SQL Server connection remains open, even after closing - asp.net

Question

I have a website that is designed to multi-tiered. My code works, but I have noticed that the larger my app becomes, the more SQL database connections start to stack up and remain open. This eventually causes this error:
System.InvalidOperationException: 'Timeout expired. The timeout
period elapsed prior to obtaining a connection from the pool. This
may have occurred because all pooled connections were in use and max
pool size was reached.'
My code is split into 3 layers. They are:
Application layer. Every time it wants to CRUD, is calls the Business Layer.
Business Layer - does business logic. When it wants to interface with the MS SQL db, it connects via ConnectionAdapter layer.
The ConnectionAdapter inherits from a SqlConnectionAdapter class and does the actual db interactions.
The following is pseudo code for each:
Application
My application may call the business layer multiple times. Particularly when doing AJAX requests. An example would be like:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
Dim dp As New DataProxy
Dim listOfObs As New List(Of MyObject)
dim someId as integer = 1
Try
If Not Page.IsPostBack Then
listOfObs = dp.ExampleReadFuncion(someId)
End If
Catch ex As Exception
Throw
Finally
dp.dispose()
dp = Nothing
SetMenue()
End Try
End Sub
DatatProxy (business layer)
Public Class DataProxy
Dim scConAdapter As New ConnectionAdapter
Public Sub New()
Try
scConAdapter.Connect()
Catch ex As Exception
Throw
End Try
End Sub
Public Sub dispose()
scConAdapter.Dispose()
End Sub
Private Shared Sub Main()
End Sub
Public Function ExampleReadFuncion(ByVal someId As Integer) As List(Of MyObject)
Dim successFactor As LogStatusEnum = LogStatusEnum.INFO
Dim newEx As Exception = Nothing
Dim conn As New ConnectionAdapter
Dim myObj As ActivityMarker
Dim listOfObs As New List(Of MyObject)
Dim dr As SqlDataReader = Nothing
Try
successFactor = LogStatusEnum.INFO
conn.Connect()
dr = conn.ExampleReadFuncion(someId)
Using dr
If (dr.HasRows = True) Then
While dr.Read
myObj = New myObj
myObj.Marker_Id = dr.Item("id")
myObj.Acitvity_Id = dr.Item("someValue")
listOfObs.Add(myObj)
End While
End If
End Using
Return listOfObs
Catch ex As Exception
successFactor = LogStatusEnum.ERRORS
Throw
Finally
dr.Close()
dr = Nothing
conn.Dispose()
conn = Nothing
End Try
End Function
End class
ConnectionAdapter
Public Class ConnectionAdapter
Inherits SqlConnectionAdapter
Public Sub New()
End Sub
Public Function ExampleReadFuncion(ByVal someId As Integer) As SqlDataReader
Try
Dim dr As SqlDataReader = Nothing
Dim selectString As New StringBuilder
Dim cmd As SqlCommand = Nothing
Try
cmd = CreateCommand()
selectString.Append("SELECT * " & vbCrLf)
selectString.Append("FROM " & vbCrLf)
selectString.Append("dbo.mytable " & vbCrLf)
selectString.Append("WHERE " & vbCrLf)
selectString.Append("id = #SOME_ID " & vbCrLf)
With cmd
.CommandType = CommandType.Text
.CommandText = selectString.ToString
.Parameters.Add("#SOME_ID", SqlDbType.Int).Value = someId
dr = .ExecuteReader
End With
Catch ex As Exception
Throw
Finally
cmd.Dispose()
End Try
Return dr
Catch ex As Exception
Throw ex
End Try
End Function
end class
SqlConnectionAdapter
Public MustInherit Class SqlConnectionAdapter
Protected CurrentTransaction As SqlTransaction
Public Property db As SqlConnection
Public Property Password As String
Public Property TNSName As String
Public Property User As String
Public Property DBName As String
Public Property PortNumber As Integer
Public Overridable Sub Dispose()
Try
If Not CurrentTransaction Is Nothing Then
CurrentTransaction.Commit()
End If
Catch ex As Exception
Throw
Finally
If Not db Is Nothing Then
db.Close()
db.Dispose()
db = Nothing
End If
End Try
End Sub
Public Overridable Sub Connect()
Try
Dim appSettings = ConfigurationManager.AppSettings
If (appSettings("releaseVersion") = "DEBUG") Then
Connect(appSettings("db_sqlHost"), appSettings("db_sqlDb"))
Else
Connect(appSettings("db_sqlHost"), appSettings("db_sqlPort"), appSettings("db_sqlDb"), appSettings("db_sqlUser"), appSettings("db_sqlPassword"))
End If
Catch ex As Exception
Throw
End Try
End Sub
Public Sub Connect(ByVal GetServername As String, ByVal GetDatabaseName As String)
Try
TNSName = GetServername
DBName = GetDatabaseName
db = New SqlConnection
db = SqlConnectionUtilities.GetConnection(GetServername, GetDatabaseName)
Catch ex As Exception
Throw
End Try
End Sub
Public Sub Connect(ByVal GetServerName As String, ByVal GetPort As Long, ByVal GetDatabase As String, ByVal GetUsername As String, ByVal Getpassword As String)
Try
User = GetUsername
Password = Getpassword
PortNumber = GetPort
DBName = GetDatabase
TNSName = GetServerName
db = New SqlConnection
db = SqlConnectionUtilities.GetConnection(GetServerName, GetPort, GetDatabase, GetUsername, Getpassword)
Catch ex As Exception
Throw
End Try
End Sub
Protected Function CreateCommand() As SqlCommand
Dim ret As SqlCommand = Nothing
Try
ret = db.CreateCommand
If Not CurrentTransaction Is Nothing Then
ret.Transaction = CurrentTransaction
End If
Catch ex As Exception
Throw
Finally
End Try
Return ret
End Function
Public Sub BeginTransaction()
If CurrentTransaction Is Nothing Then
CurrentTransaction = db.BeginTransaction
End If
End Sub
Public Sub CommitTransaction()
If Not CurrentTransaction Is Nothing Then
CurrentTransaction.Commit()
CurrentTransaction.Dispose()
CurrentTransaction = Nothing
End If
End Sub
Public Sub RollbackTransaction()
If Not CurrentTransaction Is Nothing Then
CurrentTransaction.Rollback()
CurrentTransaction.Dispose()
CurrentTransaction = Nothing
End If
End Sub
Protected Overrides Sub Finalize()
MyBase.Finalize()
End Sub
End Class
Utilities class
Public Class SqlConnectionUtilities
Public Shared Property connectionString As String
Public Shared Function GetConnection(ByVal ServerName As String, ByVal Port As String, ByVal Database As String, ByVal username As String, ByVal password As String) As SqlConnection
Dim connString As New StringBuilder
Dim con As SqlConnection
Try
connString.Append("Server=tcp:" & ServerName & "," & Port & ";")
connString.Append("Initial Catalog = " & Database & "; Persist Security Info=False;")
connString.Append("User ID = " & username & ";")
connString.Append("Password = " & password & ";")
connString.Append("MultipleActiveResultSets = False;")
connString.Append("Encrypt = True;TrustServerCertificate=False;Connection Timeout=30;")
connectionString = connString.ToString
con = New SqlConnection(connString.ToString)
con.Open()
Return con
Catch ex As Exception
Throw
End Try
End Function
Public Shared Function GetConnection(ByVal Servername As String, ByVal DatabaseName As String) As SqlConnection
Dim ConnectString As String
Dim con As SqlConnection
Try
ConnectString = "Data Source=" & Servername & ";Initial Catalog=" & DatabaseName & ";Integrated Security=True"
connectionString = ConnectString
con = New SqlConnection(ConnectString)
con.Open()
Return con
Catch ex As Exception
Throw
End Try
End Function
End class
I can tell that connections are remaining open by running this SQL statement:
SELECT
DB_NAME(dbid) as DBName,
COUNT(dbid) as NumberOfConnections,
loginame as LoginName
FROM
sys.sysprocesses
WHERE
dbid > 0
GROUP BY
dbid, loginame
I set up break points when my DataProxy class is called. I run the SQL code and can see a new connection is opened. Then, I run the code again when I dispose of the DataProxy class and I can see the connection remains. This will build up until it hits 101 connections, then it causes the above error. How am I not handling the connections correctly?

Answer 1

System.InvalidOperationException: 'Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached.'
How am I not handling the connections correctly?
You are "leaking" connections. IE you have some code path that opens a SqlConnection, and doesn't Close/Dispose it. The SqlConnection remains open and is sitting on the managed heap. Eventually it will be GC'd and its Finalizer will close the connection. But if you leak 100 connections before that happens, you get this error.
So you need to ensure that your SqlConnections are always closed using a USING block, or are managed by some other object that's closed with a USING block.
Note that if you are returning a SqlDataReader from a function, there's a special CommandBehavior that will close the SqlConnection when the SqlDataReader is closed.

Answer 2

No, even this code not work and it wait a few minutes to remove sql connection from sql server.
using (var conn = new SqlConnection(connStr))
{
conn.Open();
conn.Close();
}
GC.Collect();
GC.WaitForPendingFinalizers();