I am creating heap dump using below command:
jmap -dump:file=DumpFile.txt <process-id>
I have opened the generated file - DumpFile.txt but it is not in readable format.
So please let me know how to analyze the data in the generated file.
You should use jmap -heap:format=b <process-id> without any paths. So it creates a *.bin file which you can open with jvisualvm.exe (same path as jmap). It's a great tool to open such dump files.
You can use jhat (Java Heap Analysis Tool) to read the generated file:
jhat [ options ] <heap-dump-file>
The jhat command parses a java heap dump file and launches a webserver. jhat enables you to browse heap dumps using your favorite webbrowser.
Note that you should have a hprof binary format output to be able to parse it with jhat. You can use format=b option to generate the dump in this format.
-dump:format=b,file=<filename>
Very late to answer this, but worth to take a quick look at. Just 2 minutes needed to understand in detail.
First create this java program
import java.util.ArrayList;
import java.util.List;
public class GarbageCollectionAnalysisExample{
public static void main(String[] args) {
List<String> l = new ArrayList<String>();
for (int i = 0; i < 100000000; i++) {
l = new ArrayList<String>(); //Memory leak
System.out.println(l);
}
System.out.println("Done");
}
}
Use jps to find the vmid (virtual machine id i.e. JVM id)
Go to CMD and type below commands >
C:\>jps
18588 Jps
17252 GarbageCollectionAnalysisExample
16048
2084 Main
17252 is the vmid which we need.
Now we will learn how to use jmap and jhat
Use jmap - to generate heap dump
From java docs about jmap
“jmap prints shared object memory maps or heap memory details of a given process or core file or a remote debug server”
Use following command to generate heap dump >
C:\>jmap -dump:file=E:\heapDump.jmap 17252
Dumping heap to E:\heapDump.jmap ...
Heap dump file created
Where 17252 is the vmid (picked from above).
Heap dump will be generated in E:\heapDump.jmap
Now use Jhat
Jhat is used for analyzing the garbage collection dump in java -
C:\>jhat E:\heapDump.jmap
Reading from E:\heapDump.jmap...
Dump file created Mon Nov 07 23:59:19 IST 2016
Snapshot read, resolving...
Resolving 241865 objects...
Chasing references, expect 48 dots................................................
Eliminating duplicate references................................................
Snapshot resolved.
Started HTTP server on port 7000
Server is ready.
By default, it will start http server on port 7000.
Then we will go to http://localhost:7000/
Courtesy : JMAP, How to monitor and analyze the garbage collection in 10 ways
If you use Eclipse as your IDE I would recommend the excellent eclipse plugin memory analyzer
Another option is to use JVisualVM, it can read (and create) heap dumps as well, and is shipped with every JDK. You can find it in the bin directory of your JDK.
VisualVm does not come with Apple JDK. You can use VisualVM Mac Application bundle(dmg) as a separate application, to compensate for that.
MAT, jprofiler,jhat are possible options. since jhat comes with jdk, you can easily launch it to do some basic analysis. check this out
If you just run jmap -histo:live or jmap -histo, it outputs the contents on the console!
Related
I have an taken a core dump file from a machine, with file size 2GB. I can open this file with gdb and see the processes that were running when I took the core file. I want though to convert this file into a heap dump in order to see more useful information. I tried running the below commands without any success. Does anyone have an idea why the file is not converted into heap dump? How can I perform this action?
I tried the bellow commands but I get errors and the file never is being created.
jmap -heap:format=b file=jvmcore.hprof /usr/lib/jvm/jdk1.5.0_22/ jvm.core Usage: jmap \[option\] \<pid\> (to connect to a live java process) or jmap \[option\] \<executable\> \<core\> (to connect to a core file) or jmap \[option\] \[server_id#\]\<remote server IP or hostname\> (to connect to a remote debug server) where option must be one of: \<no option\> to print same info as Solaris pmap \-heap to print java heap summary \-heap:format=b to dump java heap in hprof binary format \-histo to print histogram of java object heap \-permstat to print permanent generation statistics \-h | -help to print this help message
Same result as above i got with the following command:
jmap -heap:format=b file=jvmcore.hprof /usr/lib/jvm/jdk1.5.0_11/ jvm.core
And trying this command gets an error:
jmap -heap:format=b file=jvmcore.hprof jvm.core Attaching to core jvm.core from executable file=jvmcore.hprof, please wait... Error attaching to core file: Can't attach to the core file
With Oracle's Hotspot JVM, it looks like jmap -dump:file=/tmp/dump.txt <pid> can be used to take a heap dump.
However, Eclipse OpenJ9 doesn't include the jmap tool - and if you try to use the regular jmap with OpenJ9's jvm, it gives the exception:
Exception in thread "main" java.lang.ClassCastException: com.ibm.tools.attach.attacher.OpenJ9VirtualMachine incompatible with sun.tools.attach.HotSpotVirtualMachine
at java.lang.ClassCastException.<init>(java.base#10.0.2-adoptopenjdk/ClassCastException.java:71)
at sun.tools.jmap.JMap.executeCommandForPid(jdk.jcmd#10.0.2-adoptopenjdk/JMap.java:128)
at sun.tools.jmap.JMap.dump(jdk.jcmd#10.0.2-adoptopenjdk/JMap.java:192)
at sun.tools.jmap.JMap.main(jdk.jcmd#10.0.2-adoptopenjdk/JMap.java:110)
So, how can one take a heap dump with OpenJ9?
An OpenJ9 heap dump can be created with the command jcmd <PID> Dump.heap <path>.phd.
For example:
jcmd 1 Dump.heap /tmp/heap-dump.phd
Notice:
It must be run as the same user that the JVM is running as.
The PID must be the ID of the JVM process to be inspected. jps -l will list the available processes.
Alternatively, use YourKit to take a memory snapshot:
Download YourKit and extract it
Use the Console Attach Wizard e.g. bash ./YourKit-JavaProfiler-2021.3/bin/attach.sh
Capture a memory snapshot: java -jar ./YourKit-JavaProfiler-2021.3/lib/yjp-controller-api-redist.jar localhost 10001 capture-memory-snapshot
Sources:
Java diagnostic command (jcmd) tool
Support of Portable Heap Dumps (.phd)
YourKit - Command line tool to control profiling
You can use -Xdump:heap:events=user to enable heap dump when signal 3 is passed to OpenJ9 JVM. So, start you application with this option and then issue kill -3 <pid> to get the heap dump.
You can also use Xdump Option Builder tool for generating the -Xdump options based on your requirement.
I think that my Java Program exceeded the usage of memory allowed... this is the error that shows up in Eclipse:
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at Main.main(Main.java:228)
before than trying an implementation with better memory handling, is there any way basically to augment the memory to allocate for the program ? I would like to see the program terminating and showing the result at least.
You can allocate more memory to the process by using the -Xmx flag:
java -Xmx2G YourProgram
Will allocate 2 Gigabytes of memory to the process.
You can do this in Eclipse by going to Run Configurations, the Arguments section and adding -Xmx 2G to the VM arguments.
Increasing memory size is good, but you should also consider that probably your program has some memory leak and you really should bother about it.
You can increase heap size using the cmd-line flags
For example:
java -Xmx6g myprogram
You can get a full list (or a nearly full list, anyway) by typing java -X.
As I don't think your program is using that much memory, I suspect your program is having a memory leak somewhere.
If you could give Main.java:200 till Main.java:250 we could check for any leaks.
If you are sure your program is using that amount of memory you can either run
java -Xmx2G -jar foo.jar in the Command Prompt (Windows) or Terminal (Mac OS X or Linux)
or, if you're running your program in Eclipse under Linux, do the following:
1) Make sure Eclipse is closed
2) Open your favorite text editor at your eclipse.ini file (Default location: /usr/lib/eclipse/eclipse.ini)
3) Search for --Xmx512M and increase this number (i.e. --Xmx2G)
4) Save the file and restart Eclipse
For any explaination about --Xmx and --Xms I refer to Eclipse memory settings when getting "Java Heap Space" and "Out of Memory"
Happy coding :) -Charlie
I have a Memory Dump file and JHAT gives the following message and I cannot analyze anything (as no data is displayed.
Resolving 0 objects...
WARNING: hprof file does not include java.lang.Class!
WARNING: hprof file does not include java.lang.String!
WARNING: hprof file does not include java.lang.ClassLoader!
Does this mean the hprof file is incomplete or corrupt?
I am using
-XX:+HeapDumpOnOutOfMemoryError"
option in my tomcat.
I just came across this same issue with my own heap dump.
jhat shows the warnings you describe, and there's no useful data displayed
Eclipse MAT complains about a NullPointerException
VisualVM can't open the heap dump file at all
It looks like this happens when there is not enough disk space at the time that the heap is dumped, so the file is indeed incomplete/corrupt.
http://forums.oracle.com/forums/thread.jspa?threadID=1175621&tstart=135
I have the same problem today. To clarify, I am using the option heap=sites which is different than a memory dump. I also get the same messages from jhat and jvisualvm. It is possible that jhat does not support reading HPROF files created by heap=sites mode.
I was told I can add the -XX:+HeapDumpOnOutOfMemoryError parameter to my JVM start up options to my JBoss start up script to get a heap dump when we get an out of memory error in our application. I was wondering where this data gets dumped? Is it just to the console, or to some log file? If it's just to the console, what if I'm not logged into the Unix server through the console?
Here's what Oracle's documentation has to say:
By default the heap dump is created in
a file called java_pid.hprof in the
working directory of the VM, as in the
example above. You can specify an
alternative file name or directory
with the -XX:HeapDumpPath= option. For
example -XX:HeapDumpPath=/disk2/dumps
will cause the heap dump to be
generated in the /disk2/dumps
directory.
You can view this dump from the UNIX console.
The path for the heap dump will be provided as a variable right after where you have placed the mentioned variable.
E.g.:
-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=${DOMAIN_HOME}/logs/mps"
You can view the dump from the console on the mentioned path.
I found it hard to decipher what is meant by "working directory of the VM". In my example, I was using the Java Service Wrapper program to execute a jar - the dump files were created in the directory where I had placed the wrapper program, e.g. c:\myapp\bin. The reason I discovered this is because the files can be quite large and they filled up the hard drive before I discovered their location.
If you are not using "-XX:HeapDumpPath" option then in case of JBoss EAP/As by default the heap dump file will be generated in "JBOSS_HOME/bin" directory.
If you only configure -XX:+HeapDumpOnOutOfMemoryError parameter then heapdump will be generated in JBOSS_HOME/bin directory for OpenJDK/Oracle JDK. If you are using IBM JDK then heapdump will be created under /tmp directory as phd file. -XX:HeapDumpPath option gives us more feasibility for configuring our custom headpump path location (-XX:HeapDumpPath=/my-custom-jboss-server-path/). It's recommended to have this parameters configured in your environment as it will collect heapdump on OutOfMemory error for analyzing the issue with memory leak of the application or checking any large object retention in the application.