PRB: Memory Leak When MDAC Is Running on Windows NT 4.0

When you use the ODBC Driver for SQL Server with MDAC 2.6 or later under Windows NT 4.0, you may notice a memory leak.

This problem occurs because Dbnetlib.dll does not stay in memory.

There are two ways to work around this problem:

• Use the OLE DB provider for SQL Server.
• Make the following code changes:
  1. Add the following application programming interface (API) declaration to a module in your project:

     Public Declare Function LoadLibrary Lib "kernel32" & _
        Alias "LoadLibraryA" (ByVal lpLibFileName As String) As Long
     						

  2. Add the following code, which forces Dbnetlib.dll to stay in memory:

     Dim handle As Long
     Dim DLLName As String
     
     ' DBNETLIB.DLL should be located in the NT System directory.
     
     DLLName = "C:\WINNT\System32\DBNETLIB.DLL"
     handle = LoadLibrary(DLLName)
     						

Steps to Reproduce Behavior

1. Create a system DSN named SQLTest that points to your SQL Server.
2. Create a new Standard EXE project in Visual Basic. Form1 is created by default.
3. Add the following code to Form1:

   Private Sub Form_Load()
   
   Dim m_oConn As ADODB.Connection
   Dim counter As Long
   
   
   'Dim handle As Long
   'Dim DLLName As String
   
   ' DBNETLIB.DLL should be located in the NT System directory.
   
   'DLLName = "C:\WINNT\System32\DBNETLIB.DLL"
   'handle = LoadLibrary(DLLName)
   
   While (1)
       counter = counter + 1
       
       Set m_oConn = New ADODB.Connection
       m_oConn.Open "DSN=SQLTest"
       
       m_oConn.Close
       Set m_oConn = Nothing
       DoEvents
   Wend
   
   End Sub
   					

4. In Perfmon, add a counter that contains the following settings:
   Performance object: Process
   Select Counters from list: Private bytes
   Select Instances from list: VB6
   
5. Run the application, and observe the Perfmon counter.