ACC97: Manipulating Objects with DAO May Cause Database Bloat (172285)

SYMPTOMS

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.

This article assumes that you are familiar with Visual Basic for Applications and with creating Microsoft Access applications using the programming tools provided with Microsoft Access. For more information about Visual Basic for Applications, please refer to the "Building Applications with Microsoft Access 97" manual.

RESOLUTION

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:

   Sub CreateTables()
      Dim db As Database
      Dim sql As String
      Dim i As Integer, j As Integer

      Set db = CurrentDb()
      For i = 1 To 20
         sql = "CREATE TABLE Table" & i & " ("
         For j = 1 To 200
            sql = sql & "Field" & j & " TEXT,"
         Next
         sql = Left$(sql, Len(sql) - 1) & ");"
         db.Execute sql
      Next
      Application.RefreshDatabaseWindow

   End Sub

MORE INFORMATION

This behavior typically occurs when using 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

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

?FileLen(CurrentDb.Name)

This function returns the file size in bytes of the currently opened database (Northwind.mdb). The file size of an unmodified copy of Northwind.mdb is approximately 1,546,240 bytes.
Create a module and type the following line in the Declarations section if it is not already there:
```
        Option Explicit
						
```

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

On the Debug menu, click Compile And Save All Modules. When Microsoft Access prompts you for the name of the module, click OK to accept the default name.
To run this procedure, type the following line in the Debug 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.
Type the following line in the Debug 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.
Press F11 to view the Database window.
On the Tools menu, point to Database Utilities, and then click Compact Database.
Press CTRL+G to open the Debug window.
Type the following in the Debug window, and then press ENTER:

?FileLen(CurrentDb.Name)

Note that the file size of Northwind.mdb after compacting is reported to be 1,898,496 bytes.