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Microsoft KB Archive/170536

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Knowledge Base


Article ID: 170536

Article Last Modified on 7/13/2004



APPLIES TO

  • Microsoft Visual Basic 5.0 Professional Edition
  • Microsoft Visual Basic 6.0 Professional Edition
  • Microsoft Visual Basic 5.0 Enterprise Edition
  • Microsoft Visual Basic 6.0 Enterprise Edition



This article was previously published under Q170536

SUMMARY

In DAO, using the Close method on a database opened with ODBC drivers does not close the database; a cached connection remains idle before timing out. The default duration of this timeout is 600 seconds (10 minutes). If your application cannot accept the default behavior, you could control this time-out period by customizing the ConnectionTimeout value in Windows registry setting.

MORE INFORMATION

You can control the duration of ConnectionTimeout by creating a ConnectionTimeout registry entry for Jet. In Windows NT 3.51, the type is called "REG_DWORD"; in Windows 95, Windows 98, Windows Me (with DAO JET 3.6), Windows 2000, and Windows NT 4.0, the type is called "DWORD." "REG_DWORD" and "DWORD" are different terms referring to the same thing, a 32-bit number.

Although Visual Basic includes the SaveSetting and GetSetting functions to save and retrieve information from the registry, entries of types other than "REG_SZ" ("String" for Windows 95, Windows 98, Windows 2000, and Windows NT4.0) are not recognized. This article demonstrates how to use the registry API to set the DAO ConnectionTimeout setting to 1, which closes the connection after the Close method with only a one-second delay.

Sample Program

The following example has three CommandButton controls:

  • Command1 creates a testing Registry entry "Software\MyApp\Jet\3.5\Engines\ODBC" under HKEY_LOCAL_MACHINE root key, and sets the ConnectionTimeOut value to 1.
  • Command2 establishes the connection by opening the Pubs database.
  • Command3 closes the database.

You can check the detailed connection information by executing SP_WHO stored procedure on the SQL Server, then open/close database with/without the registry entry created.

  1. Start a new project in Visual Basic and choose "Standard EXE." Form1 is created by default.
  2. Reference the Microsoft DAO 3.5 Object Library under Project, References menu items.
  3. Add three CommandButtons, Command1, Command2, and Command3 to Form1.
  4. Paste the following code into the General Declarations section of Form1:

        Option Explicit
        Dim ws As Workspace
        Dim db As Database
        Dim TimeOutValue As Integer
    
        Private Sub CreateNewKey(sNewKeyName As String, lPredefinedKey As Long)
           Dim hNewKey As Long         'handle to the new key
           Dim lRetVal As Long         'result of the RegCreateKeyEx function
    
             lRetVal = RegCreateKeyEx(lPredefinedKey, sNewKeyName, 0&, _
                   vbNullString, REG_OPTION_NON_VOLATILE, KEY_ALL_ACCESS, _
                   0&, hNewKey, lRetVal)
             RegCloseKey (hNewKey)
        End Sub
    
        Private Sub SetKeyValue(sKeyName As String, sValueName As String, _
             vValueSetting As Variant)
        Dim lRetVal As Long         'result of the SetValueExLong function
             Dim hKey As Long            'handle of open key
    
             lRetVal = RegOpenKeyEx(HKEY_LOCAL_MACHINE, sKeyName, 0, _
                                KEY_ALL_ACCESS, hKey)
             lRetVal = RegSetValueExLong(hKey, sValueName, 0&, _
                                REG_DWORD, vValueSetting, 4)
             RegCloseKey (hKey)
        End Sub
    
        Private Function QueryValue(sKeyName As String, sValueName As String) _
                                    As Integer
             Dim lRetVal As Long        'result of the API functions
             Dim hKey As Long           'handle of opened key
             Dim vValue As Variant      'setting of queried value
    
             lRetVal = RegOpenKeyEx(HKEY_LOCAL_MACHINE, sKeyName, 0, _
                                    KEY_ALL_ACCESS, hKey)
             lRetVal = QueryValueEx(hKey, sValueName, vValue)
             If lRetVal = ERROR_NONE Then
                 QueryValue = True
                 TimeOutValue = vValue
             Else
                 QueryValue = False
             End If
             RegCloseKey (hKey)
        End Function
    
        Private Sub Command1_Click()
             If QueryValue("Software\MyApp\Jet\3.5\Engines\ODBC", _
                    "ConnectionTimeout") Then
                If TimeOutValue <> 1 Then
                 SetKeyValue "Software\MyApp\Jet\3.5\Engines\ODBC", _
                    "ConnectionTimeout", 1
                End If
              MsgBox "Test registry key already set"
             Else
                 CreateNewKey "Software\MyApp\Jet\3.5\Engines\ODBC", _
                              HKEY_LOCAL_MACHINE
                SetKeyValue "Software\MyApp\Jet\3.5\Engines\ODBC", _
                            "ConnectionTimeout", 1
                MsgBox "Test registry key created successfully"
             End If
        End Sub
    
        Private Sub Command2_Click()
             Dim strConnect As String
    
             DBEngine.IniPath = "HKEY_LOCAL_MACHINE\Software\MyApp\Jet\3.5"
             Set ws = DBEngine.Workspaces(0)
             strConnect = "ODBC;SERVER=MyServer;" & _
                   "DRIVER={SQL  SERVER};DATABASE=pubs;UID=sa;PWD=;"
             Set db = ws.OpenDatabase("", False, False, strConnect)
             MsgBox "Connection established"
        End Sub
    
        Private Sub Command3_Click()
             If db Is Nothing Then
                MsgBox "Already Disconnected"
                Exit Sub
             End If
    
             db.Close
             ws.Close
    
             Dim Start As Long
             Start = Timer
             Do
               DBEngine.Idle dbFreeLocks
             DoEvents
             Loop While Timer <= Start + 1
             MsgBox "Disconnected"
        End Sub
    
        Private Sub Form_Load()
             Command1.Caption = "Create/Set test registry entry"
             Command2.Caption = "Open database"
             Command3.Caption = "Close database"
        End Sub
    
                        
  5. From the Project menu, select Add Module, then click Module. Copy and paste the following code into the General Declarations section of Module1:

        Option Explicit
    
        Global Const REG_DWORD As Long = 4
        Global Const HKEY_LOCAL_MACHINE = &H80000002
        Global Const ERROR_NONE = 0
        Global Const KEY_ALL_ACCESS = &H3F
        Global Const REG_OPTION_NON_VOLATILE = 0
        Global TimeOut As Integer
    
        Declare Function RegCloseKey Lib "advapi32.dll" _
                           (ByVal hKey As Long) As Long
        Declare Function RegCreateKeyEx Lib "advapi32.dll" Alias _
          "RegCreateKeyExA" (ByVal hKey As Long, ByVal lpSubKey As String, _
          ByVal Reserved As Long, ByVal lpClass As String, ByVal dwOptions _
          As Long, ByVal samDesired As Long, ByVal lpSecurityAttributes _
          As Long, phkResult As Long, lpdwDisposition As Long) As Long
        Declare Function RegOpenKeyEx Lib "advapi32.dll" Alias _
          "RegOpenKeyExA" (ByVal hKey As Long, ByVal lpSubKey As String, _
          ByVal ulOptions As Long, ByVal samDesired As Long, phkResult As _
          Long) As Long
        Declare Function RegQueryValueExLong Lib "advapi32.dll" Alias _
          "RegQueryValueExA" (ByVal hKey As Long, ByVal lpValueName As _
          String, ByVal lpReserved As Long, lpType As Long, lpData As _
          Long, lpcbData As Long) As Long
        Declare Function RegQueryValueExNULL Lib "advapi32.dll" Alias _
          "RegQueryValueExA" (ByVal hKey As Long, ByVal lpValueName As _
          String, ByVal lpReserved As Long, lpType As Long, ByVal lpData _
          As Long, lpcbData As Long) As Long
    
        Declare Function RegSetValueExLong Lib "advapi32.dll" Alias _
          "RegSetValueExA" (ByVal hKey As Long, ByVal lpValueName As String, _
          ByVal Reserved As Long, ByVal dwType As Long, lpValue As Long, _
          ByVal cbData As Long) As Long
    
        Function QueryValueEx(ByVal lhKey As Long, ByVal szValueName As _
                 String, vValue As Variant) As Long
          Dim cch As Long
          Dim lrc As Long
          Dim lType As Long
          Dim lValue As Long
          Dim sValue As String
    
          On Error GoTo QueryValueExError
    
          lrc = RegQueryValueExNULL(lhKey, szValueName, 0&, lType, 0&, cch)
          If lrc <> ERROR_NONE Then Error 5
    
          lrc = RegQueryValueExLong(lhKey, szValueName, 0&, lType, _
                lValue, cch)
          If lrc = ERROR_NONE Then vValue = lValue
    
        QueryValueExExit:
          QueryValueEx = lrc
          Exit Function
        QueryValueExError:
          Resume QueryValueExExit
        End Function
    
                        
  6. Make sure to change your SERVER, UID, and PWD parameters in the connection string under Command2_Click.
  7. Start the program or press the F5 key.
  8. You can observe the connection information by executing the SP_WHO stored procedure at SQL Server. Compare the result before and after opening a database and before and after closing the database.

NOTE: Modify the Jet Engine version in the code, from 3.5 to a higher number, in order to work with the required version of the Jet Engine.


REFERENCES

For additional information, please see the following articles in the Microsoft Knowledge Base:

145679 How To Use the Registry API to Save and Retrieve Setting


110227 PRB: ODBC Database Remains Open After a Close Method Used


Keywords: kbhowto kbmdacnosweep KB170536