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From <cwill...@maine.rr.com>
Subject Re: Tiles excessive memory usage
Date Mon, 10 Mar 2003 23:22:14 GMT
Chris,

I'm just now getting to profiling our struts/tiles app and have always had some concern about
the efficiency of the tiles.  Not that I'm a suspecting type of person but I just didn't have
any information and that caused me to wonder.

Regardles when or if this fix gets placed in a release, would you be willing to offer sufficient
code snippets that will give me enough understanding to implement your fix in my app?  I'm
now getting deeper into tiles and getting a good feel for what's going on so this would be
a perfect time for me before we enter client phase.  Also, I'd be willing to contribute this
efficiency gain to the project(with your help or ok) if Cedric and the other powers agree
this is something that should be done.

But in the meantime, could you supply me with some more detailed information and snippets.
 This could potentially kill my project since performance is the major hot word amoung manager
types these days where I work.  You can reply to cwilling@maine.rr.com with details that don't
pertain to the developer's group if you like.

Thanks for posting this!!!!!!!

Chris Willingham
  ----- Original Message ----- 
  From: Christophe Warland 
  To: 'struts-dev@jakarta.apache.org' 
  Cc: 'cedric@apache.org' ; 'cedric.dumoulin@lifl.fr' 
  Sent: Monday, March 10, 2003 4:47 PM
  Subject: Tiles excessive memory usage


  At my company, we have been recently forced to patch Tiles to solve some major memory problems
where Tiles was eating a lot of memory for no apparent reasons. We wish to share our findings
with you. And we will be happy to send our code change to Cedric if he wishes so. 

  Here are some quick numbers about our J2EE runtime after complete bootup (appserver and
EAR file are up, deployed and ready to serve HTTP requests):
   - With original Tiles code: 79 MB of RAM is used
   - After our custom code change: 28 MB of RAM is used

  Note that the Tiles version that we use is an old one (our source zip shows 09/10/2001).
However, a quick analysis of the more recent Tiles source found in Struts 1.1 RC1 shows that
most the code where the defect lies is still in there. But we haven't actually been able to
confirm the problem at runtime since our app is not compatible with the latest Struts and
Tiles development.

  Here are a few excerpt of our internal analysis so that you can understand the issue.

  --

  Our application does not actually make use of the Tiles template mechanism but instead builds
on top of Tiles' i18n concept to offer localized Web pages based on an individual's language,
country, personality and channel. We make extensive use of Tiles Component definitions and
inheritance in XML files, and 667 out of the 668 definitions used by our app inherit from
another one.

  With the help of a Java profiler, we showed that 64% of the 79 MB of memory was used by
HashMap entries created by Tiles.  This corresponds to 50.5 MB of RAM. After close investigation,
it turns out that the very useful Tiles' component inheritance has been mis-implemented. 

  Our application has only one definition that doesn't extend another one: the root "pageDefinition",
which contains common information such as "pageCopyrightLink" for example. Other Component
Definitions that extend "pageDefinition", such as "disbursementCB", do not need to repeat
this information. When queried for the "pageCopyrightLink" value, the "disbursementCB" component
will delegate the processing to its parent component, in this case "pageDefinition".

  Unfortunately, this handy conceptual delegation is actually not implemented in a similar
way in the Tiles source code.

  In our example, when the "disbursementCB" component is instantiated in memory, the Tiles
source code does not pass it a reference to the parent "pageDefiniton" component. Instead,
Tiles forces the new "disbursementCB" component to make a deep copy of all values defined
in its parent(s). This means that, ultimately, our application ends up with 668 copies of
the "pageCopyrightLink" value in memory, instead of one. 

  After modification of the Tiles source code so that true delegation is actually happening
in memory at runtime, new heap allocation statistics showed that the problem with excessive
usage of HashMap$Entry has been completely solved. The most in-use object in the JVM is now
of the type "[C", a common and normal trend in typical Java applications.

  The total amount of memory was also down to 28 MB. This is a pleasant 51 MB gain over the
previous result.

  --

  Finally, without being too demanding, we would appreciate if a patched version of Tiles
could be made available for for both the upcoming Struts 1.1 release and the current stabe
Strust 1.0.2 one.


  Best Regards,


  Christophe Warland


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