I have a Web Service that returns very large string object. The string
contais xmldata fetched directly from sql server by using xml explicit.
The thing here is that if I get xml-document  that is 11mb without web
service it takes about 2 minutes. With web service it takes about 5min.
This is acceptable. But when I get 37mb document without web service it
takes about 5-6min but with web service it takes about 50min! As you
can see this doesn't quite match up... The calls are excactly the same,
so the problem isn't there. On the bigger document sqlserver does a
little more work, but still (according to task manager) it's the web
service that takes 80-90% of the time.

The call is like this:
       Dim ws As New webservice
       ws.Timeout = System.Threading.Timeout.Infinite
       str = ws.getData
       Dim sw As StreamWriter = New StreamWriter("c:\Temp\data.xml",
False)
       sw.Write(str)
       sw.Close()

and the web service is like this:
           Dim conn As New SqlConnection(connstr)
           Dim sqlcom As New SqlCommand
           Dim sqlre As SqlDataReader

           sqlcom.CommandType = CommandType.StoredProcedure
           sqlcom.Connection = conn
           sqlcom.CommandTimeout = 1200
           sqlcom.CommandText = "getData"
           conn.Open()
           sqlre =
sqlcom.ExecuteReader(CommandBehavior.CloseConnection)
           While sqlre.Read
               str = str & sqlre(0)
           End While
          --then close and return str

I've also tried it like this:
   Private connec As ADODB.Connection
   Private comm As New ADODB.Command
   <XmlIgnore()> Private objStream As New ADODB.Stream
   <XmlIgnore()> Public str As String

------

           connec = Me.GetConnection()
           comm.CommandType = CommandType.StoredProcedure
           comm.CommandTimeout = 1200
           comm.ActiveConnection = connec
           comm.CommandText = "getData"
           objStream.Open()
           comm.Properties("Output Stream").Value = objStream
           objStream.Position = 0
           comm.Execute(, , 1024)
           str = objStream.ReadText
           --then close and return str

but it's the same with this way too. Webmethod also has the
"BufferResponse:=False" set. The return object could be xmldocument
also, but if I've understood correctly returning string is better and
then construct the xmldocument on client-side. The webservice is on
localhost. Does anyone have any ideas why it's taking so long and maybe
how it could be fixed?