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MemoryAnalyzer

About

The Eclipse Memory Analyzer tool (MAT) is a fast and feature-rich heap dump analyzer that helps you find memory leaks and analyze high memory consumption issues.

With Memory Analyzer one can easily

  • find the biggest objects, as MAT provides reasonable accumulated size (retained size)
  • explore the object graph, both inbound and outbound references
  • compute paths from the garbage collector roots to interesting objects
  • find memory waste, like redundant String objects, empty collection objects, etc...

Getting Started

Installation

See the download page for installation instructions.

Basic Tutorials

Both the Basic Tutorial chapter in the MAT documentation and the Eclipse Memory Analyzer Tutorial by Lars Vogel are a good first reading, if are just starting with MAT.

Further Reading

Check MemoryAnalyzer/Learning Material. You will find there a collection of presentations and web articles on Memory Analyzer, which are also a good resource for learning.


Getting a Heap Dump

HPROF dumps from Sun Virtual Machines

The Memory Analyzer can work with HPROF binary formatted heap dumps. Those heap dumps are written by Sun HotSpot and any VM derived from HotSpot. Depending on your scenario, your OS platform and your JDK version, you have different options to acquire a heap dump.

Non-interactive

If you run your application with the VM flag -XX:+HeapDumpOnOutOfMemoryError a heap dump is written on the first Out Of Memory Error. There is no overhead involved unless a OOM actually occurs. This flag is a must for production systems as it is often the only way to further analyze the problem.

As per this article, the heap dump will be generated in the "current directory" of the JVM by default. It can be explicitly redirected with -XX:HeapDumpPath= for example -XX:HeapDumpPath=/disk2/dumps . Note that the dump file can be huge, up to Gigabytes, so ensure that the target file system has enough space.


Interactive

As a developer, you want to trigger a heap dump on demand. On Windows, use JDK 6 and JConsole. On Linux and Mac OS X, you can also use jmap that comes with JDK 5.

Via MAT:

Via Java VM parameters:

  • -XX:+HeapDumpOnOutOfMemoryError writes heap dump on OutOfMemoryError (recommended)
  • -XX:+HeapDumpOnCtrlBreak writes heap dump together with thread dump on CTRL+BREAK
  • -agentlib:hprof=heap=dump,format=b combines the above two settings (old way; not recommended as the VM frequently dies after CTRL+BREAK with strange errors)

Via Tools:

  • Sun (Linux, Solaris; not on Windows) JMap Java 5: jmap -heap:format=b <pid>
  • Sun (Linux, Solaris; Windows see link) JMap Java 6: jmap.exe -dump:format=b,file=HeapDump.hprof <pid>
  • Sun (Linus, Solaris) JMap with Core Dump File: jmap -dump:format=b,file=HeapDump.hprof /path/to/bin/java core_dump_file
  • Sun JConsole: Launch jconsole.exe and invoke operation dumpHeap() on HotSpotDiagnostic MBean
  • SAP JVMMon: Launch jvmmon.exe and call menu for dumping the heap

Heap dump will be written to the working directory.

Vendor / Release VM Parameter VM Tools
On OoM On Ctrl+Break Agent JMap JConsole
Sun, HP
1.4.2_12 Yes Yes Yes
1.5.0_07 Yes Yes (Since 1.5.0_15) Yes Yes (Only Solaris and Linux)
1.6.0_00 Yes Yes Yes Yes
SAP
1.5.0_07 Yes Yes Yes Yes (Only Solaris and Linux)

System Dumps and Heap Dumps from IBM Virtual Machines

Memory Analyzer can also read memory-related information from IBM system dumps and from Portable Heap Dump (PHD) files. For this purpose one just has to install the IBM DTFJ feature into Memory Analyzer version 0.8 or later. Follow the IBM DTFJ feature installation instructions. If the DTFJ feature is successfully installed then 'File' 'Open Heap Dump' should give the following options for the file types:

  • All known formats
  • HPROF binary heap dumps
  • IBM Javacore file
  • IBM Portable Heap Dump
  • IBM Portable Heap Dump (gzipped)
  • IBM SDK for Java (J9) JExtract output XML
  • IBM SDK for Java (J9) JExtracted system dump
  • IBM SDK for Java (J9) system dump
  • IBM SDK for Java (J9) JExtracted system dump
  • IBM SDK for Java 1.4.2 JExtracted system dump


Minimum-required versions of IBM Virtual Machines to generate the dump are:

IBM JDK 1.4.2 SR12, 5.0 SR8a and 6.0 SR2

though previous versions may generate dumps usable with Memory Analyzer but with inaccurate root information.

The IBM Diagnostics Documentation contains details about how to trigger a system dump.

IBM Java 5.0 and Java 6 Virtual Machine dump options

A quick reference for IBM Java 5.0 and Java 6 Virtual Machine command line options:

  • -Xdump:system+heap+java:events=systhrow+user,filter=java/lang/OutOfMemoryError,request=exclusive+prepwalk+compact

Dump types:

  • system - a system process dump. Process system dump files with jextract before loading them into Memory Analyzer. Do not give them a .sdff extension as that is only used for Java 1.4.2 system dumps
  • heap - a Portable Heap Dump (PHD) file. Contains all objects and classes, but no thread details
  • javacore - a readable file which contains information about class loaders and which can be used by Memory Analyzer when reading PHD files

Events:

  • systhrow - when a system generated exception is thrown
  • user - the user has typed control-break

Filter:

  • java/lang/OutOfMemoryError - the type of the systhrow exception

Request:

  • exclusive Stop anything modifying the heap while generating the dump
  • prepwalk Make sure the heap is safe to dump
  • compact minimise the size of the heap
IBM Java 1.4.2 dump options

A quick reference for IBM Java 1.4.2 dump options

  • export JAVA_DUMP_OPTS=ONOUTOFMEMORY(SYSDUMP,HEAPDUMP,JAVADUMP)
  • set JAVA_DUMP_OPTS=ONOUTOFMEMORY(SYSDUMP,HEAPDUMP,JAVADUMP)

On non-z/OS systems process any system dump files with JExtract to give a .sdff file. On z/OS systems copy the SVC dump file in binary mode to your Eclipse Memory Analyzer system, giving it a .dmp file extension.

IBM Support Assistant

The latest version 4.1 of IBM Support Assistant has a technical preview of IBM Monitoring and Diagnostic Tools for Java - Memory Analyzer which contains version 0.8 of Eclipse Memory Analyzer together with the latest IBM DTFJ feature packaged for IBM Support Assistant.

Previous versions of Memory Analyzer

A previous old version of Memory Analyzer, version 0.7, required both a DTFJ Adapter feature and a DTFJ feature. It is strongly recommended that you upgrade to the current Memory Analyzer. If for some reason you cannot do this then follow the installation instructions for the old IBM DTFJ Adapter feature and back level IBM DTFJ feature. If you have DTFJ problems then there is an update for just the DTFJ feature. Follow the IBM DTFJ feature installation instructions for the latest level of DTFJ.

What if the Heap Dump is NOT Written on OutOfMemoryError?

Heap dumps are not written on OutOfMemoryError for the following reasons:

  • Application creates and throws OutOfMemoryError on its own
  • Another resource like threads per process is exhausted
  • C heap is exhausted

As for the C heap, the best way to see that you won't get a heap dump is if it happens in C code (eArray.cpp in the example below):

   # An unexpected error has been detected by SAP Java Virtual Machine:
   # java.lang.OutOfMemoryError: requested 2048000 bytes for eArray.cpp:80: GrET*. Out of swap space or heap resource limit exceeded (check with limits or ulimit)?
   # Internal Error (\\...\hotspot\src\share\vm\memory\allocation.inline.hpp, 26), pid=6000, tid=468

C heap problems may arise for different reasons, e.g. out of swap space situations, process limits exhaustion or just address space limitations, e.g. heavy fragmentation or just the depletion of it on machines with limited address space like 32 bit machines. The hs_err-file will help you with more information on this type of error. Java heap dumps wouldn't be of any help, anyways.

Also please note that a heap dump is written only on the first OutOfMemoryError. If the application chooses to catch it and continues to run, the next OutOfMemoryError will never cause a heap dump to be written!

Extending Memory Analyzer

Memory Analyzer is extensible, so new queries and dump formats can be added. Please see MemoryAnalyzer/Extending_Memory_Analyzer for details.

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