There is a Java Struts application running on Tomcat, that have some memory errors. Sometimes it becomes slowly and hoard all of the memory of Tomcat, until it crashes.
I know how to find and repair "normal code errors", using tests, debugging, etc, but I don't know how to deal with memory errors (How can I reproduce? How can I test? What are the places of code where is more common create a memory error? ).
In one question: Where can I start? Thanks
EDIT:
A snapshot sended by the IT Department (I haven't direct access to the production application)
Use one of the many "profilers". They hook into the JVM and can tell you things like how many new objects are being created per second, and what type they are etc.
Here's just one of many: http://www.ej-technologies.com/products/jprofiler/overview.html
I've used this one and it's OK.
http://kohlerm.blogspot.com/
It is quite good intro how to find memory leaks using eclipse memory analyzer.
If you prefer video tutorials, try youtube, although it is android specific it is very informative.
If your application becomes slowly you could create a heap dump and compare it to another heap dump create when the system is in a healthy condition. Look for differences in larger data structures.
You should run it under profiler (jprofile or yourkit, for example) for some time and see for memory/resource usage. Also try to make thread dumps.
There are couple of options profiler is one of them, another is to dump java heap to a file and analyze it with a special tool (i.e. IBM jvm provides a very cool tool called Memory Analizer that presents very detailed report of allocated memory in the time of jvm crash - http://www.ibm.com/developerworks/java/jdk/tools/memoryanalyzer/).
3rd option is to start your server with jmx server enabled and connect to it via JConsole with this approach you would be able to monitor memory ussage/allocation in the runtime. JConsole is provided with standard sun jdk under bin directory (here u may find how to connect to tomcat via jconsole - Connecting remote tomcat JMX instance using jConsole)
Related
We have a major challenge which have been stumping us for months now.
A couple of months ago, we took over the maintenance of a legacy application, where the last developer to touch the code, left the company several years ago.
This application needs to be more or less always online. It's developed many years ago without staging and test environments, and without a redundant infrastructure setup.
We're dealing with a legacy Java EJB application running on Payara application server (Glassfish derivative) on an Ubuntu server.
Within the last year or two, it has been necessary to restart Payara approximately once a week, and the Ubuntu server once a month.
This is due to a memory leak which slows down the application over a period of around a week. The GUI becomes almost entirely non-responsive, but a restart of Payara fixes this, at least for a while.
However after each Payara restart, there is still some kind of residual memory use. The baseline memory usage increases, thereby reducing the time between Payara restarts. Around every month, we thus do a full Ubuntu reboot, which fixes the issue.
Naturally we want to find the memory leak, but we are unable to run a profiler on the server because it's resource intensive, and would need to run for several days in order to capture the memory leak.
We have also tried several times to dump the heap using "gcore" command, but it always result in a segfault and then we need to reboot the Ubuntu server.
What other options / approaches do we have to figure out which objects in the heap are not being garbage collected?
I would try to clone the server in some way to another system where you can perform tests without clients being affected. Could even be a system with less resources, if you want to trigger a resource based problem.
To be able to observe the memory leak without having to wait for days, I would create a load test, maybe with Apache JMeter, to simulate accesses of a week within a day or even hours or minutes (don't know if the base load is at a level where that is feasible from the server and network infrastructure).
First you could set up the load test to act as a "regular" mix of requests like seen in the wild. After you can trigger the loss of response, you can try to find out, if there are specific requests that are more likely to be the cause for the leak than others. (It also could be that some basic component that is reused in nearly any call contains the leak, and so you cannot find out "the" call with the leak.)
Then you can instrument this test server with a profiler.
To get another approach (you could do it in parallel) you also can use a static code inspection tool like SonarQube to analyze the source code for typical patterns of memory leaks.
And one other idea comes to my mind, but it is coming with many preconditions: if you have recorded typical scenarios for the backend calls, and if you have enough development resources, and if it is a stateless web application where each call could be inspoected more or less individually, then you could try to set up partial integration tests where you simulate the incoming web calls, with database and file access, but if possible without the application server, and record the increase of the heap usage after each of the calls. Statistically you might be able to find out the "bad" call this way. (So this would be something I would try as very last option.)
Apart from heap dump have to tried any realtime app perf monitoring (APM) like appdynamics or the opensource alternative like https://github.com/scouter-project/scouter.
Alternate approach would be to analyse existing application issue Eg: Payara issues like these https://github.com/payara/Payara/issues/4098 or maybe the ubuntu patch you are currently running app on.
You can use jmap, an exe bundled with the JDK, to check the memory. From the documentation:-
jmap prints shared object memory maps or heap memory details of a given process or core file or a remote debug server.
For more information you can see the documentation or see the stackoverflow question How to analyse the heap dump using jmap in java
There is also a tool called jhat which can be used tp analise java heap.
From the documentation:-
The jhat command parses a java heap dump file and launches a webserver. jhat enables you to browse heap dumps using your favorite webbrowser. jhat supports pre-designed queries (such as 'show all instances of a known class "Foo"') as well as OQL (Object Query Language) - a SQL-like query language to query heap dumps. Help on OQL is available from the OQL help page shown by jhat. With the default port, OQL help is available at http://localhost:7000/oqlhelp/
See JHat Dcoumentation, or How to analyze the heap dump using jhat
This might be a long shot of a question, but I have ran into a very complicated issue and I am unsure on how to solve it.
Long story short, we have a Java application running, it's currently using JDBC to pull in data from a MysQL Database on startup.
We have had a meltdown and that database is no longer active and has been lost forever and so has the data to go along with it which internally is very valuable.
However the data is still stored in the heap of the running JVM that pulled it in.
My only hope now is to somehow extract the data from the running JVM, in an ideal world i would be able to attach to it and have the flexibility to run code which could access the internal running classes..
So my questions today are:
Is my approach reasonable and possible?
If so how can I attach to the JVM and 'Inject' code
Thank you for reading
It seems that what you want to use is the jmap command. jmap can be used to dump the heap of a running JVM into a file, which you can then analyze "off-line", using tools such as jhat or JVisualVM.
It allows you to do so without killing the JVM and/or injecting code into it, and since the heap dump file is "inert", you can analyze it at your leisure without fear of harming the running VM by probing it further. Admittedly, I haven't used it extensively, so I'm not sure exactly what its capabilities are, but theoretically, you could perhaps also use JVisualVM's OQL language to run automated sequences on data in the heap and dump it to files in a format you want.
See, for instance, this question for usage examples.
In a situation like this the Eclipse Memory Analyzer Tool can be a good solution. It works on heap dumps too and shows you which objects take up memory.
In addition to this it can show the content of objects / memory locations.
I sometimes found MAT goes beyond what VisualVM does, but perhaps a view like this helps you find your data already:
(This is a screenshot of a made-up example where I create some custom objects in
order to show them with their value in the heapdump)
Perhaps you can even attach Eclipse to the running application. There is a certain trick where you can run custom code in a breakpoint. This one could somehow dump your data to disk.
I've written a Java file, using Jsp,servlets, that I would like to perform run-time tests on. I've never done this before and was just curious on how to go about it.
What I'm interested in knowing, besides the actual timings, is how to find cpu,memory and io utilization when running the application.Your thoughts are appreciated.
Typically you wouldn't measure these from within the application, but by running another tool on the same host.
If you just want to see the impact on the host operating system, you can use a program like top (on *nix boxes), or good old Task Manager on Windows, to see the CPU/memory/IO utilisation of your Java process (typically the servlet container such as Tomcat).
If you want more detailed information on the actual Java process itself, you can connect JConsole or jvisualvm to get VM information (including memory and CPU) for the process itself. (With Java 6 you should be able to do this from the local machine without passing any parameters to the Java process at startup; for Java 5, or remote connections, you'll need to pass command-line arguments to the Java process to allow (remote) JMX connections.)
Finally, if you want really in-depth details of the resource usage, down to the performance of various methods (which it sounds like you're after), you'll need to use a profiler. There are several of these for Java - with YourKit and JProfiler being the biggest commercial ones (in my unqualified opinion). I believe that the NetBeans IDE also has a decent profiler built-in. The process for connecting these to your application would vary depending on the app itself, but these will all typically allow you to "drill down" into the CPU time to see which classes/methods took the most cycles to execute, and likewise to drill down into memory use to see which classes are taking up the most memory.
The standard way to monitor running Java applications these days is sing JMX through the JConcole
If your a using a commercial application server like Weblogic or WebSphere these have custom and powerful management consoles that provide the monitoring information you are looking for. The technology at the heart of these consoles is still JMX so these can also be monitored and managed using the standard JConsole. This article shows how to do this for Weblogic.
I guess you need this info in the client side (browser). So it's not Java based question.
If so, here is my answer:
I prefer using FireBug and ySlow extensions. They give performance information, memory information and much more.
I combine it with using regular task-manager to view more information about the browser.
BR
I have an application running on Websphere Application Server 6.0 and it crashes nearly every day because of Out-Of-Memory. From verbose GC is certain there are the memory leaks(many of them)
Unfortunately the application is provided by external vendor and getting things fixed is slow & painful process. As part of the process I need to gather the logs and heapdumps each time the OOM occurs.
Now I'm looking for some way how to automate it. Fundamental problem is how to detect OOM condition. One way would be to create shell script which will periodically search for new heapdumps. This approach seems me a kinda dirty. Another approach might be to leverage the JMX somehow. But I have little or no experience in this area and don't have much idea how to do it.
Or is in WAS some kind of trigger/hooks for this? Thank you very much for every advice!
You can pass the following arguments to the JVM on startup and a heap dump will be automatically generated on an OutOfMemoryError. The second argument lets you specify the path for the heap dump file. By using this at least you could check for the existence of a specific file to see if a heap dump has occurred.
-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=<value>
I see two options if you want heap dumping automated but #Mark's solution with heap dump on OOM isn't satisfactory.
You can use the MemoryMXBean to detect high memory pressure, and then programmatically create a heap dump if the usage (or usage delta) seems high.
You can periodically get memory usage info and generate heap dumps with a cron'd shell script using jmap (works both locally and remote).
It would be nice if you could have a callback on OOM, but, uhm, that callback probably would just crash with an OOM error. :)
Have you looked at JConsole ? It uses JMX to give you visibility of a variety of JVM metrics, including memory info. It would probably be worth monitoring your application using this to begin with, to get a feel for how/when the memory is consumed. You may find the memory is consumed uniformly over the day, or when using certain features.
Take a look at the detecting low memory section of the above link.
If you need you can then write a JMX client to watch the application automatically and trigger whatever actions required. JConsole will indicate which JMX methods you need to poll.
And alternative to waiting until the application has crashed may be to script a controlled restart like every night if you're optimistic that it can survive for twelve hours..
Maybe even websphere can do that for you !?
You could add a listener (Session scoped or Application scope attribute listener) class that would be called each time a new object is added in session/app scope.
In this - you can attempt to check the total memory used by app (Log it) as as call run gc (note that invoking it will not imply gc will always run)
(The above is for the logging part and gc based on usage growth)
For scheduled gc:
In addition you can keep a timer task class that runs after every few hrs and does a request for gc.
Our experience with ITCAM has been less than stellar from the monitoring perspective. We dumped it in favor of CA Wily Introscope.
Have you had a look on the jvisualvm tool in the latest Java 6 JDK's?
It is great for inspecting running code.
I'd dispute that the you need the heap dumps when the OOM occurs. Periodic gathering of the information over time should give the picture of what's going on.
As has been observed various tools exist for analysing these problems. I have had success with ITCAM for WebSphere, as an IBMer I have ready access to that. We were very quickly able to indentify the exact lines of code in out problem situation.
If there's any way you can get a tool of that nature then that's the way to go.
It should be possible to write a simple program to get the process list from the kernel and scan it to see if your WAS process is still running. On a Unix box you could probably whip up something in Perl in a few minutes (if you know Perl), not sure how difficult it would be under Windows. Run it as a scheduled task every five minutes or so, and if the process doesn't show up you could have it fork off another process that would deal with the heap dump and re-start WAS.
A Java application I support that runs on JRE 1.4.2_12 is hanging near midnight every night. I'd like to try and record as much profiling information as I can to discover if there is an issue in the JVM or external to the app.
I'd like to use HPROF to collect as much information as possible.
Is there a way to have HPROF dump its cpu sample and memory allocation report every minute instead of at the termination of the JVM?
Is there a different, more appropriate profiler that can collect information like this?
Rather than relying on dump files, I would try hooking up a profiler to the VM and leave it attached until the hang up occurs. Then use the profiler to introspect the state of the threads.
The use of Java 1.4 is a minor issue here, since 1.4's debug interface is not great, but some profilers still support it. I can particularly recommend YourKit, which is commercial, but offers an evaluation licence. It's the best profiler I've used, but some margin.
First things first: did you analyze the thread dump when your application hangs? A lot of the time that has enough information to troubleshoot a hanging java app...
Ctrl-Break in the process window on Windows, or kill -QUIT [pid] on Linux.
I would first try to determine if its actually your app or something else.
Are there any other apps on the box, if so do they run any batch around midnight. It could be a situation of your app suffering from a lack of resources due to other things running on the box or chewing up bandwidth.
Was this always the case or did it start recently. If this is new look at what changed on the box as a whole not just your own app.