Re: [xwiki-users] XWiki going out of resources

Hi XWiki users, fwiw I just want to share my experiences and observations with XWiki instance running out of memory. I was having a hard time to track this down but in the end I could successfully isolate the problem. For quite some time my XWiki instance was getting unresponsive to requests sooner or later. The Wiki was hosted on a VirtualBox VM and in most cases the VM guest was just freezing and needed to be restarted leaving no usable traces in the logs. In some cases I even found JVM crash reports so I first checked different JVMs and VirtualBox versions (PUEL and OSE licences). I had no success with this approach and so I moved the XWiki directly to a host environment (Ubuntu 10.10). I added Server instrumentation (VisualVM) but still the wiki got down after a while. Surprisingly the system was hanging although in many cases there was even enough memory available (I checked different VM settings up to 4GB). Finally a VisualVM thread dump showed what happened: When the robots came visiting my service they query a large number of pages and among them was one user-url: .../XWiki/someUser which ran into an infinite looping condition when rendering the page. I don't know how this could happen but as a result the whole memory was consumed and partly released afterwards so it seemed that there is still enough space available. Once this happened however the Webserver needed to be restarted because it wasn't responsive any more. Since I have deleted this user account everything is running ok for a couple of days now - I still have to move the service back into the VirtualBox guest VM. What puzzles me finally that its possible that one single request can kill the service by going into an infinte rendering loop. I would have thought that at some level there is a depth limit to prevent such conditions.

Hope these observations help someone though ....