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This article describes the usage of the Eclipse Memory Analyzer (MAT) to identify memory leaks.

1. Analyzing memory leaks with Eclipse

1.1. The Eclipse Memory Analyser (MAT) tooling

The Eclipse Memory Analyser Tooling (MAT) is a set of plug-ins for the Eclipse IDE which provides tools to analyze heap dumps from Java application and to identify memory problems in the application. This helps the developer to find memory leaks and high memory consumption issues.

It visualizes the references to objects based on Java heap dumps and provides tools to identify potential memory leaks.

1.2. Using heap dumps to get a snapshot of the memory of an application

A heap dump is a snapshot of the complete Java object graph on a Java application at a certain point in time. It is stored in a binary format called HPROF.

It includes all objects, fields, primitive types and object references.

2. Installation

Install Eclipse MAT via the Help ▸ Install New Software…​ menu entry. Select the update site of your release from the drop-down box and once its content is downloaded, select General Purpose Tools and its sub-entries Memory Analyzer and Memory Analyzer(Charts).

Installation of MAT

3. Creating heap dumps for Java programs

It is possible to instruct the JVM to create automatically a heap dump in case that it runs out of memory, i.e. in case of a OutOfMemoryError error. To instruct the JVM to create a heap dump in such a situation, start your Java application with the -XX:+HeapDumpOnOutOfMemoryError option.

Use the File ▸ New ▸ Other…​ ▸ Other ▸ Heap Dump menu entry to open a dialog to select for which process you want to acquire a memory dump.

Creating a heap dump

Select the process for a heap dump in the following dialog and press the Finish button.

Alternatively you can also interactively create a heap dump via Eclipse. For this, open the Memory Analysis perspective via Perspective ▸ Open Perspective ▸ Other…​.

Opening the MAT perspective

If you trigger the creation of the heap manually the JVM performs sa garbage collector run before it writes the heap dump.

4. Use the Eclipse Memory Analyzer

4.1. Reviewing a heap dump

After a new heap dump with the .hprof ending has been created, you can open it via a double-click in Eclipse. If you used MAT to create the heap dump, it should be opened automatically.

You may need to refresh your project (F5 on the project). Double-click the file and select the Leak Suspects Report.

Opening a leak report

The overview page allows you to start the analysis of the heap dump. The dominator tree gives quickly an overview of the used objects.

Opening the dominator tree

In the dominator tree you see the references which are hold.

MAT dominator tree

To find which element is holding the reference to this object, select the entry and select Find shortest path to GC root from the context menu.

4.2. Analyzing Android heap dumps with Eclipse

Android allows to create heap dumps of an application’s heap. This heap dump is stored in a binary format called HPROF. To create a heap dump use the Dump HPROF file button in the DDMS Perspective.

The Android heap dump format is similar to the Java heap dump format but not exactly the same. Eclipse MAT can work directly with the Android heap dump format.

5. Example

5.1. Create Project

Create the Java project called com.vogella.mat.first and the com.vogella.mat.first package. Create the following class.

package com.vogella.mat.first;

import java.util.ArrayList;
import java.util.List;

public class Main {

        /**
         * @param args
         */
        public static void main(String[] args) {
                List<String> list = new ArrayList<String>();
                while (1<2){
                        list.add("OutOfMemoryError soon");
                }

        }

}

5.2. Create heap dump and analysis

In Eclipse add the -XX:+HeapDumpOnOutOfMemoryError to the runtime configuration.

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Run the project. It crashes and writes an heap dump.

Open the heap dump in MAT and get familiar with using the MAT tooling.

6. jconsole

You can also interactively create a heap dumps via the jconsole, a tool which is included in the JDK. Type jconsole in the command line to start it.

To allow a Java program the access of jconsole use the -Dcom.sun.management.jmxremote start option.

Use them MBeans | com.sun.management | HotSpotDiagnostics | Operations |DumpHeap .

More info can be found in JConsole and JConsole Tutorial.

7. About this website

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Copyright © 2012-2016 vogella GmbH. Free use of the software examples is granted under the terms of the EPL License. This tutorial is published under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Germany license.

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