[jira] Updated: (VELOCITY-223) VMs that use a large number of directives and macros use excessive amounts of memory - over 4-6MB RAM per form

["Lei Gu (JIRA)" <de...@velocity.apache.org>]

     [ https://issues.apache.org/jira/browse/VELOCITY-223?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Lei Gu updated VELOCITY-223:
----------------------------

    Attachment: 223-patch.txt

Patch fixes for issue 223

Issue number 223, Velocity Engine uses excessive amount of memory when a large number of directives and macros are used.

When a macro or directive is used, they are parsed at run time and the same macro will be parsed every time it is invoked from another macro. This results in an explosion of the duplicated string images. We introduce a string image pool. Before a string image is returned from VelocityCharStream GetImage method, we simply checks against the string image pool. If the string image exists in the pool, we will return the image from the pool. Otherwise we simply return the image itself. We observe a 30% memory footprint reduction after this. 

> VMs that use a large number of directives and macros use excessive amounts of memory - over 4-6MB RAM per form
> --------------------------------------------------------------------------------------------------------------
>
>                 Key: VELOCITY-223
>                 URL: https://issues.apache.org/jira/browse/VELOCITY-223
>             Project: Velocity
>          Issue Type: Bug
>          Components: Engine
>    Affects Versions: 1.3.1
>         Environment: Operating System: All
> Platform: All
>            Reporter: Christian Nichols
>             Fix For: 1.6
>
>         Attachments: 223-patch.txt, AllVelocityMemoryByClass.html, VelocityMemory.JPG
>
>
> Our application FinanceCenter is based on Velocity as the template engine.  We 
> have a library of about 200 macros and about 400 VM files.  Because the 
> velocity parser copies the macro body into the VM during parsing, macros that 
> are frequently used (even though identical and using local contexts) use up 
> large amounts of memory.  On our Linux server (running Redhat 7.2 with Sun JDK 
> 1.4.1_04) we can easily use up over 1GB of RAM simply by opening up many forms 
> (about 150) - the server starts out using 60MB after startup.  This memory 
> times out after 5 minutes and is returned which tells me that it is screen 
> memory.  Our problem is that the NT JVM and Linux JVM (32 bit) are currently 
> limited to about 1.6 - 2.0 GB of ram for heap space.  Thus, using a fair number 
> of forms in the application leaves little space for user session data.
> We have implemented a caching mechanism for compiled templates and integrated 
> it into Velocity so that cached objects are timed out of the cache but the 
> server is still using large amounts of memory.  We finally had to rewrite many 
> of our macros into Java so that memory usage would be reduced (note that these 
> macros were doing complex screen formatting not business logic).  Doing this 
> has reduced our memory by about 30%.  This is currently our biggest issue with 
> Velocity and is causing us to review our decision to stay with Velocity going 
> forward.  This is because we will likely end up with close to 1,000 forms by 
> the end of next year and need to know that Velocity can deal with this.  Is 
> there any work underway to share compiled macro AST's?  This would greatly 
> reduce the amount of memory used.  I have reviewed the parser code that is 
> doing this but it seems that this is an embedded part of the design and not 
> easily changed.

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