Max pool size was reached

Have you ever encountered this error message on your application:

"Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occured because all pooled connections were in use and max pool size was reached."

This problem occurred most probably because of connection leak. Either the connection string do not close properly or consistently.

When you intend to close your database connection, you want to make sure that you are really closing it. The following code looks fine yet causes a connection leak:

     SqlConnection conn = new SqlConnection(myConnectionString);

      conn.Open();

      doSomething();

      conn.Close();      
           

If doSomething() throws an exception - conn will never get explicitly closed. Here is how this can be corrected:

     SqlConnection conn = new SqlConnection(myConnectionString);

      try

      {

            conn.Open();

            doSomething(conn);

      }

      finally

     {

            conn.Close();                 

      }

When returning a connection from a class method - make sure you cache it locally and call its Close method. The following code will leak a connection:

     OleDbCommand cmd new OleDbCommand(myUpdateQuery, getConnection());

      intres = cmd.ExecuteNonQuery();

     getConnection().Close(); // The connection returned from the first call to getConnection() is not being closed.

Instead of closing your connection, this line creates a new one and tries to close it.

Here are some solutions that you can try to solve the problem:

1) Check your application to make sure all database connections are closed when it is not needed.  ASP.NET is supposed to have garbage collector to reclaim unused resource.  However, on a busy site, it is likely that the connection pool will run out of connections before garbage collection kicks in.

2) You can raise the connection pool size in the connection string.  For example, you can add "Max Pool Size=100" to your connection string to increase the pool size to 100.