I've started to debug my software using visualVM. I only started to get familliar with this software.
I have memory leak. I found sth that is suspected, but dont know what to make of it.
What is the next step?
This is the way I use Java visualVM to quickly trace memory leaks.
First setup breakpoint or pause in your code at places you want to inspect.
Perform Heap Dumps of your program, use "show in instances view" to view instances in detail for classes you suspect to leak (i.e. obviously too much instances in memory).
Then identify one instance of that class that should have been collected. In the "references" panel, you can see all the objects that refer to your class, right click on "this" and select "nearest GC root", this will show you what references prevent the class from being collected by the GC.
This way you can quickly identify where is the wrong reference and modify your program accordingly to avoid the leak.
Good luck, it's actually very interesting task and if you are a beginner you will learn a lot about how the JVM works
I do not know anything about your application but I would suspect the memory leak can be traced back to a HashMap. Values often accumulate in maps (for caching...).
Also have a look at these similar posts:
VisualVM memory leak detection
How to find memory leaks using visualvm
Related
I seems to have memory leak problems in my javaFX application, i have been using the net beans profiler tool to help me locate the source of the leaks but i have hit a wall as I'm not sure exactly what I'm doing.
now i have looked at tutorials,and they say to monitor the surviving generations of a object but I'm still unsure what to with this information. I have taken a screenshot of the highest surviving generation objects while i was monitoring my application.
Can someone explain to me what exactly i should be doing with these objects or are they actually causing a memory leak?
A common source of unexpected high memory usage is adding objects to a collection and then not removing them when you are done (I see the image you posted shows a HashMap that may be an issue). The typical solution is to use a collection which will not keep an object alive once all other references to it are gone, see WeakHashMap for more info.
To dig into these types of issues further capture a hrpof (you can use VisualVM, JConsole, etc.) and then analyze it in Eclipse MAT or a similar tool.
How can I determine the memory usage for referenced objects only in java? ie. exclude "dead" objects from memory usage during the running of a Java application.
I want to display this information and trigger an alert if it reaches a certain threahold. I also want to use this to measure how much memory is taken up when a file is imported into my application.
My application consists of many processes that all run at the same time of which one of them imports files into memory and then into a database. if I measure memory usage using the Runtime.getRuntime.freeMemory or MemoryPoolMXBean and with all the other processes running, memory usage goes up and up because of these processes and because the GC isn't running "in real time" the memory usage depicts dead objects as well as referenced ones. This is not a clear indication for me as to what is taking up memory at the time.
Is there a way to determine memory used by referenced objects only at any time?
You can look into JConsole and see if that suits your need.
There is also VisualVM.
They let you monitor the app but I am not sure how you can do that in your own application to trigger an alarm once your memory is low.
Also, you can use WeakReference and SoftReference if you want objects to be garbage-collected quicker.
I found a good article on how to query the size of a Java Object. It is slightly long so I cannot post any of it here. However, here is the link: http://www.javamex.com/tutorials/memory/instrumentation.shtml Here is a SO question on the same topic determining java memory usage
Click for:
JConsole
VisualVM
you can use eclipse memory analyzer MAT.
I am trying to detect the memory leaks in my java application using VisualVM. I am using the VisualVM 1.3.5.
I followed the steps which should be said in this tutorial http://rejeev.blogspot.in/2009/04/analyzing-memory-leak-in-java.html
After following those steps, I don't know where I have to start edit my code. Is there any way to find the java class and the line number where the memory was leaked to correct the code.
Or any one suggest me a good way to find memory leaks using the VisualVM.
Good answers are definitely appreciated .
No profiling tool will give you the line where a potential memory leak is concurring.
Profiling an application takes a bit more effort than that. Usually, a tool like VisualVM will, for instance, show you what type of Objects are being instantiated the most, and that can indicate where the problem is.
For instance, if a huge amount of byte[] objects are being created, perhaps you're not closing the Input/Output streams you are creating?
There is no silver bullet to find memory leaks, it takes effort and some practice, and is completely application dependent.
That being said, this link might help as well:
http://www.kdgregory.com/index.php?page=java.outOfMemory
I am looking into how to use JConsole to detect memory leaks.
I see that in Memory Pool in my MBeans I can define UsageThreashold for my Tenured Generation.
So if my application exceeds this threashold the heap memory becomes red in the Memory tab.
Question: How does this help? I mean how am I supposed to use this setting to analyze my memory? How am I supposed to figure out this value?
In my opinion I don't think that UsageThreashold parameter is the most helpful for you to detect memory leaks (but if someone knows some tricks with it, please do share). In my experience that parameter is more helpful to visually understand if my application is getting way too near my max heap size and I'm in danger of getting an OutOfMemoryException.
Still regarding using JConsole to search for memory leaks, I don't think there's a silver bullet for the process. But what I usually do is the following:
If exists a memory leak, it means that the objects (the ones that are leaking) won't get collected, hence, your Tenured Generation won't fully recover after any amount of GCs.
With the application running I connect JConsole and try to spot a leak by observing the memory tab, if after several computations of my application and also after various GCs occurring (including pressing the Perform GC button, which will result in a full gc) the memory never goes below, or at least to the memory value, it started tracking there's a great possibility that something is leaking. When the leak is big, you can even see a "stair graph" pattern in your memory.
Keep in mind that if your application has long computations running, which may consume memory this analyzes must be done carefully. You must understand when those processes have finished. For example, just run one of those computations and track the total evolution of memory, before, during and afterwards.
Also, I suggest you to try visualVM instead, because it also allows you to create heap dumps, which you can use in order to understand which objects are still in memory and explore the references graph to understand why they are not being collected.
you can use JMAP to see the histogram and/or to create heap dumps and study your memory consumption with tools like Eclipse MAT or YourKit.
JConsole is used more for monitoring and running MBeans and less for analysis and in my expirence JVisualvm is better for that since you can use it for sampling your code and see what methods are CPU consuming.
I have been working on this project on Java with multiple modules. Since quite some time, I have been occasionally getting "java: Out Of Memory" error! I am pretty new to this 'popular' error and wanted to know the general approach to solve such errors.
Also, are there standard tools accepted by the industry to help figure out the cause of such errors?
The modules in my project include every minute polling from a third party (using web service), multi-threading among other things. However, this is just a pointer and I seek a general approach and not something very specific to my project.
Thanks.
Sometimes you just have an class that uses a lot of memory and you need to increase the heap size or make a more space-efficient algorithm. Other times it is a leak and you need to deference objects.
Run jvisualvm (it's included in the JDK).
Connect to your process and try if you can to recreate the
out-of-memory error while keeping an eye on the heap size.
Perform a heap dump when the memory grows large. Search for the
largest objects by size - often that will give you the culprit
class.
Look at the dependencies to see what is holding a references. If it is a memory leak make sure to dereference unneeded objects.
Also, are there standard tools accepted by the industry to help figure out the cause of such errors?
Yes, there are memory profilers such as VisualVM and YourKit. I use the latter extensively, for both CPU and memory profiling, and find it extremely useful. To get some idea of what it's capable of, take a look at this page: link.
If you can't increase the available memory you have to consume less.
Don't keep references to Objects that you don't need at the time of execution (like data you can reload dynamically) and if necessary redesign your flow (e.g. don't process all objects in parallel and do it sequentially) to require less memory at that time. The garbage collection should do the rest for you.
Especially if you load big data objects into memory consider to use a streaming approach if possible. E.g. you don't need to load a whole file into memory if you want to search through it. You can just step through it.
Besides architectural problems you can also have leaks: keeping unintentional references to objects you don't need anymore. Since they are referenced, the garbage collector can't free the memory and you run out of memory at some point. That is probably the #1 reason for OutOfMemoryExceptions and it usually has to do with static references since classes and therefore the statics are usually not unloaded after the first time you touch a class. The internet has many articles on finding / fixing those, e.g. How to Fix Memory Leaks in Java
one tool I know of is MAT
You likely have a memory leak. Finding it is a challenge. Netbeans has some tools to help you profile the VM . You can profile your project and view men usage while it runs. Apache JMeter is also available as a plug-in or you can run it on its own.
JMeter.apache.org
If you get OOM too often, then start java with correct options, get a heap dump and analyze it with jhat or with memory analyzer from eclipse (http://www.eclipse.org/mat/)
-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=<path to dump file>