I have a java.lang.OutOfMemoryError:GC Overhead limit exceeded.
There is no HeapDumpOnOutOfMemoryError command line option for my application.
I need a heap dump but when I try to capture the dump with jmap or jcmd tools they are not responding:
jmap
D:\program>jmap -dump:live,format=b,file=d:\dump4.hprof 8280
Dumping heap to D:\dump4.hprof ...
jcmd
D:\program>jcmd 8280 GC.heap_dump d:\dump6.hprof
8280:
Processes are not completing but dump files are created. When I open them with VisualVM, they are loading infinitely.
If I capture a heap dump of e.g. VisualVM, Tools complete successfully and dumps are created and opened.
Could you please explain why jmap and jcmd are not completing? And how can I capture a dump of the application with OutOfMemoryError exception? Application is still working but there are only a few live threads.
One possibility is that the heap size you intend to dump is too large in size.
Please specify the size of the heap and RAM.
It is not due to your intended heap size is more than allocated heap size. This error occurs when the JVM spent too much time performing Garbage Collection and was only able to reclaim very little heap space. Your application might have ended up using almost all the RAM and Garbage collector has spent too much time trying to clean it and failed repeatedly.
Your application's performance will be slow comparatively, This is because the CPU is using its entire capacity for Garbage Collection and hence cannot perform any other tasks.
Following questions need to be addressed:
What are the objects in the application that occupy large portions of the heap?
In which parts of the source code are these objects being allocated?
You can also use automated graphical tools such as JConsole which helps to detect performance problems in the code including java.lang.OutOfMemoryErrors.
Related
I am new to heap analysis. We have been using spring boot in our web application. Recently heap usage has become too high. To analyse heap dump with tools like Mat and JProfiler, I am downloading it using actuator as follows:
http://localhost:8080/actuator/heapdump
But each time, I am taking heap dump, heap usage is becoming low. I am suspecting may be GC kicks in all that time. Please rectify if I am wrong. So I am not able to capture the actual scenario. Is there any way to take heap dump without triggering GC ? Or is there anyway like whenever heap usage increases more than say 500 MB, heapdump gets generated.
You can have a #Scheduled task to get for you regularly heap usage and generate the 500 MB heapdump. You can use ManagementFactory.getMemoryPoolMXBeans();, it shows the different heap regions and their usage.
To do that externally:
You can use jstat for external monitoring of the heap usage. Wrap it in a script that would analyzse jstat -gc then use jmap to get the heap dump.
I am new to analyzing memory issues in Java. So pardon me if this question seems naive
I have application running with following JVM parameters set:
-Xms3072m -Xmx3072m
-XX:MaxNewSize=1008m -XX:NewSize=1008m
-XX:PermSize=224m -XX:MaxPermSize=224m -XX:SurvivorRatio=6
I am using visualVM to monitor the usage : Here is what I see
The problem is, even when the application is not receiving any data for processing, the used memory doesn't go down. When the application is started, the used space starts low (around 1GB) but grows as the application is running. and then the used memory never goes down.
My question is why the used heap memory doesn't go down even when no major processing happening in application and what configurations can be set to correct it.
My understanding is if application is not doing any processing then the heap used should be less and heap memory available ( or max heap) should remain the same (3GB) in this case.
This is a totally normal trend, even if you believe that it is not used there are probably threads running doing tasks that create objects that are unreferenced once the tasks are done, those objects are eligible for the next GC but as long as there is no minor/major GC they take more and more room in your heap so it goes up until a GC is triggered then you get the normal heap size and so on.
An abnormal trend will be the same thing but after a GC the heap size would be higher than the heap size just after the previous GC which is not the case here.
Your real question is more what my application is doing when is not receiving any data to process? For that a thread dump should help, you can launch jcmd to get the PID then launch jstack $pid to get the thread dump.
Here is an example of a typical trend in case of memory leak:
As you can see the starting heap size has changed between two GC, the new starting heap size is higher than the previous one which may be due to a memory leak.
Problem
We are trying to find the culprit of a big memory leak in our web application. We have pretty limited experience with finding a memory leak, but we found out how to make a java heap dump using jmap and analyze it in Eclipse MAT.
However, with our application using 56/60GB memory, the heap dump is only 16GB in size and is even less in Eclipse MAT.
Context
Our server uses Wildfly 8.2.0 on Ubuntu 14.04 for our java application, whose process uses 95% of the available memory. When making the dump, our buffers/cache used space was at 56GB.
We used the following command to create the dump: sudo -u {application user} jmap -dump:file=/mnt/heapdump/dump_prd.bin {pid}
The heap dump file size is 16,4GB and when analyzing it with Eclipse MAT, it says there are around 1GB live objects and ~14,8GB unreachable/shallow heap.
EDIT: Here is some more info about the problem we see happening. We monitor our memory usage, and we see it grow and grow, until there is ~300mb free memory left. Then it stays around that amount of memory, until the process crashes, unfortunately without error in the application log.
This makes us assume it is a hard OOM error because this only happens when the memory is near-depleted. We use the settings -Xms25000m -Xmx40000m for our JVM.
Question
Basically, we are wondering why the majority of our memory isn't captured in this dump. The top retained size classes don't look too suspicious, so we are wondering if there is something heap dump-related what we are doing wrong.
When dumping its heap, the JVM will first run a garbage collection cycle to free any unreachable objects.
How can I take a heap dump on Java 5 without garbage collecting first?
In my experience, in a true OutOfMemoryError where your application is simply demanding more heap space than is available, this GC is a fool's errand and the final heap dump will be the size of the max. heap size.
When the heap dump is much smaller, that means the system was not truly out of memory, but perhaps had memory pressure. For example, there is the java.lang.OutOfMemoryError: GC overhead limit exceeded error, which means that the JVM may have been able to free enough memory to service some new allocation request, but it had to spend too much time collecting garbage.
It's also possible that you don't have a memory problem. What makes you think you do? You didn't mention anything about heap usage or an OutOfMemoryError. You've only mentioned the JVM's memory footprint on the operating system.
In my experience, having a heap dump much smaller than the real memory used can be due to a leak in the JNI.
Despite you don't use directly any native code, there are certain libraries that use it to speed up.
In our case, it was a Deflater and Inflater not properly ended.
I have an application deployed to production which sometimes throws OutOfMemory exception due to some memory leak. It is running on a headless ubuntu box on which I would prefer not to connect visualvm, jconsole etc remotely. Is there a way to make the jvm do gc (like in visualvm where you just click a button to do it).
I would like to run jmap -histo:live <pid> and this gc commands alternatively to find out which objects are surviving a gc. Which object numbers are growing etc. Right now I can see some unexpected object counts but it is happening across a number of my domain objects so I am not sure if it is a delayed gc or a memory leak.
So in short, I am looking for the linux command to be run against a jvm pid to cause it to do gc. Not system.gc.
The GC will aggressively try to clean up unreferenced objects as the heap gets full. So its not a "delayed gc". I think you are on the right track, use jmap and get a heap dump. Then analyze it to see what application objects are surviving that should not be. You may need to get a couple heap dumps and compare them against each other.
It's pretty hard to get a real memory leak in Java. If you're getting an out of memory error, then it most likely means that you're actually running out of memory. So to fix this, you need to find references to unused objects and clean them up manually. Because otherwise, the garbage collector can't free up the wasted memory.
When the JVM can't allocate any more memory, the garbage collector should automatically run.
I have a Tomcat Application Server that is configured to create a memory dump on OOM, and it is started with -Xmx1024M, so a Gigabyte should be available to him.
Now I found one such dump and it contains only 260MB of unretained memory. How is it possible that the dump is so much smaller than the size he should have available?
Permgen space is managed independently of the heap and can run out even when there's plenty of free memory overall. Some web frameworks (especially JSF) are real hogs and while easily cause the default config to run out. It can be increased with -XX:MaxPermSize=###m
Remember the system space is constrained by the sum of heap and permgen, so you can consume fewer total resources before you start getting the Cannot Create Native Thread OOM exception if you don't decrease heap by the amount PermGen is increased.
Only information about the usage of allocated memory will be dumped to a file.
A heap dump isn't a binary image of your heap, it contains information about data types etc. and may exceed your available memory.
Text (classic) Heapdump file format