We have a web site where we use velocity to generate our HTML pages. Recently I was asked to help troubleshoot some performance issues and the root cause of our problem was that the velocity cache had grown to well over 1GB in size causing the JVM to continuously GC to try to free up memory.
As a short term fix I have grabbed the 1.5 beta ResourceCacheImpl class so that a maximum cache size can be set and enforced. Unfortunately when this was done the performance of the site degraded significantly as the pages were continuously compiled. I used the YourKit memory profiler and found the following information about the individual velocity cache entries (see attached picture): Name Cache Size File Size --------------------------------------------------- VM_framework_library.vm 9,596,472 130,500 VM_buttons_library.vm 1,195,680 39,113 VM_layout_library.vm 1,683,256 54,371 admin/AdminHome.vm 32,505,168 979 poNewGrid.vm 14,399,648 753 poTemplateGrid.vm 14,369,000 774 po/details.vm 11,140,952 8,368 sub.vm 10,115,096 24,576 At this time we have made a very heavy investment in velocity as our presentation layer framework and love it. In order to meet our performance goals, we need to keep as many of the velocity pages in cache as we can but if we do that, we can only fit 2 web applications per Tomcat deployment in a 32 bit environment. In searching through the JIRA issues, I found ( http://issues.apache.org/jira/browse/VELOCITY-450 ) and ( http://issues.apache.org/jira/browse/VELOCITY-223 ) that reference this exact issue as well as the wiki entry talking about how to reduce the memory footprint. I am sending email to the developers list offering up my time to assist with this issue. I was hoping that there would be someone who would be able to point me in a direction to get me started and that there would potentially be some "big wins" that we could take advantage of. Are there any places where velocity is hanging on to strings, tokens, or processing instructions where we could potentially free them up? Are there other ways of factoring macros, files, or #parses that will help in reducing the footprint? Is there potentially extra data in any of the AST classes that isn't necessary after parsing or is potentially duplicate? Thank you, Ryan Smith <<VelocityMemory.JPG>>
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