Sending Blob Field To Client In Chunks - Poor Performance On W2K And OS X

I'm using the code below to send files that are in a blob file in my database to the browser client. The code sends the file in chunks in order to increase performance. The file I'm using to test with is 7MB. It works great on Windows XP with any browser. It takes virtually the same amount of time compared to downloading the file directly from the webserver. However, Windows 2000 and Mac OS X both take about 4x the amount of time it takes to download the file on XP machines. Why the performance difference? Is there anything I can do to fix this? I tried downloading the file directly from the webserver instead of getting it out of the database and it takes the same amount of time on all 3 OS. I had the same problem on Windows XP when I wasn't sending the file in chunks, but after using the code below, it started working for XP only.





Dim bufferSize As Integer = 24000


Dim outbyte(bufferSize - 1) As Byte


Dim retval As Long


Dim startIndex As Long = 0





Dim sql As String = "SELECT ..."


Dim cmd As New SqlCommand(sql, conn)


conn.open()


Dim dr As SqlDataReader = cmd.ExecuteReader(CommandBehavior.SequentialAccess)


If dr.Read() Then


' Reset the starting byte for a new BLOB.


startIndex = 0





' Read bytes into outbyte() and retain the number of bytes returned.


retval = dr.GetBytes(DocCol, startIndex, outbyte, 0, bufferSize)


Current.Response.Clear()


Current.Response.Buffer = True


Current.Response.ContentType = "application/octet-stream"


Current.Response.AddHeader("Content-Disposition", "attachment; filename=" & myfile" & "." & myextension)





Do While retval = bufferSize


Current.Response.BinaryWrite(outbyte)


Current.Response.Flush()





' Reposition the start index to the end of the last buffer and fill the buffer.


startIndex += bufferSize


retval = dr.GetBytes(DocCol, startIndex, outbyte, 0, bufferSize)


Loop





'Write the remainder of the last chunk


Dim remaining(retval) As Byte


Array.Copy(outbyte, 0, remaining, 0, retval)


Current.Response.BinaryWrite(remaining)


Current.Response.Flush()


Current.Response.Close()


End If


dr.Close()


conn.Close()