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Why is this loop slowing down as number of records are processed?

spoowiz
spoowiz asked
on
Medium Priority
214 Views
Last Modified: 2010-05-01
This following code took 13 minutes!
The Label1 counter was fast in the beginning but as the loop progessed it slowed down to a crawl.
Why would this happen and how can i correct it?

lstgVC is a mySQL local database
lstgSrc is msAccess database

thanks
phil

    Do Until lstgVC.EOF
        inCnt = inCnt + 1
        Label1.Caption = inCnt & " of " & recCnt
        Label1.Refresh
        DoEvents
            lstgSrc.Open "SELECT id FROM Table1" _
                         & "WHERE id=" & lstgVC!ID, _
                         cnSrc, adOpenKeyset, adLockOptimistic
        If lstgSrc.RecordCount = 0 Then
            lstgVC!Status = "U"
            lstgVC!DeleteFlag = 1
            'lstgVC.Update
            lstgVC.CancelUpdate   <---------------------note that I'm not even doing an update
            outCnt = outCnt + 1
            txtStatus.Text = txtStatus.Text & vbCrLf & str
            txtStatus.Refresh
        End If
        lstgSrc.Close
        Set lstgSrc = Nothing
        lstgVC.MoveNext
    Loop
Comment
Watch Question

because of this line:

txtStatus.Text = txtStatus.Text & vbCrLf & str


Remove it and try again
If no such slowing occurs, replace it with :

txtStatus.SelStart=Len(txtStatus.Text)
txtStatus.SelText=vbCrLf & str

Author

Commented:
hi,
that's not it. i even commented it out and still slows down.
btw, lstgVC selection count is only 2900 records. By about 900 records into it starts slowing down. by 1200 records into it, it REALLY slow, maybe 3 to 5 records per second.
phil
Ok , comment everythink between Do...Loop and keep only:

lstgSrc.Open "SELECT id FROM Table1" _
                         & "WHERE id=" & lstgVC!ID, _
                         cnSrc, adOpenKeyset, adLockOptimistic



Is problem occurs again ?

Author

Commented:
Good idea.
I took out basically everything but lstgSrc.open/close and it behaves the same.
I then took out the lstgSrc.open/close and takes no time to finish 2800 records.
So it must be the lstgSrc.Open stmt causing it.
I wonder why.

Author

Commented:
Another thing... the msAccess database table I'm opening (lstgSrc) is a linked table from msAccess to a .dbf (dbase) file.

Commented:
do you have an index on the ID column of your Access table?  

Author

Commented:
yes. the dbase file has an index on the ID field and opening it in design mode from msAccess shows that it it is indexed.
Try change this:
lstgSrc.Open "SELECT id FROM Table1" _
                         & "WHERE id=" & lstgVC!ID, _
                         cnSrc, adOpenKeyset, adLockOptimistic

With this:
Dim rstRecordset As Recordset
.....
.....
Set rstRecordset=cnSrc.Execute("SELECT id FROM Table1 WHERE id=" & lstgVC!ID)

Keep other lines commented. Again same problem ?

Author

Commented:
same.
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Author

Commented:
I re-wrote by inserting all the ID's from the dbase file to another msAccess TEMP table I just created and ran it. It finished in 13 seconds. Many repetetive calls to the dbase file seems to be the problem. Well, hopefully I need to do this in another place. The workaround is to use the temp file. Thanks.
Good luck !
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