Re: Tomcat arbitrarily freezes
Hi! five days after my first question and no answer in sight. To bad. So far, we have switched from JDK 1.4.2 to JDK 1.5 and from Tomcat 5.0.27 to 5.5.4 and the problem persists. However, while under JDK 1.4.2 it was always the thread with id #2 under JDK 1.5 it is still the thread VM Thread, but now under id #4. Using the better debugging features of JDK 1.5 (jstack, jmap) we could pin down the problem in more detail: whenever the problem starts, the output of jstack and jmap shows that these debugging-tools have more and more problems to give information about certain memory areas. When the problem reaches its climax, a bug number of memory areas are marked by jstack with an Error occurred during stack walking:-Message or by jmap with UnmappedAddressException. You see, at the moment we are only guessing what problem we have here. Maybe someone has an idea how to analyze the problem more properly or even know how to solve it (without changing some of the components like using another servlet container engine or another JVM). Thank you for any help, Oliver Schoenwald University of Hagen Germany Oliver Schoenwald wrote: Our system configuration is as follows: SUN Fire 240 with 2 cpus at 1.28 GHz (Sparc-3) 8 GB RAM Solaris 9 (with actual patches) All requests are handled via Apache 2.0.52 with mod_ssl and using mod_jk2. The system works well most of the time, but seemingly randomly the catalina process starts to use up more and more cpu performance without actually doing anything useful! Memory usage stays normal/stable, so we analyzed the process and found out the following: - The cpu performance is used up primarily by the thread VM Thread. - This Thread is running nothing else but synchronization primitives, which where called very fast an in high numbers without reading or writing anything (as if it is in some kind of endless loop of doing nothing). - The effect (and an symptome which can be monitored repeatedly) is that the number of threads that the catalina process is using rises with every new request, because no thread gets enough cpu power to come to an end. VM Thread is taking away anything after a short period of time. We monitored the machine with prstat -L to see when the cpu usage of the catalina process rose to a unusual high value (5% at average, rising up to about 60% when VM Thread got into its frenzy). So we could see that one single lwp was going into the high cpu usage. As soon as we could see the rise in cpu usage we used pstack to find out which thread is responsible for the lwp-id that was shown by prstat -L. Then, we used kill -3 to create a thread-dump of the catalina-process and searched for the thread-number that was stated by pstack. That thread-dump showed us that the thread called VM Thread seems to be the problematic thread. - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Tomcat arbitrarily freezes
On Tue, 11 Jan 2005 13:51:13 +0100, Oliver Schoenwald [EMAIL PROTECTED] wrote: Hi! five days after my first question and no answer in sight. To bad. So far, we have switched from JDK 1.4.2 to JDK 1.5 and from Tomcat 5.0.27 to 5.5.4 and the problem persists. However, while under JDK 1.4.2 it was always the thread with id #2 under JDK 1.5 it is still the thread VM Thread, but now under id #4. Using the better debugging features of JDK 1.5 (jstack, jmap) we could pin down the problem in more detail: whenever the problem starts, the output of jstack and jmap shows that these debugging-tools have more and more problems to give information about certain memory areas. When the problem reaches its climax, a bug number of memory areas are marked by jstack with an Error occurred during stack walking:-Message or by jmap with UnmappedAddressException. You see, at the moment we are only guessing what problem we have here. Maybe someone has an idea how to analyze the problem more properly or even know how to solve it (without changing some of the components like using another servlet container engine or another JVM). If you don't get any answers, it is that people don't have any ideas and / or nothing useful to say. For example, this is the first time I hear about a problem with this internal VM thread. While other Tomcat arbitrarily freezes issues are well known on some OSes, this one is brand new to me. You seem to assert that this is a common problem encountered by many people, and you also seem certain that your problems come for that (which means bad luck, as this is an internal VM thread). Can you give links giving more details about this ? -- x Rémy Maucherat Developer Consultant JBoss Group (Europe) SàRL x - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Re: Tomcat arbitrarily freezes
... there is always a chance to have hardware problems (bad memory chip) so the error will occur when memory consumption increases. - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
Tomcat arbitrarily freezes
Hello, we are using Tomcat 5.0.27 to provide the eLearning environment of our University. Our system configuration is as follows: SUN Fire 240 with 2 cpus at 1.28 GHz (Sparc-3) 8 GB RAM Solaris 9 (with actual patches) All requests are handled via Apache 2.0.52 with mod_ssl and using mod_jk2. The system works well most of the time, but seemingly randomly the catalina process starts to use up more and more cpu performance without actually doing anything useful! Memory usage stays normal/stable, so we analyzed the process and found out the following: - The cpu performance is used up primarily by the thread VM Thread. - This Thread is running nothing else but synchronization primitives, which where called very fast an in high numbers without reading or writing anything (as if it is in some kind of endless loop of doing nothing). - The effect (and an symptome which can be monitored repeatedly) is that the number of threads that the catalina process is using rises with every new request, because no thread gets enough cpu power to come to an end. VM Thread is taking away anything after a short period of time. To come to this information, we did the following: We monitored the machine with prstat -L to see when the cpu usage of the catalina process rose to a unusual high value (5% at average, rising up to about 60% when VM Thread got into its frenzy). So we could see that one single lwp was going into the high cpu usage. As soon as we could see the rise in cpu usage we used pstack to find out which thread is responsible for the lwp-id that was shown by prstat -L. Then, we used kill -3 to create a thread-dump of the catalina-process and searched for the thread-number that was stated by pstack. That thread-dump showed us that the thread called VM Thread seems to be the problematic thread. As far as we found out that problems occured several times with Tomcat 5 for other users in the world. However, so far no one offered an explanation what is going wrong there and what could be done to avoid that problem. We now have prepared a monitoring service that kills and restarts the catalina engine as soon as the problem occurs, but that solution is not a good one. Any suggestions of how to solve the problem are very, very welcome. If you need more information or have any idea how we should analyze the situation more properly, I would be happy to hear of it. Thank you in advance, Oliver Schoenwald FernUniversitaet Hagen Germany - To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
