I’m happy with the progress I have made so far. I have a lot of the groundwork laid, but it will still be a few weeks before the initial version is ready to be published. Here’s the summary…

Finished Work

1. Domain purchased
2. Database Schema tentatively complete
3. Website project created
4. Simple Logo produced
5. Default / login screen working
6. Error handling in place, notifications of problems being routed correctly
7. Maintenance mode working
8. Dashboard “shell” built
9. Accounts summary pane on dashboard finished

Needed Before Release

1. A place to host the website and database (being worked out, should have this soon)
2. Make a decision on whether to use some third party controls and which ones
3. CRUD (Create, Read, Update, & Delete) for:
   • Accounts
   • Recurrences
   • Manual Entry
   • Recurrence adjustments
4. Balance calculations
5. Account projections
6. Graphical visuals
7. Data export

I already have the database all laid out on paper, and I will make database diagrams and code samples available as I finish them. At some point I may be forced to stop posting source code for the sake of security, but until I start collecting sensitive data (right now the data I track can’t be tied to anyone or any actual accounts), I will continue to post code here.

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.

My Research
On the website in question, I use LINQ-to-SQL heavily to perform data operations. Naturally, I suspected that I wasn’t disposing of my DataContext objects correctly, causing me to exceed the number of connections available in the pool. After doing a little research on the subject, I read in several articles (some by folks who are much more knowledgeable than myself) that I shouldn’t have to dispose of them. They all said the following code is just fine:

CORDataContext mcon = new CORDataContext();
COR_Employee emp = mcon.COR_Employees.FirstOrDefault();

In fact, I should be able to put that into an infinite loop and never get the exception I was encountering. According to the experts, LINQ is not only smart enough to automatically open and close the connection for me, but also smart enough to dispose of the object when I’m done. No need for a “using” around my code or even a Connection.Close().

An Exception to the Rule

I noticed, though, that my code was slightly different. In my specific setup, I have a central database and a LOT of other databases I might want to connect to. So, to take advantage of connection pooling more, I always connect to the central database first and change to whatever catalog I need to access. In doing so, it is necessary to manually open the connection, like the following:

CORDataContext mcon = new CORDataContext();mcon.Connection.Open(); mcon.Connection.ChangeDatabase("OtherDB");
COR_Employee emp = mcon.COR_Employees.FirstOrDefault();

My Testing

I began to theorize that manually opening the connection in this way keeps the connection alive after I’ve run my query. I confirmed the belief by trying to run the following code:

for (int i = 0; i < 1000; i++) {

    CORDataContext mcon = new CORDataContext();
    COR_Employee emp = mcon.COR_Employees.FirstOrDefault();
    mcon.Connection.Open();
    mcon.Connection.ChangeDatabase("OtherDB");

    Console.WriteLine("" + (i + 1) + " / 1000");
}

I got the exception after 230 or so connections. By default there are 100 connections available in the pool, but the garbage collector kicked in and helped give me a buffer before I ran out. So, from that I can conclude that manually opened DataContext connections will stay open until the connection is closed or the DataContext is disposed.

The Solution

Once I fully understood the problem, the fix was common sense:

for (int i = 0; i < 1000; i++) {

    using (CORDataContext mcon = new CORDataContext()) {
        COR_Employee emp = mcon.COR_Employees.FirstOrDefault();
        mcon.Connection.Open();
        mcon.Connection.ChangeDatabase("OtherDB");

        Console.WriteLine("" + (i + 1) + " / 1000");
    }
}

Adding a “using” to automatically dispose of my DataContext did the trick, and this loop now finishes in about 3 seconds (even with the overhead of writing to the console). I hope this helps someone else, because it’s been plaguing me for weeks!

In your class definition you need to implement the interface System.Web.SessionState.IRequiresSessionState. Once you’ve done that you’ll find yourself magically able to use session once more.

Deriving from System.Web.UI.Page 
A quick and dirty way to get a maintenance window up for your site is to write a base page (derived from System.Web.UI.Page) that all of your pages derive from. That way you can specify things to happen on multiple pages from one central location. So let’s say I have BasePage.cs in my App_Code folder. I can override the OnPreInit() method to check to see whether I’m supposed to be in maintenance mode or not. If the site is supposed to be “down” I will redirect the user to a page that will say the site is down for maintenance. For now I will just be checking a flag I’ve set in app settings.

protected override void OnPreInit(EventArgs e) {
    base.OnPreInit(e);
    if (ConfigurationManager.AppSettings["MaintenanceMode"].ToUpper() == "TRUE") {
        if (Request.Url.AbsolutePath.ToLower() != "/maintenance.aspx") {
            Response.Redirect("Maintenance.aspx");
        }
    }
}

Using an HttpModule

An alternate way to add code that checks for maintenance (and is less work if you have medium-to-large sized site OR multiple sites that need to use the same maintenance code) is to place it in an HttpModule and add the module to web.config. I personally think the HttpModule is perfectly suited to solving this problem. Checking for maintenance is typically something that is separate from most other things, so it makes sense to modularize it as much as possible. It’s just good form! Here’s my module code:

public class MaintenanceModule : IHttpModule
{
    #region IHttpModule Members

    public void Dispose() {

    }

    public void Init(HttpApplication context) {
        context.BeginRequest +=new EventHandler(context_BeginRequest);
    }

    public void context_BeginRequest(object sender, EventArgs e) {        if (ConfigurationManager.AppSettings["MaintenanceMode"] == "TRUE") {             if (Request.Url.AbsolutePath.ToLower() != "/maintenance.aspx") {                 Response.Redirect("Maintenance.aspx");             }         }
    }
    #endregion
}

And here is my web.config entry (added to the httpModules section in system.web for local use; put it in the modules section of system.webserver for IIS to pick it up):

<add name="MaintenanceModule" type="MaintenanceModule" />

Scheduling Maintenance Ahead of Time

I like to give my users several days’ notice before I bring a site down for maintenance, so I do two things to accomplish that. First, I keep a table called MaintenanceSchedule that I can put a start time, end time, public message, and private message into. Then, on pages where I want to notify users of the upcoming maintenance, I check the table for maintenance periods that haven’t yet begun.

string connectionString =
    ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;

using (SqlConnection con = new SqlConnection(connectionString)) {
    con.Open();
    using (SqlCommand com = con.CreateCommand()) {
        com.CommandText = "GetNextMaintenancePeriod";
        com.CommandType = CommandType.StoredProcedure;

        using (SqlDataReader sdr = com.ExecuteReader()) {
            if (sdr.Read()) {
                DateTime start = sdr.GetDateTime(1);
                DateTime end = sdr.GetDateTime(2);

                litUpcomingMaintenance.Text =
                    "<strong>Alert!</strong> "
                    + "This site will be going down for maintenance from "
                    + start.ToString() + " until " + end.ToString() + ".";
            }
            else {
                // throw an exception to show the default message.
                throw new Exception("No maintenance period found...");
            }
        }
    }
}

This method also allows me to put a more specific message out when the site is actually being worked on as well as a way to keep a record of when past maintenance periods occurred.

string connectionString =
    ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;

try {
    using (SqlConnection con = new SqlConnection(connectionString)) {
        con.Open();
        using (SqlCommand com = con.CreateCommand()) {
            com.CommandText = "GetCurrentMaintenancePeriod";
            com.CommandType = CommandType.StoredProcedure;

            using (SqlDataReader sdr = com.ExecuteReader()) {
                if (sdr.Read()) {
                    DateTime start = sdr.GetDateTime(1);
                    DateTime end = sdr.GetDateTime(2);
                    string message = sdr.GetString(3);

                    litMaintenance.Text =
                        "This site is currently undergoing maintenance. "
                        + "Maintenance is expected to start at "
                        + start.ToString() + " and end at " + end.ToString()
                        + ".<br/><br/>" + message;
                }
                else {
                    // throw an exception to show the default message.
                    throw new Exception("No maintenance period found...");
                }
            }
        }
    }
}
catch (Exception ex) {
    // This is in case my database goes down during the maintenance period.
    litMaintenance.Text = "This site is currently undergoing maintenance."
        + " Please try again later.";
}

I’ll also alter my base page to automatically take the site down when maintenance is scheduled to begin.

string connectionString =
    ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;

if (Request.Url.AbsolutePath.ToLower() != "/maintenance.aspx") {
    using (SqlConnection con = new SqlConnection(connectionString)) {
        con.Open();
        using (SqlCommand com = con.CreateCommand()) {
            com.CommandText = "GetCurrentMaintenancePeriod";
            com.CommandType = CommandType.StoredProcedure;

            using (SqlDataReader sdr = com.ExecuteReader()) {
                if (sdr.Read()) {
                    Response.Redirect("Maintenance.aspx");
                }
            }
        }
    }
}

Code Sample

I’ve included a sample website with a SQL script to show how all the pieces fit together. Just download the files, run the SQL against your database, open the website (I used Microsoft Visual Web Developer 2008 Express Edition), and put your connection string into the web.config. Then, add some rows into the MaintenanceSchedule table and run the site to see how it all works.

Download Sample Code (.zip)