Re: Load Testing Errors

From: Ben Strackany (infoNOSPAM_at_developmentnow.nospam.com)
Date: 11/30/04 

Date: Tue, 30 Nov 2004 09:51:36 -0600

That's exactly what I thought when I read his question. If you are caching a
DataSet/DataTable, and modifying it in your code, that will affect other
threads using that same cached object.

One tip: if you need a DataView from a cached DataTable/DataSet, don't use
DefaultView -- instead always create a new dataview with new
DataView(dtMyCachedDataTable).

Or, maybe he's caching something & not repopulating it when it expires? 

-- 
Ben Strackany
www.developmentnow.com
"Ian Griffiths [C# MVP]" <ian-interact-sw@nospam.nospam> wrote in message
news:uogPzXs1EHA.1076@TK2MSFTNGP09.phx.gbl...
> 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.OnDataBinding(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.OnDataBinding(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
> >
> >
>
>

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