Pooled connection error

dotnet framework


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RE: Pooled connection error

Postby yhhuang » Wed, 25 Jun 2003 15:35:10 GMT

Hello Stephanie,

I didn't see this problem before, so I couldn't tell exactly what happens. 
However, you could try to use the following methods to monitor connection 
pooling in the system:

To monitor your application's use of connection pooling, you can use the 
Profiler tool that ships with SQL Server, or the Performance Monitor tool 
that ships with Microsoft Windows 2000.

To monitor connection pooling with SQL Server Profiler 

1) Click Start, point to Programs, point to Microsoft SQL Server, and then 
click Profiler to start Profiler. 
2) On the File menu, point to New, and then click Trace. 
3) Supply connection details, and then click OK. 
4) In the Trace Properties dialog box, click the Events tab. 
5) In the Selected event classes list, ensure that the Audit Login and 
Audit Logout events are shown beneath Security Audit. To make the trace 
clearer, remove all other events from the list. 
6) Click Run to start the trace. You will see Audit Login events when 
connections are established and Audit Logout events when connections are 

To monitor connection pooling with Performance Monitor 

1) Click Start, point to Programs, point to Administrative Tools, and then 
click Performance to start Performance Monitor. 
2) Right-click the graph background, and then click Add Counters. 
3) In the Performance object drop-down list, click SQL Server: General 
4) In the list that appears, click User Connections. 
5) Click Add, and then click Close. 
Note   The RTM version of the .NET Framework will include an additional set 
of ADO.NET performance counters that can be used in conjunction with 
Performance Monitor to monitor and accumulate connection-pooling statistics 
for the SQL Server .NET Data Provider

Hope it helps.

Best regards,
VS.NET, Visual C++

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!From: "Stephanie" < XXXX@XXXXX.COM >
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!Subject: Pooled connection error
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!After installing VS2003 Frame work 1.1 we are recieving 
!the following error. No application code was changed.
!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.
!I know I can increase the pool size, but doesn't fix the 
!problem.  We are running our application on both an 
!internet and intranet site.  The internet site has not 
!been updated yet and is working fine.  On the intranet we 
!are only about 25 users.
!Any Ideas?
!Thanks, Steph

Re: Pooled connection error

Postby Hildebrandt Nicolas » Thu, 11 Sep 2003 16:18:22 GMT


I have the same issue with the SQLDataAdapter, no matter how many pooled
connections I configure, after some time all connections are drawn from
the pool and the application hangs. The connections seem not to be
returned to the pool after closing (I monitored this behavior on the
performance monitor of Win2K). The only workaround I found was to
disable connection pooling in the connection string. It seems to be a
BUG in ADO.NET. I have tried differend code to fix this, opening and
closing connections explicitely, even setting then the connection object
to Nothing, but always the same result... Any help / BUG fixes

Kind Regards


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Re: Pooled connection error

Postby yhhuang » Thu, 11 Sep 2003 18:30:08 GMT


My suggestion are:

1) Apply asp.net 1.1 and VS.NET 2003(if possilble).
2) Create a simple sample to see if you could repro it.


Best regards,
Yanhong Huang
Microsoft Online Partner Support

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!I have the same issue with the SQLDataAdapter, no matter how many pooled
!connections I configure, after some time all connections are drawn from
!the pool and the application hangs. The connections seem not to be
!returned to the pool after closing (I monitored this behavior on the
!performance monitor of Win2K). The only workaround I found was to
!disable connection pooling in the connection string. It seems to be a
!BUG in ADO.NET. I have tried differend code to fix this, opening and
!closing connections explicitely, even setting then the connection object
!to Nothing, but always the same result... Any help / BUG fixes
!Kind Regards
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Similar Threads:

1.connection in connection pool with pooling=false

I'm finding that even when pooling=false, a connection remains in my
connection pool connected to my database (it seems to quite quickly timeout
though - say 30 seconds).

My connection string:

    Initial Catalog=Benji_UnitTest;Data Source=.;Integrated

Using this setting, I would expect that a new connection be created
everytime, and that when the SqlConnection is close()'d (i.e., returned to
the "pool") that the underlying database connection would be closed.

I also tried setting ";Connection Lifetime=1" in order to get the connection
to close quickly (as a worksround); this didn't seem to affect any change.

Am I misunderstanding something?



2.Leftover Connections in Connection Pool (connection leak)

This never happened before in .NET Framework 1.0 nor .NET Framework
1.1, but connection leak happens if you don't close the connection when
you use SqlTransaction. I would like to share this information with the
MS dev community.

We had this issue of SQL Server performing very poorly while running
our application. My colleague found out that connection leak was
happening whenever the .NET code executed transactions. So I created a
small console program that does a transaction like the following.

Imports System.Data
Imports System.Data.SqlClient

Module Module1

	Sub Main()

		Dim Conn As SqlConnection = GetConnection()
		Dim Trans As SqlTransaction =

		Dim Cmd As New SqlCommand("tblTest_ins", Trans.Connection, Trans)
		Cmd.CommandType = CommandType.StoredProcedure

		For i As Integer = 1 To 50
			Console.WriteLine("Executing stored proc. (" & i.ToString() & ")")
			Dim parTestCol As New SqlParameter()
			With parTestCol
				.ParameterName = "@TestCol"
				.Direction = ParameterDirection.Input
				.SqlDbType = SqlDbType.NVarChar
				.Size = 50
				.SqlValue = "TestValue " & DateTime.Now.ToString()
			End With




		Console.WriteLine("Execution Completed")

		Dim Entry As ConsoleKeyInfo = Console.ReadKey()
		If Entry.Key = ConsoleKey.Y Then
			GoTo Begin
		End If
	End Sub

	Private Function GetConnection() As
		Dim Conn As New
id=sa;password=whatever;Application Name=HelloConnPool;connection
		Return Conn
	End Function

End Module

I ran this code many times, and connection leak was happening. So I
added Conn.Close() right after Trans.Commit(), then the leak was gone.
Well, I could have done Trans.Connection.Close(), but the thing was
that right after the transaction was committed, Connection property was
null. So as we have a data layer that doesn't expose the underlying
connection, we had to define a variable as SqlConnection and hold onto
the reference to the connection from the transaction and the close it
after commit.

I hope I explained this issue well, but this never happened in .NET
Framework 1.1. We converted our code from 1.1 to 2.0, and didn't change
a thing, but this issue came out. I hope this will help people who
experience the same kind of issue. If you have any question, please
just post it here.

3.Trap "connection pool" errors [crosspost from .asp]

"Sean Nolan" < XXXX@XXXXX.COM > wrote in message
news: XXXX@XXXXX.COM ...
> We have implemented unhandled error trapping at the application level and
> log these errors to our database. One error, however, the does not get
> trapped is when the connection pool has exceeded the max number of
> connections.
> Obviously, we need to find the place(s) in our code where connections are
> not closed correctly (espcially in loops), but I'm wondering if it's
> possible to trap this error and to find out which part of our code (i.e.
> stack trace) caused it.

It it possible.  The general idea is to have a object that will be Garbage
Collected in the same pass as your connection.  Whenever a connection is
opened, store the stack trace of the opening method. And put a finalizer on
that object, and write out a trace entry if the finalizer runs and the
connection is still open.

One way to do this is to have a "wrapper object" for your connection.
But then your app code has to create the wrapper instead of the connection.
I think this is a good thing, since you can implement all the DAAB methods
as instance methods of your wrapper object.  But that's another story.

Assuming you are using SQLServer (or some other connection that has a
StateChanged event), there may be an easier way.

Without a wrapper object, to get an object which will be finalized at the
same time as the connection we can use a "spy" object.

If we have a "spy" object which handles the StateChaned event of the
SQLConnection, and we give the spy object a reference to the connection we
will have what we want.  If 2 objects mutually refer to each other, then
they will always be GC'd at the same time.  The spy refers to the
SQLConnection and since the spy handles an event on teh SQLConnection, the
SQLConnection's delegate list contains a reference to the spy object. Voila!

There follows sample program to do this.


Imports System.Data.SqlClient

Class ConnectionFactory
  Private Class ConnectionSpy
    Private con As SqlConnection
    Dim st As StackTrace
    Public Sub New(ByVal con As SqlConnection, ByVal st As StackTrace)
      Me.st = st

      'latch on to the connection
      Me.con = con
      AddHandler con.StateChange, AddressOf StateChange
    End Sub
    Public Sub StateChange(ByVal sender As Object, ByVal args As
      If args.CurrentState = ConnectionState.Closed Then
        'detach the spy object and let it float away into space
        RemoveHandler con.StateChange, AddressOf StateChange
        con = Nothing
        st = Nothing
      End If
    End Sub
    Protected Overrides Sub Finalize()
      'if we got here then the connection was not closed.
      Trace.WriteLine("WARNING: Open SQLConnection is being Garbage
      Trace.WriteLine("The connection was initially opened " & st.ToString)
    End Sub
  End Class

  Public Shared Function OpenConnection(ByVal connect As String) As
    Dim con As New SqlConnection(connect)
    Dim st As New StackTrace(True)
    Dim sl As New ConnectionSpy(con, st)

    Return con
  End Function

End Class

Module Module1

  Sub Main()
    'pipe trace output to the console
    'in your app this would go to a trace file
    Dim connect As String = "..."

    Dim c As SqlConnection = ConnectionFactory.OpenConnection(connect)
    c = Nothing '!!the connection was not closed

    c = ConnectionFactory.OpenConnection(connect)
    c.Close() 'this time it was closed
    c = Nothing

    'output will show 1 warning

  End Sub

End Module

4."General Network Error" and Connection Pooling

I have a very simple WinForms app, that uses a sqlDataAdapter retrieve data 
into a dataset.
The dataset is set to be the datasource of a DataGrid. If - while editing 
rows in my grid - i lose my network connection (or stop + start my 
sqlserver), i get a "General Network Error" when I call my dataAdapters 
.update method. (...naturally, after reestablishing network connection, that 

However, if i disable connection pooling, I get no error. Also, with 
connection pooling enabled, if I repeatedly call update, eventually it 
succeeds on the third attempt.

Anyone who can smarten me up?

J. Jespersen

5.Connection Pooling Error

Hi Mike,

Do you have the call stack for the exception? That would really help us
identify the problem.


Pablo Castro
Program Manager - ADO.NET Team
Microsoft Corp.

This posting is provided "AS IS" with no warranties, and confers no rights.

"Mike Sarbu" < XXXX@XXXXX.COM > wrote in message
news: XXXX@XXXXX.COM ...
> Hi,
> I have a Windows.Forms application (framework 1.1) connected to a SQL
> 2000 Enterprise. I was using connection pooling and the users were getting
> connection pooling errors (25 users, 100 connections in pool). The error
> very random. The exact text of the error is "A connection pooling error
> occurred". It was getting annoying so I disabled connection pooling, but
> they still get the same error.
> Any idea?
> TIA,
> Mike

6. SQL Server connection Pool error in Debug

7. urgent: connection pooling error

8. A connection pooling error has occurred

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