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https://issues.apache.org/jira/browse/VELOCITY-223?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12489437
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Nathan Bubna commented on VELOCITY-223:
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So, all told. I think if we drop the static Map for a ReferenceMap (as
Christopher suggested), drop the synchronization (as per the discussion between
Lei and me), and retest to confirm the memory savings then this is ready to go
into the codebase.
> 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,
> StringImagePool.java, VelocityCharStream.java, 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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