ACC2000: Manipulating Objects with ADO May Cause Database Bloat

When you use ActiveX Data Objects (ADO) to create objects in a database, the size of the database increases substantially during the operation. After compacting, the size of the database is much smaller.

Use SQL Data-Definition Language (DDL) statements rather than ADO to create or modify database objects. For example, you can use the following procedure to work around the behavior demonstrated in the "Steps to Reproduce Problem" section later in this article:

Microsoft provides programming examples for illustration only, without warranty either expressed or implied. This includes, but is not limited to, the implied warranties of merchantability or fitness for a particular purpose. This article assumes that you are familiar with the programming language that is being demonstrated and with the tools that are used to create and to debug procedures. Microsoft support engineers can help explain the functionality of a particular procedure, but they will not modify these examples to provide added functionality or construct procedures to meet your specific requirements.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

This behavior typically occurs when you use ADO to create or modify a large number of database objects. The following example demonstrates this by using ADO to create twenty tables, each with two hundred fields. In this example, reducing the number of fields created in the example greatly reduces the amount of database bloat.

NOTE: The sample code in this article uses Microsoft ActiveX Data Objects. For this code to run properly, you must reference the Microsoft ActiveX Data Objects 2.x Library (where 2.x is 2.1 or later.) To do so, click References on the Tools menu in the Visual Basic Editor, and make sure that the Microsoft ActiveX Data Objects 2.x Library check box is selected.

The sample code in this article uses ADO Extensions for DDL and Security. For this code to run properly, you need to reference the Microsoft ADO Ext. 2.1 for DDL and Security.

Steps to Reproduce Problem

1. Open the sample database Northwind.mdb.
2. On the Tools menu, point to Database Utilities, and then click Compact and Repair Database.
3. Press CTRL+G to open the Immediate window.
4. Type the following in the Immediate window, and then press ENTER:

   ?FileLen(CurrentDb.Name)
   						

   Note that this function returns the file size in bytes of the currently opened database (Northwind.mdb). Take note of the current size.
5. Create a module and type the following line in the Declarations section if it is not already there:

   Option Explicit
   					

6. Type the following procedure:

   Sub ADOX_CreateTables()
   
      Dim cat As New ADOX.Catalog
      Dim conn As New ADODB.Connection
      Dim tbl As New ADOX.Table
      Dim i As Integer, j As Integer
   
      Set conn = CurrentProject.Connection
      Set cat.ActiveConnection = conn
   
      For i = 1 To 20
   
         With tbl
            'Create a new table
            .Name = "tblTest" & i
   
            'Add 200 text fields
            For j = 1 To 200
               .Columns.Append "Field" & j, adVarWChar, 50
            Next j
         End With
   
         'Append the table into the Catalog's tables collection
         cat.Tables.Append tbl
         Set tbl = Nothing
   
      Next
      Application.RefreshDatabaseWindow
   
   End Sub
   					

7. On the File menu, click Save Northwind. When Microsoft Access prompts you to save the module, click Yes. In the Save As dialog box, click OK to accept the default name.
8. To run this procedure, type the following line in the Immediate window,and then press ENTER. It may take several minutes for this procedure to run.

   ADOX_CreateTables
   						

   Note that twenty tables are added to the database, each with two hundred fields.
9. Type the following line in the Immediate window, and then press ENTER:

   ?FileLen(CurrentDb.Name)
   						

   Note that the size of the Northwind.mdb file is now is significantly greater.
10. On the taskbar click Microsoft Access (or Northwind: Database) to get back to the Database window.
11. On the Tools menu, point to Database Utilities, and then click Compact and Repair Database.
12. Press CTRL+G to open the Immediate window.
13. Type the following in the Immediate window, and then press ENTER:

    ?FileLen(CurrentDb.Name)
    						

    Note that the size of the Northwind.mdb file after compacting is now closer to the size that you saw on step 4.

For more information about data-definition queries, click Microsoft Access Help on the Help menu, type work with tables or indexes by using an SQL data-definition query in the Office Assistant or the Answer Wizard, and then click Search to view the topic.