Cannot open any more tables - OleDbException was unhandled

Question

Good Day,
My question is how to handle the exception or get rid of the error pertaining to "Cannot open any more tables". For an overview to the program I was creating, I pull out the record of subject in ms access 2007, I loop to that record to randomly assign a schedule and one by one I insert the newly record with assigned schedule in the table.

My program flow of inserting the record work only for a certain number of times, like almost 200 and at some point it stop and pop-up the oledbexception

Thanks in advance for your time on answering my question.

here is my code for more detailed overview of my program,

Private Sub Assignsched(ByVal rType As String, ByVal subjectCode As String, ByVal SecID As String, ByVal CourseCode As String)
    If shrdcon.con.State = ConnectionState.Closed Then
        shrdcon.con.Open()
    End If
    Dim RoomNum As Integer
    dtARoom.Clear()
    Dim stoploop As Boolean

    Dim count As Integer = 0

    Dim rm1 As String
    RoomAssign = ""
    rm1 = "SELECT * FROM tblRoom WHERE RoomType = '" & rType & "'"
    Dim dat As New OleDbDataAdapter(rm1, shrdcon.con)
    dat.Fill(ds, "ARoom")




        stoploop = False
        count = 0
        Do Until stoploop = "True"
        RoomNum = rndm.Next(0, ds.Tables("ARoom").Rows.Count)
        RoomAssign = ds.Tables("ARoom").Rows(RoomNum).Item(1)

            ScheduleGeneration()

        If checkExisting(sTime, eTime, RoomAssign, daypick) = False Then


            RoomA = RoomAssign

            GenerateOfferingID()
            Dim cmd1 As New OleDbCommand()
            cmd1.CommandText = "INSERT INTO [tblSubjectOffer]([SubjectOID],[SubjectCode],[SectionID],[Day],[sTime],[eTime],[RoomName],[CourseCode]) VALUES('" & _
                                myId & "','" & subjectCode & "','" & SecID & "','" & daypick & "'," & sTime & "," & eTime & ",'" & RoomA & "','" & CourseCode & "')"
            cmd1.Connection = shrdcon.con
            cmd1.ExecuteNonQuery()
            cmd1.Dispose()

            Dim pipz As New OleDbCommand("Update tblGenerator Set NextNo='" & myId & "' where TableName ='" & "tblSubjectOffer" & "'", shrdcon.con)
            pipz.ExecuteNonQuery()
            pipz.Dispose()
            stoploop = True
        Else
            stoploop = False
        End If
            If stoploop = False Then

            If count = 30 Then
                stoploop = True
            Else

                count = count + 1

            End If
            End If
        Loop
End Sub

Answer 1

This is typical error happens with Microsoft Jet engine when You have exceeded the maximum number of open TableIDs allowed by the Microsoft Jet database engine, which is 2048 with Jet3.5 engine and 1024 with older engines.

Even though you are closing the Command objects after each use, you are still using the same connection for the whole process, which actually holds the TableID's and is at some point of time exceeding the number of allowed open TableID's.

A probable solution would be to update the Jet Engine with the latest, which is available here

It might solve your problem, but if you are already using the latest engine, you have to look into other options to reduce the number of DB operations.

Try using the UpdateBatch method for applying the updates as a batch.

Hope this helps

Private Sub Command1_Click()

    Dim myConnection As ADODB.Connection
    Dim rsData As ADODB.Recordset

    Set myConnection = New ADODB.Connection
    myConnection.ConnectionString = "xxxxxxxxxxxxxxxxxxxx"
    myConnection.Open

    Set rsData = New ADODB.Recordset
    rsData.CursorLocation = adUseClient
    rsData.Open "select * from mytable", myConnection, adOpenStatic, adLockBatchOptimistic

    For i = 1 To 10000
        rsData.AddNew
        rsData.Fields(0).Value = 1
        rsData.Fields(1).Value = 2
    Next i

    rsData.UpdateBatch

    rsData.Close
    myConnection.Close
    Set rsData = Nothing
End Sub

Answer 2

Good Evening, Recently I encounter this type of error and i was able to resolve it by adding con.close and call conState (a procedure conState- check below) before any insert/update or select statement In my code i have something like

For i = 0 To DataGridView1.RowCount - 1


            reg = DataGridView1.Rows(i).Cells(0).Value
            Label2.Text = reg

'i added this two lines
            ***con.Close()***
            ***Call conState()***

            Dim cmdcheck As New OleDbCommand("Select * from [2015/2016 UG CRF] where regno ='" & reg & "'", con)
            Dim drcheck As OleDbDataReader
            drcheck = cmdcheck.ExecuteReader
            If drcheck.Read = True Then

                GoTo A

            End If

            coursesFirst = String.Empty
            coursesSecond = String.Empty
            creditFirst = 0
            creditSecond = 0
            Dim cmdlevel As New OleDbCommand("Select * from [2015/2016 UG registration Biodata 5 april 16] where regno ='" & reg & "'", con)
            Dim drlevel As OleDbDataReader
            drlevel = cmdlevel.ExecuteReader

            If drlevel.Read = True Then
                level = drlevel.Item("level").ToString
                faculty = drlevel.Item("faculty").ToString
                program = drlevel.Item("programme").ToString

            End If

...............

next

The conState is a connection testing if connection is closed is should open it again like in below

Public Sub conState()
        If con.State = ConnectionState.Closed Then
            con.Open()

        End If

    End Sub

This stop the error message

Answer 3

I got this exception in my C# application and the cause was using OleDbDataReader instances without closing them:

OleDbDataReader reader = cmd.ExecuteReader();
bool result = reader.Read();
reader.Close(); // <= Problem went away after adding this
return result;