to try and resolve this would be much appreciated.

(Follow-up to c# TaskFactory ContinueWhenAll unexpectedly running before all tasks complete)

private void LoadData()
    {
        SqlConnectionStringBuilder builder = new SqlConnectionStringBuilder();
        builder.DataSource = "redacted";
        builder.UserID = "redacted";
        builder.Password = "redacted";
        builder.InitialCatalog = "redacted";
        builder.ConnectTimeout = 30;

        using (SqlConnection conn = new SqlConnection(builder.ConnectionString))
        {
            //try
            //{
            //    conn.Open();
            //} catch (InvalidOperationException)
            //{
            //    SqlConnection.ClearPool(conn);
            //    conn.Open();
            //}
            conn.Open();


            string monthnum = _monthsdict.First((x) => x.Month == _month).MonthNum;
            string yearnum = _monthsdict.First((x) => x.Month == _month).YearNum;

            string nextmonthnum = _monthsdict[Array.IndexOf(_monthsdict, _monthsdict.First((x) => x.Month == _month))+1].MonthNum;
            string nextyearnum = _monthsdict[Array.IndexOf(_monthsdict, _monthsdict.First((x) => x.Month == _month)) + 1].YearNum;

            SqlCommand cmd = new SqlCommand();

            cmd.Connection = conn;

            cmd.CommandText = @"redacted";
            cmd.Parameters.AddWithValue("@redacted", redacted);
            cmd.Parameters.AddWithValue("@redacted", redacted);
            cmd.Parameters.AddWithValue("@redacted", redacted);
            cmd.CommandTimeout = 180;

            SqlDataReader reader = cmd.ExecuteReader();
            while(reader.Read())
            {
                Data data = new Data();

                int col1 = reader.GetOrdinal("col1");
                int col2 = reader.GetOrdinal("col2");
                int col3 = reader.GetOrdinal("col3");
                int col4 = reader.GetOrdinal("col4");

                data.redacted = redacted;
                data.redacted = redacted;
                data.redacted = redacted;
                data.redacted = redacted;
                data.redacted = redacted;

                data.Calculate();
                _data.Add(data); //not a mistake, referring to another class variable
            }
            reader.Close();
            cmd.Dispose();
            conn.Close();
            conn.Dispose();
        }
    }

来源：https://stackoverflow.com/questions/61820220/connection-leak-c-ado-net-even-though-sqlconnection-created-with-using