This is not normal for a heavily loaded application - ASP.NET can quite
happily put up with continuous heavy loads, as can SQL Server. These
problems are indicative of programming errors.
There are many reasons an application might fail under load when it normally
works, but the two main ones you run into most often are:
* multithreading problems
* resource starvation issues
I notice your exception is occurring inside a DataView. So this makes me
wonder if perhaps it is the first one - are you sharing a single DataSet
instance in your application?
I've seen problems when using a DataSet to cache information at the
application level. You can do this, but you need to make sure that only one
thread at a time uses the DataSet in question. (This is rather tricky if
you're binding to the DataSet, as you appear to be doing in this case - you
would need to enforce sequential access to the DataSet around your call to
DataBind.)
An easy mistake to make with the DataSet is to think "I'm only reading data
from this DataSet, so I don't need multi-threading protection."
Unfortunately, anything that uses views onto the DataSet (e.g. data binding)
does in fact modify the internal index cache of the DataTables in the
DataSet, even if you're only reading data. I've seen code fail with
NullReferenceException errors for exactlyt this reason when reading from a
DataSet on multiple threads in the past, which is why I mention this.
So if you are sharing data in static (or Shared) fields or are using the
Application state, then it could well be a multithreading thing.
Alternatively, there may be some resource that you're running out of when
the system is under load, and you're not detecting this condition correctly,
or are not taking the correct steps to avoid the problem. However, I'm not
quite sure what could be happening that that would result in the errors you
have posted, so I can't offer a useful hypothesis.
Another possibility is that there's something about the way you're using the
database that means you're just getting unexpected results when lots of
stuff is happening concurrently. The errors suggest that you're expecting
to see data but that it's missing. Perhaps you're getting null values back
from your request when you were expecting non-null values. It is
conceivable that you might see such a problem if you failed to use a
transaction when one was necessary - a database request that works fine when
the system is not under load can return inconsistent or unexpected results
under heavy load if it doesn't ensure that its work is isolated through
transactions.
(In other words, just because your request happens to work on an idle system
doesn't mean that the request is bug-free.)
But whatever the problem is, this is not 'normal' - .NET web servers don't
simply start throwing random exceptions under load. ASP.NET is a lot more
robust than that!
--
Ian Griffiths -
http://www.interact-sw.co.uk/iangblog/
DevelopMentor -
http://www.develop.com/
"Shabam" wrote:
A web application of mine developed using C# + MS SQL runs fine normally.
However when I stress test it with a load testing software (using about 60
simultaneous users) some instances start erroring out. I see two
different
errors. One is a "Object reference not set to an instance of an object."
error, which appears to always contain the same information, and the other
is a "There is no row at position X.", where X is a number.
Is this an indication of bad coding or is this just a normal consequence
of
overloading a web application? How can the above two errors happen when
the
server is being overloaded when normally the application works fine?
ERROR #1:
Server Error in '/' Application.
----------------------------------------------------------------------------
----
Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the
current web request. Please review the stack trace for more information
about the error and where it originated in the code.
Exception Details: System.NullReferenceException: Object reference not set
to an instance of an object.
Source Error:
An unhandled exception was generated during the execution of the current
web
request. Information regarding the origin and location of the exception
can
be identified using the exception stack trace below.
Stack Trace:
[NullReferenceException: Object reference not set to an instance of an
object.]
System.Data.DataView.GetRecord(Int32 recordIndex) +22
System.Data.DataView.IsOriginalVersion(Int32 index) +9
System.Data.DataRowView.GetColumnValue(DataColumn column) +23
System.Data.DataColumnPropertyDescriptor.GetValue( Object component) +25
System.Web.UI.DataBinder.GetPropertyValue(Object container, String
propName) +72
System.Web.UI.DataBinder.GetPropertyValue(Object container, String
propName, String format) +11
System.Web.UI.WebControls.ListControl.OnDataBindin g(EventArgs e) +403
System.Web.UI.Control.DataBind() +26
FN.advancedsearch.populateListcontrols()
FN.advancedsearch.Page_Load(Object sender, EventArgs e)
System.Web.UI.Control.OnLoad(EventArgs e) +67
System.Web.UI.Control.LoadRecursive() +35
System.Web.UI.Page.ProcessRequestMain() +750
ERROR #2:
Server Error in '/' Application.
----------------------------------------------------------------------------
----
There is no row at position 5.
Description: An unhandled exception occurred during the execution of the
current web request. Please review the stack trace for more information
about the error and where it originated in the code.
Exception Details: System.IndexOutOfRangeException: There is no row at
position 5.
Source Error:
An unhandled exception was generated during the execution of the current
web
request. Information regarding the origin and location of the exception
can
be identified using the exception stack trace below.
Stack Trace:
[IndexOutOfRangeException: There is no row at position 5.]
System.Data.DataView.GetRecord(Int32 recordIndex) +60
System.Data.DataView.IsOriginalVersion(Int32 index) +9
System.Data.DataRowView.GetColumnValue(DataColumn column) +23
System.Data.DataColumnPropertyDescriptor.GetValue( Object component) +25
System.Web.UI.DataBinder.GetPropertyValue(Object container, String
propName) +72
System.Web.UI.DataBinder.GetPropertyValue(Object container, String
propName, String format) +11
System.Web.UI.WebControls.ListControl.OnDataBindin g(EventArgs e) +403
System.Web.UI.Control.DataBind() +26
FN.advancedsearch.populateListcontrols()
FN.advancedsearch.Page_Load(Object sender, EventArgs e)
System.Web.UI.Control.OnLoad(EventArgs e) +67
System.Web.UI.Control.LoadRecursive() +35
System.Web.UI.Page.ProcessRequestMain() +750
