ACC2000: Manipulating Objects with DAO May Cause Database Bloat

When you use Data Access Objects (DAO) 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.

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.

Use SQL Data Definition Language (DDL) statements rather than DAO 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 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 DAO to create or modify a large number of database objects. The following example demonstrates this by using DAO 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.

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)
   						

   This function returns the file size in bytes of the currently opened database (Northwind.mdb). 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 CreateTables()
      Dim db As Database
      Dim t As TableDef
      Dim f As Field
      Dim i As Integer, j As Integer
   
      Set db = CurrentDb()
      For i = 1 To 20
         Set t = db.CreateTableDef("Table" & i)
         For j = 1 To 200
            Set f = t.CreateField("Field" & j)
            f.Type = dbText
            f.size = 50
            t.Fields.Append f
         Next
         db.TableDefs.Append t
      Next
      Application.RefreshDatabaseWindow
   End Sub
   					

7. On the Debug menu, click Compile Northwind. When Microsoft Access prompts you for the name of the module, 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.

   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 file size of Northwind.mdb is now reported to be more than 52 megabytes.
10. On the Task Bar click Microsoft Access 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 file size of Northwind.mdb after compacting is now back to the size you saw in step 4.

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