Significantly Improve the Performance of Microsoft Access Databases with Linked Tables

Provided by: Luke Chung, FMS President

A Split Microsoft Access Database Architecture Offers Many Advantages

A split database architecture is best for developing, maintaining, and deploying Microsoft Access applications. The front-end database contains all the Access objects except the tables which reside in a separate back-end Access Jet database. The front-end database links to the tables in the back-end database, so it can be updated without worrying about changes to the data.

This is particularly important for multi-user applications where each user has a copy of the front-end database on their machine sharing the same centralized data. When the application is enhanced (new queries, forms, reports, code, etc.), it is simply distributed to each user. Programs like our Total Access Startup can centralize and automate the distribution process.

If you are not familiar with a split database architecture, read our paper on Splitting Microsoft Access Databases to Improve Performance and Simplify Maintainability

Microsoft Access Database with Linked Tables Sometimes Perform Poorly

When a single database is converted to a split-database design, one sometimes sees significant performance degradation, especially over a network. Speed may vary with different portions of the application and number of users. Some people settle for this but there may be a simple way to significantly improve performance.

Microsoft Access Lock Files

When a database is opened, Microsoft Access creates a lock file on disk. You may see these are *.LDB or *.LACCDB files. When the database is closed, the lock file is deleted.

This is not a big deal for a single MS Access database application which would create the lock file when the database is opened and maintain it until the database is closed. But in a linked database design, the lock file on the back-end database may be created and deleted every time a table is opened and closed. When no connections to any tables on the back end database remain open, the lock file is deleted. That takes time.

Always Keep a Connection Open to the Back End Database While Your Application Runs

You can significantly improve the performance of your Access database by maintaining an open connection to the back-end database throughout the time your front-end database is opened.

By forcing Access to keep the linked table's database open, Access avoids creating a new lock on the backend database every time one of its tables is used. This lets you open tables, forms, and reports much faster. Over a network, you'll usually see a substantial improvement with how quickly a form opens when it's based on a linked table.

The DAO OpenDatabase Method

To create a persistent connection to the linked database, open a MS Access database variable in VBA using the DAO OpenDatabase method. Keep this variable open as long as your application is running.

The procedure below supports multiple backend databases. Edit the section with the list of databases to open, then call this when your application starts:

OpenAllDatabases True

When you finish, call this to close the database variables/handles:

OpenAllDatabases False

Here's the procedure code:

Sub OpenAllDatabases(pfInit As Boolean)
  ' Open a handle to all databases and keep it open during the entire time the application runs.
  ' Params  : pfInit   TRUE to initialize (call when application starts)
  '                    FALSE to close (call when application ends)
  ' Source  : Total Visual SourceBook

  Dim x As Integer
  Dim strName As String
  Dim strMsg As String
 
  ' Maximum number of back end databases to link
  Const cintMaxDatabases As Integer = 2

  ' List of databases kept in a static array so we can close them later
  Static dbsOpen() As DAO.Database
 
  If pfInit Then
    ReDim dbsOpen(1 To cintMaxDatabases)
    For x = 1 To cintMaxDatabases
      ' Specify your back end databases
      Select Case x
        Case 1:
          strName = "H:\folder\Backend1.mdb"
        Case 2:
          strName = "H:\folder\Backend2.mdb"
      End Select
      strMsg = ""

      On Error Resume Next
      Set dbsOpen(x) = OpenDatabase(strName)
      If Err.Number > 0 Then
        strMsg = "Trouble opening database: " & strName & vbCrLf & _
                 "Make sure the drive is available." & vbCrLf & _
                 "Error: " & Err.Description & " (" & Err.Number & ")"
      End If

      On Error GoTo 0
      If strMsg <> "" Then
        MsgBox strMsg
        Exit For
      End If
    Next x
  Else
    On Error Resume Next
    For x = 1 To cintMaxDatabases
      dbsOpen(x).Close
    Next x
  End If
End Sub

This simple technique yields considerable performance gains.

Additional Resources

• Microsoft Access Best Practices: Finding Errors, Suggestions, and Performance Tips in Your Databases with Total Access Analyzer
• Source code for Starting Microsoft Access databases in Total Visual SourceBook
• Module class for Managing Microsoft Access Linked Tables and Databases in Total Visual SourceBook
• Splitting Microsoft Access Databases to Improve Performance and Simplify Maintainability
• 100+ Microsoft Access Performance Tips to Speed up Your Access Databases
• More tips

Good luck!