Re: Per context heap usage
Robert, On 5/19/22 02:34, Robert Olofsson wrote: On Wed, 2022-05-18 at 17:36 -0400, Christopher Schultz wrote: Is it possible to find out the per deployed context heap usage in tomcat? With a profiler you can look at the retained size of the web application class loader instance associated with a web application. What reference path would lead from a java.lang.String object to the web application ClassLoader? It's allocation-path? That would be tied to the Thread which allocated it, not to the TCCL the Thread happened to have at the time. If you look at a memory dump you can follow the references both up and down Going up means asking "who owns this object" or "what class keeps this object alive". Going down means asking "What fields does this class hold" With modern memory profilers you can aks for the retained set of objects, the profiler will then start from the root objects and go down and calculate how much memory is hanging under each object. Since the jvm heap is a graph with circles this is a bit tricky, but that is for the profile writers to figure out. So if we look at a hypothetical example: Tomcat holds references to one or more classloaders, one per webapp. Each such classloader holds on to a set of servlets. Each servlet holds on to its own resources. So when you look at the retained sets you se something like: Tomcat holds 100% of the memory - Classloader for webapp 1 holds 80% of the memory - Servlet A holds 79% of the memory - Servlet B holds 1% of the memory - Classloader for webapp 2 holds 15% of the memory - classloader for webapp 3 holds 5% of the memory This is of course a simplified example and common things may make the statistics hard to read. Personally I have used both visualvm and eclipse mat to look at memory profiles. Both of them support retained set calculations, but with the last releases of java I have only managed to get visualvm working well. If you get eclipse mat working with this it tends to be a bit more helpful. Hope that makes sense! It does. Thatnks for pointing-out that, in order for the (e.g. String) object to reachable, it must have a reference being held by something else -- and that something was loaded either directly or indirectly from the webapp classloader. Duh. -chris - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: Per context heap usage
On Wed, 2022-05-18 at 17:36 -0400, Christopher Schultz wrote: > > > > > Is it possible to find out the per deployed context heap usage in > > > > > tomcat? > > > > > > > > With a profiler you can look at the retained size of the web > > > > application class loader instance associated with a web application. > > > > What reference path would lead from a java.lang.String object to the web > application ClassLoader? It's allocation-path? That would be tied to the > Thread which allocated it, not to the TCCL the Thread happened to have > at the time. If you look at a memory dump you can follow the references both up and down Going up means asking "who owns this object" or "what class keeps this object alive". Going down means asking "What fields does this class hold" With modern memory profilers you can aks for the retained set of objects, the profiler will then start from the root objects and go down and calculate how much memory is hanging under each object. Since the jvm heap is a graph with circles this is a bit tricky, but that is for the profile writers to figure out. So if we look at a hypothetical example: Tomcat holds references to one or more classloaders, one per webapp. Each such classloader holds on to a set of servlets. Each servlet holds on to its own resources. So when you look at the retained sets you se something like: Tomcat holds 100% of the memory - Classloader for webapp 1 holds 80% of the memory - Servlet A holds 79% of the memory - Servlet B holds 1% of the memory - Classloader for webapp 2 holds 15% of the memory - classloader for webapp 3 holds 5% of the memory This is of course a simplified example and common things may make the statistics hard to read. Personally I have used both visualvm and eclipse mat to look at memory profiles. Both of them support retained set calculations, but with the last releases of java I have only managed to get visualvm working well. If you get eclipse mat working with this it tends to be a bit more helpful. Hope that makes sense! /robo - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: Per context heap usage
Mark, On 5/17/22 12:50, Mark Thomas wrote: On 17/05/2022 17:34, Christopher Schultz wrote: Mark, On 5/17/22 08:17, Mark Thomas wrote: On 17/05/2022 10:41, Thomas Meyer wrote: Hi, Is it possible to find out the per deployed context heap usage in tomcat? With a profiler you can look at the retained size of the web application class loader instance associated with a web application. I don't think this will tell you the volume of objects which belong to those classes, though. If I read a big String into my application, it won't be counted towards the retained size of the web application classloader -- or will it? I don't understand how that String object could count towards the classloader's memory footprint. It should do. The profiler traces obejct references and they should all lead back to the web application class loader. What reference path would lead from a java.lang.String object to the web application ClassLoader? It's allocation-path? That would be tied to the Thread which allocated it, not to the TCCL the Thread happened to have at the time. I've never tried to do this before and I suspect you have, so I'm not trying to say "you're wrong" -- because I know better ;) -- but I'd like to understand what exactly I'm missing, here. -chris - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: Per context heap usage
On 17/05/2022 17:34, Christopher Schultz wrote: Mark, On 5/17/22 08:17, Mark Thomas wrote: On 17/05/2022 10:41, Thomas Meyer wrote: Hi, Is it possible to find out the per deployed context heap usage in tomcat? With a profiler you can look at the retained size of the web application class loader instance associated with a web application. I don't think this will tell you the volume of objects which belong to those classes, though. If I read a big String into my application, it won't be counted towards the retained size of the web application classloader -- or will it? I don't understand how that String object could count towards the classloader's memory footprint. It should do. The profiler traces obejct references and they should all lead back to the web application class loader. Mark - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: Per context heap usage
Mark, On 5/17/22 08:17, Mark Thomas wrote: On 17/05/2022 10:41, Thomas Meyer wrote: Hi, Is it possible to find out the per deployed context heap usage in tomcat? With a profiler you can look at the retained size of the web application class loader instance associated with a web application. I don't think this will tell you the volume of objects which belong to those classes, though. If I read a big String into my application, it won't be counted towards the retained size of the web application classloader -- or will it? I don't understand how that String object could count towards the classloader's memory footprint. -chris - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: Per context heap usage
On 17/05/2022 10:41, Thomas Meyer wrote: Hi, Is it possible to find out the per deployed context heap usage in tomcat? With a profiler you can look at the retained size of the web application class loader instance associated with a web application. Mark - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Per context heap usage
Hi, Is it possible to find out the per deployed context heap usage in tomcat? Mfg Thomas
