BUG: Repeatedly Opening and Closing DAO Recordset Increases Connections on SQL Server

• Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0

SYMPTOMS

The number of connections opened on SQL Server increases indefinitely if a Microsoft Data Access Objects (DAO) recordset is opened and closed repeatedly when you use DAO version 3.6. This does not happen if you use DAO version 3.51. You may see this behavior if you use sqlpassthrough in which the connection string is specified in the OpenDatabase statement.

RESOLUTION

Use a Querydef to create the connection instead of creating the connection in the OpenDatabase statement.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

Steps to Reproduce Behavior

1. Open a new Standard EXE project in Visual Basic. Form1 is created by default.



2. From the Project menu, choose References and then select Microsoft DAO 3.6 Data Objects.



3. Place two command buttons, named Command1 and Command2, on the form, and then paste the following code in form code window:




Dim db As Database
Dim rs As Recordset
Dim qd As QueryDef

Private Sub Command1_Click()

'-- Insert your own connect string here.
    Set db = OpenDatabase("", dbDriverNoPrompt, False, _
          "ODBC;DSN=sql7;UID=sa;PWD=;DATABASE=pubs;")
    Dim i As integer
    For i = 1 To 5
    '  reptq1 exists in the pubs database
        Set rs = db.OpenRecordset("reptq1", _
             dbOpenSnapshot, dbSQLPassThrough)
        rs.Close
    Next i
    
End Sub

Private Sub command2_Click()

   'Change the following string to match your path to the .mdb.
   Set db = OpenDatabase("d:\vbtest\db1.mdb")
   on error resume next
   db.QueryDefs.Delete "mysql7"
   on error goto 0
   Set qd = db.CreateQueryDef("mysql7")
   '-- Insert your own connect string below.
   With qd
     .Connect = "odbc;database=pubs;uid=sa;pwd=;dsn=sql7"
     .SQL = "select * from authors"
     .ReturnsRecords = True
   End With
   Dim i As Integer
   For i = 1 To 20
     Set rs = qd.OpenRecordset(dbOpenDynaset)
     rs.Close
   Next i
End Sub
 

4. Open ISQL/W in SQL Server 6.5 or Query Analyzer in SQL Server 7.0 and run the sp_who stored procedure. Note the number of connections.



5. Run the form created in step 1 and click Command1. Note the number of connections by executing sp_who again. Repeat this process a few times and note that the number of connections continues to increase. If you get a connection failure you have probably reached your connection limit.



6. Next, click Command2 repeatedly and note the number of connections returned by sp_who.

REFERENCES

For more information on SQLPassThrough Queries, see the following:

Haught, Dan; Jim Ferguson. Microsoft Jet Database Engine Programmer's Guide, Microsoft Press, Second Edition, 1997, pages 397-401.

(c) Microsoft Corporation 1999, All Rights Reserved. Contributions by Margery Simms, Microsoft Corporation.

Additional query words: jet Access 2000

Keywords : kbDatabase kbSQLServ kbGrpVBDB kbDSupport kbDAO360bug
Version : WINDOWS:5.0,6.0
Platform : WINDOWS
Issue type : kbbug