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From Cedric Dumoulin <ced...@apache.org>
Subject Re: Tiles excessive memory usage
Date Tue, 11 Mar 2003 16:33:30 GMT

Hi Christophe,

    When you develop a software, you often need to choose between 
simplicity, CPU consumption and memory consumption
  In the case of the ComponentContext implementation, and the 
inheritance mechanism, I have chosen the simplicity and the CPU 
consumption.
  Furthermore,  while developping the ComponentContext (tile context) 
and the inheritance mechanism, I have tried to let the class 
ComponentContext independent from the ComponentDefinition class and its 
implementation.
  So, the implementation of ComponentContext create a new Hashmap 
initialized from the definition hashmap. Also, the definition 
inheritance is resolved in a way where each definition has its own 
hashmap referencing all the attributes visible by the definition. Note 
that the attributes themselves are shared between all definitions, they 
aren't copied.
  With this implementation, the access time to an attribute is constant. 
There is no need to check several hashmap. The drawback is the memory 
consumed. This is generally not really a problem on modern servers. The 
memory size is relatively constant because the hashmaps don't grow 
during the application life, they are initialized at startup only.

  Nevertheless, it is certainly possible to find a better compromise 
between the CPU memory consumption and the space memory consumption. For 
example, it is possible to avoid the map creation in the contexts when 
no "locale" attributes are set. Also, it is possible to control the 
definition map sizes, which is not modified once the definition 
inheritances are resolved.

  Maybe you can share with us your application used to do the benchmark 
(with all business stuff removed), and also the methodology used.
 
  Cedric

P.S.:   Je vois que avec le temps tu n'as rien perdu de ton esprit 
critique ;-).

Christophe Warland wrote:

> 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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