VB3 Speed Up Data Access by Using BeginTrans & CommitTrans (109830)

MORE INFORMATION

You can tune the performance of Visual Basic by using transactions for operations that update data. A transaction is a series of operations that must execute as a whole or not at all. You mark the beginning of a transaction with the BeginTrans statement. You use the Rollback or CommitTrans statement to end a transaction.

You can usually increase the record updates per second (throughput) of an application by placing operations that update data within an Access Basic transaction.

Because Visual Basic locks data pages used in a transaction until the transaction ends, using transactions will prevent access to those data pages by other users while the transaction is pending. If you use transactions in a multi-user environment, try to find a balance between data throughput and data access.

If database operations are not within a transaction, every Update method causes a disk write.

Transactions are very fast because they are written to a buffer in memory instead of to disk. CommitTrans writes the changes in the transaction buffer to disk.



Robust error trapping is important when using transactions to avoid losing writes if the program gets an error in the middle of a transaction.

For more performance tuning tips for data access in Microsoft Visual Basic version 3.0, see the PERFORM.TXT file.

Step-by-Step Example

1. Start a new project in Visual Basic. Form1 is created by default.
2. Add the following to the Form Load event code:
   

      Sub Form_Load ()
         Dim Starttime, Endtime
         Dim db As Database
         Dim t As Table
         Dim i As Integer
         Dim tempName As String
         Dim temphone As String
         Set db = OpenDatabase("c:\BIBLIO.MDB")  ' Uses a copy of BIBLIO.MDB
         Set t = db.OpenTable("Publishers")
         Starttime = Now
         'BeginTrans   ' Add this and CommitTrans (below) for greater speed.
         For i = 1 To 100
            tempName = "testname" & Str$(i)  'Make an arbitrary unique string.
            tempPhone = Str$(i)              'Make arbitrary number.
            t.AddNew  'AddNew clears copy buffer to prepare for new record.
            t!PubID = 30 + i  ' Set primary key to unique value.
            t!Name = tempName  ' Set Name field to unique value.
            t!Telephone = tempPhone  ' Set Telephone field to unique value.
            t.Update   ' Write the record to disk or to transaction buffer.
         Next i
         'CommitTrans   ' Add this and BeginTrans (above) for greater speed.
         Endtime = Now
         MsgBox "Time required= " & Format(Endtime - Starttime, "hh:mm:ss")
         t.Close
         db.Close
         End
      End Sub
   

   The above code adds 100 new records to the BIBLIO.MDB database file. Add the records to a copy of BIBLIO.MDB instead of to the original.
3. Start the program (or press the F5 key). A message box reports the time required to add 100 new records. Close the form to end the program.

If you don't use the BeginTrans and CommitTrans statements, this program reports 17 seconds to add 100 records on a 486/66 PC. When you add BeginTrans and CommitTrans as shown in the program comments above, the program takes less than 1 second on that computer. Performance may vary on different computers.