ADO记录集在16个创建之后开始建立新连接

Question

这可能是我遇到过的一个bug最困惑的地方。

下面是一些会产生错误的VB代码。我不关心这个事实，我不必创建新的记录集，这是故意触发该错误的。

Public Module ConnectionSetup 

Public ActiveTDConnection As ADODB.Connection 

Public Sub ConnectToTD(ByVal userName As String, ByVal Password As String, ByVal dsn As String) 

    ActiveTDConnection = New ADODB.Connection 

    ActiveTDConnection.ConnectionString = "Provider=MSDASQL.1;Persist Security Info=True;" & _ 

       "User ID=" & userName & ";Password=" & Password & ";" & _ 

       "Data Source=" & dsn & ";Mode=Read;" & _ 

       "UID=" & userName & ";AUTHENTICATION=LDAP;Initial Catalog=(Default)" 

    ActiveTDConnection.CommandTimeout = 0 

    ActiveTDConnection.Open(ActiveTDConnection.ConnectionString) 

End Sub 

End Module 

Module Module1 

Sub Main() 

    ConnectionSetup.ConnectToTD("XXX", "XXX", "XXX") 


    Dim DB_qry As String 

    Dim sessionQry As String 

    Dim i As Integer = 1 

    Dim sessionRS As New ADODB.Recordset 


    DB_qry = "SELECT TOP 1 * FROM dbc.databases" 

    sessionQry = "SELECT COUNT(*) FROM dbc.SessionInfo WHERE userName = 'MyUserName'" 


    Do While i <= 18 

     Dim DB_rs As New ADODB.Recordset 

     DB_rs.Open(DB_qry, ActiveTDConnection) 

     sessionRS.Open(sessionQry, ActiveTDConnection) 

     ' This starts going up by 1 on each loop, after 16. 
     Debug.Print(sessionRS.Fields.Item(0).Value) 

     Do While Not DB_rs.EOF 

      MsgBox(i) 

      i += 1 

      DB_rs.MoveNext() 

     Loop 

     DB_rs.Close() 

     DB_rs = Nothing 

     sessionRS.Close() 

    Loop 

End Sub 

第16次迭代后，每个新打开的recordSet都会产生一个新的连接。所以我的代码随机开始冒着最大化会话限制的风险。

1.）为什么会发生这种情况？

2.）我该如何预防它？

Answer 1

Sub Main() 

    ConnectionSetup.ConnectToTD("XXX", "XXX", "XXX") 


    Dim DB_qry As String 
    Dim sessionQry As String 

    Dim i As Integer = 1 

    Dim sessionRS As New ADODB.Recordset 

    DB_qry = "SELECT SESSION" 

    sessionQry = "SELECT COUNT(*) FROM dbc.SessionInfo WHERE userName = 'MyUserName'" 


    Do While i <= 18 

     Dim DB_rs As New ADODB.Recordset 

     DB_rs.Open(DB_qry, ActiveTDConnection) 

     sessionRS.Open(sessionQry, ActiveTDConnection) 

     ' This starts going up by 1 on each loop, after 16. 
     'Debug.Print(sessionRS.Fields.Item(0).Value) 

     Do While Not DB_rs.EOF 

      MsgBox("Sessions: " & sessionRS.Fields.Item(0).Value & " Cnt: " & i & " SID: " & DB_rs.Fields.Item(0).Value) 

      i += 1 

      DB_rs.MoveNext() 

     Loop 

     DB_rs.Close() 
     DB_rs = Nothing 
     sessionRS.Close() 

    Loop 

End Sub