XSL script block dynamic compilation and loading assemblies

[Greg Nagel]

Hi All

I've been experiencing OutOfMemory errors on our prodution webserver for a
few weeks now. I've finally managed to isolate (I think) the problem to our
use of c# script blocks in our xsl files.

While debugging I discovered that the app domain for one of our sites had
13000+ assemblies loaded. I did some digging and it seems that this is as a
result of the xsl user functions being compiled and loaded into memory and
never being unloaded. Unfortunately this happens on our home page which
needs 5 transforms for differing pieces of functionalities.

This is a documented problem: http://support.microsoft.com/kb/316775/en-us.

I've just read this article
(http://blogs.msdn.com/xmlteam/articles/Introducing_XslCompiledTransform.aspx)
over at the xml teams blog and from what I can see this behaviour doesn't
seem to have changed (look under the heading "Cleanup: TemporaryFiles
Property") in .Net 2 (we haven't migrated over to 2 yet, we're still on
1.1).

I've always known that user functions were compiled on the fly into
assemblies. But I never thought the assemblies would be recompiled and
reloaded into memory every time.

Have I made a fundamental design error here? I never heard of this problem,
but it would seem it's never safe to use xsl user functions in a "long
running" app e.g. a web application or service.

I've just read up about ExtensionObjects, should I be using those instead?

Thanks
Greg

[Oleg Tkachenko [MVP]]

Greg Nagel wrote:
> Hi All
>
> I've been experiencing OutOfMemory errors on our prodution webserver for a
> few weeks now. I've finally managed to isolate (I think) the problem to our
> use of c# script blocks in our xsl files.
>
> While debugging I discovered that the app domain for one of our sites had
> 13000+ assemblies loaded. I did some digging and it seems that this is as a
> result of the xsl user functions being compiled and loaded into memory and
> never being unloaded. Unfortunately this happens on our home page which
> needs 5 transforms for differing pieces of functionalities.
>
> This is a documented problem: http://support.microsoft.com/kb/316775/en-us.
>
> I've just read this article
> (http://blogs.msdn.com/xmlteam/articles/Introducing_XslCompiledTransform.aspx)
> over at the xml teams blog and from what I can see this behaviour doesn't
> seem to have changed (look under the heading "Cleanup: TemporaryFiles
> Property") in .Net 2 (we haven't migrated over to 2 yet, we're still on
> 1.1).
>
> I've always known that user functions were compiled on the fly into
> assemblies. But I never thought the assemblies would be recompiled and
> reloaded into memory every time.

They are recompiled each time you reload stylesheet (which is also
something you should avoid).

> Have I made a fundamental design error here? I never heard of this problem,
> but it would seem it's never safe to use xsl user functions in a "long
> running" app e.g. a web application or service.

> I've just read up about ExtensionObjects, should I be using those instead?

Yes, just switch to extension objects.

--
Oleg Tkachenko [XML MVP, MCPD]
http://blog.tkachenko.com | http://www.XmlLab.Net | http://www.XLinq.Net

[Greg Nagel]

Thanks. Switching to extension objects has fixed the problem. Will
definately be using this in the future.

"Oleg Tkachenko [MVP]" <so...@body.com> wrote in message
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