public void TestConnectionPool()
{
    // 최소 20 Connection 지정
    string strConn = "Data Source=(local);Initial Catalog=pubs;User id=test;Password=1;Min Pool Size=20;";    

    using (SqlConnection conn = new SqlConnection(strConn))
    {
        conn.Open();
        var cmd = new SqlCommand("select * from authors", conn);
        SqlDataReader rdr = cmd.ExecuteReader();
        rdr.Close();
    }

    // ClearAllPools 호출 이전
    // 결과 : 20 커넥션
    ShowPerfCounter();
    Console.WriteLine("Press Enter.");
    Console.ReadLine();

    // ClearAllPools 호출 이후
    // 결과 : 0 커넥션
    SqlConnection.ClearAllPools();
    Console.WriteLine("After ClearAllPools");
    ShowPerfCounter();
}

private void ShowPerfCounter()
{
    string processName = Assembly.GetExecutingAssembly().GetName().Name;
    int pid = Process.GetProcessesByName(processName)[0].Id;
    string instanceName = string.Format("{0}[{1}]", processName, pid);

    // .NET Data Provider for SqlServer 카테고리 안의
    // NumberOfPooledConnections 카운터 측정
    var counter1 = new PerformanceCounter(".NET Data Provider for SqlServer", "NumberOfPooledConnections", instanceName);            
    var v1 = counter1.NextValue();            
    Console.WriteLine(v1);                                
}