Microsoft KB Archive/250315

Knowledge Base

FIX: Memory Leak When You Clone a Server-Side Recordset

Article ID: 250315

Article Last Modified on 5/17/2007

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APPLIES TO

• Microsoft ActiveX Data Objects 2.5

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This article was previously published under Q250315

SYMPTOMS

If you clone a server-side ADO Recordset object, you may encounter a memory leak. This behavior can occur in varying degrees in any of the following products:

• Microsoft OLE DB Provider for ODBC
• Microsoft OLE DB Provider for Jet, version 4.0
• Microsoft OLE DB Provider for SQL Server

RESOLUTION

If it is necessary to clone a Recordset, use a client-side cursor.

STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are listed at the beginning of this article. This bug was corrected in ActiveX Data Objects (ADO), version 2.6. You can download the latest version of ADO from the following Microsoft Web site:

http://msdn2.microsoft.com/en-us/data/aa937695.aspx

MORE INFORMATION

Steps to Reproduce Behavior

1. Create a new Standard EXE project in Visual Basic. Form1 is created by default.
2. From the Project Menu, click References, and select the Microsoft Active X Data Object 2.5 check box.

3. Paste the following code in the form module of Form1:
   
   Note You must change User ID=<User ID> to the correct value before you run this code. Make sure that User ID has the appropriate permissions to perform this operation on the database.

   Option Explicit
   
   Private Sub Form_Load()
       Dim cnn As ADODB.Connection
       Dim rs As ADODB.Recordset
       Dim crs As Object
       
       Set cnn = CreateObject("ADODB.Connection")
       cnn.Open "Provider=SQLOLEDB;Data Source=servername;" & _
       "Initial Catalog=pubs;User ID=<User ID>;"
       
       Set rs = New ADODB.Recordset
       rs.CursorLocation = adUseServer
       'rs.CursorLocation = adUseClient
       rs.Open "select * from authors where au_lname like 'S%'", _
           cnn, adOpenStatic, adLockReadOnly
       Dim i As Long
       For i = 0 To 120000
           Set crs = rs.Clone
           crs.Filter = "Au_Lname = 'Smith'"
           crs.Close
           Set crs = Nothing
       Next i
       rs.Close
       cnn.Close
       Set rs = Nothing
       Set cnn = Nothing
   End Sub
                       

4. Modify the connection string to connect to your Microsoft SQL Server database.
5. Start Performance Monitor, and monitor the private bytes for the Visual Basic 6.0 process.
6. Run the code, and notice that the private bytes increase steadily. When the private bytes reach 100 percent, most likely the application locks up.

7. Uncomment the following line of code:

   'rs.CursorLocation = adUseClient

   and comment the following line:

   rs.CursorLocation = adUseServer

8. Run the application, and monitor the private bytes. Notice that the private bytes increase but then level off, and the application does not lock up.

Additional query words: mem leak serverside cursor

Keywords: kbado260fix kbbug kbfix KB250315

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