Singleton Data Access Object (Dao) & SQL Helper Instance, Is here any Performance drawback? - data-access-layer

Question

I need comments from Experts. I write my own SQL Helper Class to Communicate with DB.
Why I use it as because I try to
Encapsulate the Ado.Net logic.
Try to set a common standard for my developer in terms of DAL coding.
Flexible & Easy to use.
Same kind of code block for SQL Server/ Oracle / Access / Excel / Generic Database code block approach (SQL Server & Oracle) e.t.c.
Plug & Play or Reusable approach.
In terms of code optimization
This helper class or Assembly is CLS Compliant.
It pass Successfully by FxCop / Static Code Analysis.
I give you the sample Code Block (DAO). Please check bellow
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
#region include SQL Helper Namespace
using DBManager;
#endregion
#region include SQL Helper Namespace
using DBManager;
#endregion
namespace ContentManagementSystem.DataAccessLayer
{
/// <summary>
///
/// </summary>
public sealed class DaoContentOwner : DataAccessBase
{
#region CONSTRUCTOR
/// <summary>
///
/// </summary>
private DaoContentOwner()
{
GetInstance = new DaoContentOwner();
}
#endregion
//############################################# M E T H O D S ##########################
#region Retrieve Content Owner
/// <summary>
/// Retrieve Content Owner
/// </summary>
/// <returns></returns>
public static DataTable RetrieveContentOwner()
{
DataTable dt = null;
try
{
using (DBQuery dq = new DBQuery("stpGetContentOwner"))
{
dt = dq.ResultSetAsDataTable();
return dt;
}
}
catch (Exception)
{
throw;
}
finally
{
if (dt != null)
{
dt.Dispose();
}
}
}
#endregion
//############################################# P R O P E R T Y ########################
#region READ ONLY PROPERTY
/// <summary>
/// GetInstance of DaoContentOwner Class
/// </summary>
public static DaoContentOwner GetInstance { get; private set; }
#endregion
}
}
Justification:
"DataAccessBase" It is a Abstract class. Implement IDisposable Interface.
"DBQuery" is SQL Helper for SQL Server Only. It is a Sealed class. It is takes T-SQL / SP according to needs. Open an close database connection. No need to handel any thing by developer.
Why I make DAO Singleton Class, Because my all the methods withing DAO is a static method. I order to memory optimization I make it Singleton. It is also a design Principal.
Note: Needs comments. Whether need to change in the design or some thing is wrong that need to correct.

Answer 1

Personally I would go with:
DALFileItem dalF = new DALFileItem(DSN);
List<FileItem> list = dalF.GetAll("");
Allows accessing multiple databases, without making DSN static member.
In multithreaded environment only one thread will have access to the static method.
More object oriented: you can add interfaces, base classes and generics easier that way.