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https://issues.apache.org/jira/browse/AMQ-3665?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Torsten Mielke updated AMQ-3665:
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Attachment: AMQ-3665.patch
> Velocity's IntroSpectionCache causes OutOfMemoryError on large AMQ stores
> when running activem-admin journal-audit
> ------------------------------------------------------------------------------------------------------------------
>
> Key: AMQ-3665
> URL: https://issues.apache.org/jira/browse/AMQ-3665
> Project: ActiveMQ
> Issue Type: Bug
> Components: Broker
> Affects Versions: 5.5.1
> Environment: AMQ persistence store, activemq-admin journal-audit
> Reporter: Torsten Mielke
> Labels: OOM, OutOfMemoryError, activmq-admin, journal-audit,
> velocity
> Attachments: AMQ-3665.patch
>
>
> activemq-admin journal-audit can be used to dump the content of the AMQ store
> to system out. The format of the output is rendered using Velocity.
> For large AMQ stores (e.g. 3GB) activemq-admin will run out of memory.
> This is because Velocity internally uses an introSpectionCache that fills up
> over time until heap memory is exhausted.
> There is some documentation on that cache in the Velocity [Developers
> Guide|http://velocity.apache.org/engine/devel/developer-guide.html] in
> section "Other Context Issues":
> {quote}
> One of the features provided by the VelocityContext (or any Context derived
> from AbstractContext) is node specific introspection caching. Generally, you
> as a the developer don't need to worry about this when using the
> VelocityContext as your context. However, there is currently one known usage
> pattern where you must be aware of this feature.
> The VelocityContext will accumulate intropection information about the syntax
> nodes in a template as it visits those nodes. So, in the following situation:
> - You are iterating over the same template using the same VelocityContext
> object.
> - Template caching is off.
> - You request the Template from getTemplate() on each iteration.
> It is possible that your VelocityContext will appear to 'leak' memory (it is
> really just gathering more introspection information.) What happens is that
> it accumulates template node introspection information for each template it
> visits, and as template caching is off, it appears to the VelocityContext
> that it is visiting a new template each time. Hence it gathers more
> introspection information and grows. It is highly recommended that you do one
> or more of the following:
> - Create a new VelocityContext for each excursion down through the template
> render process. This will prevent the accumulation of introspection cache
> data. For the case where you want to reuse the VelocityContext because it's
> populated with data or objects, you can simply wrap the populated
> VelocityContext in another, and the 'outer' one will accumulate the
> introspection information, which you will just discard. Ex. VelocityContext
> useThis = new VelocityContext( populatedVC ); This works because the outer
> context will store the introspection cache data, and get any requested data
> from the inner context (as it is empty.) Be careful though - if your template
> places data into the context and it's expected that it will be used in the
> subsequent iterations, you will need to do one of the other fixes, as any
> template #set() statements will be stored in the outermost context. See the
> discussion in Context chaining for more information.
> - Turn on template caching. This will prevent the template from being
> re-parsed on each iteration, resulting the the VelocityContext being able to
> not only avoid adding to the introspection cache information, but be able to
> use it resulting in a performance improvement.
> - Reuse the Template object for the duration of the loop iterations. Then you
> won't be forcing Velocity, if the cache is turned off, to reread and reparse
> the same template over and over, so the VelocityContext won't gather new
> introspection information each time.
> {quote}
> Right now the Velocity introSpectionCache grows with every entry read from
> the journal until an OOM error is raised.
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