How do I compare memory heap dumps in Netbeans?
What I have done is to configure my project to use profiling, then added several profiling points at chosen lines of code (similar to setting breakpoints). These profiling points trigger a "snapshot", which creates a memory dump.
As my application is running, the profiling tab lists each of the profiling points, and marks the number of hits it has encounteed, providing a link to open a report for that profiling point. In addition, the profiler control panel adds the new snapshots to a list.
If I open these reports and follow the links, or open the snapshots from the control panel, in both cases, Netbeans opens a snapshot tab with Summary, Classes, Instances and OQL subscreens.
If I select one of them from the Profiler control panel, and press save, the file gets saved in HPROF format.
If I select the menu Profile --> Compare Memory Snapshots, it only allows me to select NPS format files, of which I cannot obtain any.
I believe Compare Memory Snapshots sounds like it should be able to compare heap dumps, but I cannot figure out how to do it.
Questions
Where is Netbeans putting the NPS files (if it is indeed creating them)? If not how do I get Netbeans to create NPS files triggered from profiling points?
Is there a way to get Netbeans to compare HPROF files, since that is the memory heap dump after all?
Or am I simply completely overlooking something altogether?
Thanks!
Background
Using Netbeans 6.7.1.
I am doing memory profiling for a really large & complex application that has a memory leak problem. I have managed to solve large chunks of the leaks using a combination of Netbeans' profiler & JHAT (command line util that comes with JDK). It's the remaining stragglers that I need a more powerful heap analysis capabilities for - the
hypothesis-first approach that worked previously is becoming decreasingly effective.
This question's really specific, for more background see a question I have asked previously.
Unfortunately, I was not asking for recommendations on other tools which can do this.
I have since found that Netbeans does indeed support comparison of memory heap dumps, but only indirectly. Edit the profiling points such that the "Snapshot" is selected over "heap". This means that Netbeans will produce a .nps file instead of a .hprof file.
The .nps file is Netbean's own proprietary file format, whereas .hprof is the "universal" heap dump format, understood by almost all profiling tools, including JHAT, MAT & Netbeans.
However, the limitation with Netbeans is that it can look at .hprof files, and analyse them, but it cannot compare them to another .hprof file. It can, though, compare one .nps file to another .nps file. However the level of analysis available is limited with .nps files, so that's the trade-off.
So, to answer my own questions:
Where is Netbeans putting the NPS files (if it is indeed creating them)? If not how do I get Netbeans to create NPS files triggered from profiling points?
It is one or the other, you can only choose one per profiling point.
Is there a way to get Netbeans to compare HPROF files, since that is the memory heap dump after all?
No. You cannot compare to HPROF's. The only way to compare the memory at two different points in time appears to be to compare two NPS'es.
I would suggest using eclipse's memory analyzer: http://www.eclipse.org/mat/
I know that you are a netbeans user but mat is actually a standalone application (rcp based) and is capable of loading and comparing hprof files.
I found that it was the best heap analyzer around, particularly with larger heap dumps.
Related
I have a HotSpot JVM heap dump that I would like to analyze. The VM ran with -Xmx31g, and the heap dump file is 48 GB large.
I won't even try jhat, as it requires about five times the heap memory (that would be 240 GB in my case) and is awfully slow.
Eclipse MAT crashes with an ArrayIndexOutOfBoundsException after analyzing the heap dump for several hours.
What other tools are available for that task? A suite of command line tools would be best, consisting of one program that transforms the heap dump into efficient data structures for analysis, combined with several other tools that work on the pre-structured data.
Normally, what I use is ParseHeapDump.sh included within Eclipse Memory Analyzer and described here, and I do that onto one our more beefed up servers (download and copy over the linux .zip distro, unzip there). The shell script needs less resources than parsing the heap from the GUI, plus you can run it on your beefy server with more resources (you can allocate more resources by adding something like -vmargs -Xmx40g -XX:-UseGCOverheadLimit to the end of the last line of the script.
For instance, the last line of that file might look like this after modification
./MemoryAnalyzer -consolelog -application org.eclipse.mat.api.parse "$#" -vmargs -Xmx40g -XX:-UseGCOverheadLimit
Run it like ./path/to/ParseHeapDump.sh ../today_heap_dump/jvm.hprof
After that succeeds, it creates a number of "index" files next to the .hprof file.
After creating the indices, I try to generate reports from that and scp those reports to my local machines and try to see if I can find the culprit just by that (not just the reports, not the indices). Here's a tutorial on creating the reports.
Example report:
./ParseHeapDump.sh ../today_heap_dump/jvm.hprof org.eclipse.mat.api:suspects
Other report options:
org.eclipse.mat.api:overview and org.eclipse.mat.api:top_components
If those reports are not enough and if I need some more digging (i.e. let's say via oql), I scp the indices as well as hprof file to my local machine, and then open the heap dump (with the indices in the same directory as the heap dump) with my Eclipse MAT GUI. From there, it does not need too much memory to run.
EDIT:
I just liked to add two notes :
As far as I know, only the generation of the indices is the memory intensive part of Eclipse MAT. After you have the indices, most of your processing from Eclipse MAT would not need that much memory.
Doing this on a shell script means I can do it on a headless server (and I normally do it on a headless server as well, because they're normally the most powerful ones). And if you have a server that can generate a heap dump of that size, chances are, you have another server out there that can process that much of a heap dump as well.
First step: increase the amount of RAM you are allocating to MAT. By default it's not very much and it can't open large files.
In case of using MAT on MAC (OSX) you'll have file MemoryAnalyzer.ini file in MemoryAnalyzer.app/Contents/MacOS. It wasn't working for me to make adjustments to that file and have them "take". You can instead create a modified startup command/shell script based on content of this file and run it from that directory. In my case I wanted 20 GB heap:
./MemoryAnalyzer -vmargs -Xmx20g --XX:-UseGCOverheadLimit ... other params desired
Just run this command/script from Contents/MacOS directory via terminal, to start the GUI with more RAM available.
I suggest trying YourKit. It usually needs a little less memory than the heap dump size (it indexes it and uses that information to retrieve what you want)
The accepted answer to this related question should provide a good start for you (if you have access to the running process, generates live jmap histograms instead of heap dumps, it's very fast):
Method for finding memory leak in large Java heap dumps
Most other heap analysers (I use IBM http://www.alphaworks.ibm.com/tech/heapanalyzer) require at least a percentage of RAM more than the heap if you're expecting a nice GUI tool.
Other than that, many developers use alternative approaches, like live stack analysis to get an idea of what's going on.
Although I must question why your heaps are so large? The effect on allocation and garbage collection must be massive. I'd bet a large percentage of what's in your heap should actually be stored in a database / a persistent cache etc etc.
This person http://blog.ragozin.info/2015/02/programatic-heapdump-analysis.html
wrote a custom "heap analyzer" that just exposes a "query style" interface through the heap dump file, instead of actually loading the file into memory.
https://github.com/aragozin/heaplib
Though I don't know if "query language" is better than the eclipse OQL mentioned in the accepted answer here.
The latest snapshot build of Eclipse Memory Analyzer has a facility to randomly discard a certain percentage of objects to reduce memory consumption and allow the remaining objects to be analyzed. See Bug 563960 and the nightly snapshot build to test this facility before it is included in the next release of MAT. Update: it is now included in released version 1.11.0.
A not so well known tool - http://dr-brenschede.de/bheapsampler/ works well for large heaps. It works by sampling so it doesn't have to read the entire thing, though a bit finicky.
This is not a command line solution, however I like the tools:
Copy the heap dump to a server large enough to host it. It is very well possible that the original server can be used.
Enter the server via ssh -X to run the graphical tool remotely and use jvisualvm from the Java binary directory to load the .hprof file of the heap dump.
The tool does not load the complete heap dump into memory at once, but loads parts when they are required. Of course, if you look around enough in the file the required memory will finally reach the size of the heap dump.
I came across an interesting tool called JXray. It provides limited evaluation trial license. Found it very useful to find memory leaks. You may give it a shot.
Try using jprofiler , its works good in analyzing large .hprof, I have tried with file sized around 22 GB.
https://www.ej-technologies.com/products/jprofiler/overview.html
$499/dev license but has a free 10 day evaluation
When the problem can be "easily" reproduced, one unmentioned alternative is to take heap dumps before memory grows that big (e.g., jmap -dump:format=b,file=heap.bin <pid>).
In many cases you will already get an idea of what's going on without waiting for an OOM.
In addition, MAT provides a feature to compare different snapshots, which can come handy (see https://stackoverflow.com/a/55926302/898154 for instructions and a description).
In my work, we are running into a difficult to reproduce OOM issue. Or, more accurately, it is very easy to reproduce on one system, making that system unusable, but difficult to reproduce anywhere else, given the same inputs.
The application is being run as a service using a service wrapper. We did manage to get the configuration changed to launch it with the option of outputting a heap dump file on OOM but, unfortunately, they were truncated, most likely due to the service wrapper timing out and killing the process as it wrote the file. This is readily apparent, since the max memory is set to 1GB, and the hprof files are as small as 700MB, which is too small to be the entire heap upon OOM.
It would take a lot of jumping through hoops to additionally configure the wrapper to give the java process a longer time to write out the heap, but we are pursuing this using these 2 options:
wrapper.jvm_exit.timeout=600
wrapper.shutdown.timeout=600
The question is, is there anything useful I can do with the truncated hprof files I have? Eclipse MAT chokes on them. Jhat appears to load them, but then only shows 3 instances of Java.Object of size 0 and nothing else. I tried YourKit and it couldn't write its oids file.
It seems to me like these files should have some useful, accessible information in them. Is there a tool that can read what's there?
Thank you for your time!
Best option for analyzing the dump file which i came across till date, is text editors like vim.
Use Jpofiler(https://www.ejtechnologies.com/products/jprofiler/overview.html). It's not free, but, it has a trial period.
The live memory and CPU view options are your best bet to isolate your issues. It generally runs reasonably well even on large dumps.
The application i am working on suddenly crashed with
java.io.IOException: ... Too many open files
As i understand the issue it means that files are opened but not closed.
Stacktrace of course happens after the fact and can only help understand before what event error occurred.
What would be an intelligent way to search your code base to find this issue which only seems to occur when app is under high stress load.
use lsof -p pid to check what cause leak of file references;
use ulimit -n to see the limit of opened file references of a single process;
check any IO resources in your project,are they released in time?,Note that,File,Process,Socket(and Http connections) are all IO resources.
sometimes, too many threads will cause this problem too.
I think the best way to use a tool specifically designed for the purpose, such as this one:
This little Java agent is a tool that keeps track of where/when/who opened files in your JVM. You can have the agent trace these operations to find out about the access pattern or handle leaks, and dump the list of currently open files and where/when/who opened them.
In addition, upon "too many open files" exception, this agent will dump the list, allowing you to find out where a large number of file descriptors are in use.
I seem to remember YourKit also having some facilities around this, but can't find any specific information at the moment.
What OS? If it's linux/mac, there is information under /proc that should help. On Windows, use the Process Explorer.
As far as searching the code base, perhaps look for code that catches or raises IOException - I think I/O methods that already catch/raise this have a high likelihood of needing a close() call.
Have you tried attaching to the running process using jvisualvm (Java 5.0 and later in the JDK bin directory). You can open the running process and do a heap dump (which if you have an older JDK you will need to analyze using eclipse or intellij or netbeans et. al.).
In JDK 7 the heap dump button is under the "Monitor" tab. It will create a heap dump tab, "Classes" sub-tab that you can check and see if any classes that open files exist in high quantity. Another very useful feature is heap dump compare, so you can take a reference heap dump, let your app run a bit and then take another heap dump and compare the two (the link to compare is on the "[heapdump]" tab you get when you take one. There is also a flag in java for taking a heapdump on crash or OOM exception, you can go down that route if comparing heap dumps does not give you an obvious class that is causing the problem. Also, "Instances" subtab in the heap dump diff will show you what has been allocated in the time between the two heap dumps which may also help.
jvisualvm is an awesome tool that does not get enough mentions.
I'm trying to find memory leaks and performance issues with my java application. Is there a program out there that can help me debug my application and display performance results?
Thanks.
Have a look at jvisualvm in the JDK - a subset of the Netbeans profiler - which can attach to a running Java 6 process and allow you to profile it and do memory analysis.
https://visualvm.dev.java.net/gettingstarted.html
I used a lot of tools to find why my program eats 100+ Mb of ram, polished the code to remove any possible memory leaks. Later I found that once jvm took some memory from the OS, I doesn't always return it, even if that memory is not used, which often looks like a memory leak. This depends on -Xmx and -XX:MaxHeapFreeRatio. I set Xmx to 40 which is roughly how much memory my app should use, and memory usage stays within 10-15 Mb of this range instead of increasing uncontrollably.
Also, jconsole is a great tool. It comes with jdk.
Eclipse has a good memory dump analyzer; but finding a memory leak can be very challenging and requires you to dive deeply into the way the objects are allocated by your application.
It took me 2 full days to figure out that one of my custom JTable cell editor classes was allocating a JDialog upon instantiation, without actually opening it, and the native part of the dialog kept the cell editor instance locked, thus the table, thus the screen and thus all entity objects that were associated with it.
You can try performance inspector tool.Following is the URL.
http://perfinsp.sourceforge.net/
Java Application performance is directly proportional to how JVM is running your application. This tool gives very good profiling information about JVM.But its not a graphical tool,you need to go through the text file generated. But its one time effort and you can get handy with this tool.I used it many time for performance related issues and it helped me lot.
How come every object appears to be marked new, instead of just objects that are in the second snapshot but not in my baseline snapshot? Looking around online, I see some suggestions that I need to use hprof instead of jmap to make my memory dumps, but it appears that hprof generates dumps in exactly the same format.
This is JDK 1.6.0_14; I have tried on both Windows and UNIX.
jhat -baseline indeed won't work with dumps produced by jmap. I'm not certain, but I believe this is because hprof attaches to the JVM right from the start and keeps its own track of objects, allowing it to produce consistent IDs across multiple dumps. Don't quote me on that. Either way, the important point as far as you're concerned is that jmap dumps don't work.
However, all is not lost. Go and get the Eclipse Memory Analyzer. (If you don't use Eclipse, fear not, you can get it as a standalone executable.) It's faster than jhat, uses less memory than jhat and it can do what you want:
Open dump2 (with File|Open Heap Dump). Don't bother having it create a report for you.
Open dump1 (same way). Again, no report.
In the tab for dump2, click "Histogram"
On the right of the toolbar in the Histogram subtab is "Compare to another Heap Dump". Click it.
Select dump1 from your dialog as the dump to use as the baseline.
Presto, you have the differences between dump2 and the baseline dump1.
All of this works fine with a jmap dump.
It seems that you need to use hprof. But are you sure you use the same VM instance ?
The -baseline option allows two dumps to be compared if they were produced by HPROF and from the same VM instance. If the same object appears in both dumps it will be excluded from the list of new objects reported. One dump is specified as a baseline and the analysis can focus on the objects that are created in the second dump since the baseline was obtained.
If everything is considered as new, I will make sure that's the same instance of the VM.
Here