{"id":496,"date":"2011-08-28T11:20:00","date_gmt":"2011-08-28T11:20:00","guid":{"rendered":"http:\/\/www.javacodegeeks.com\/2012\/10\/eclipse-memory-analyzer-mat.html"},"modified":"2012-10-21T20:04:36","modified_gmt":"2012-10-21T20:04:36","slug":"eclipse-memory-analyzer-mat","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2011\/08\/eclipse-memory-analyzer-mat.html","title":{"rendered":"Eclipse Memory Analyzer (MAT)"},"content":{"rendered":"
In times past, when it came to tracking down sporadic memory problems in a complex Java application, it required using a commercial product such as JProbe or a lot of painful and inefficient attempts to recreate the issue. Even if the problem were easy to recreate, unless the problem was blatantly obvious, your application might need to be enhanced in an iterative fashion to collect sufficient information to begin to diagnose the problem. And don\u2019t make the rookie mistake of assuming the class\/method\/line that threw the OOM is your problem area. That just happens to be the code that couldn\u2019t obtain the necessary memory.<\/p>\n

Fortunately, now we have a decent free tool that integrates with the Eclipse known as Memory Analyzer, or MAT. Installation can be done via the standard update sites, just type memory analyzer and follow the installation instructions. Charts feature isn\u2019t required if all you want to do is track down your problem areas. And I\u2019ll assume you either have a heap dump generated on an OutOfMemory or have connected to a live vm to extract one. If you don\u2019t have one and the vm is running, you can use MAT to extract one. Just look in File menu, Acquire Heap Dump option.<\/p>\n

When you first open your heap dump, MAT will ask if you\u2019d like to run one of their canned reports.<\/p>\n

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This likely isn\u2019t worth your while. I haven\u2019t found them to provide any meaningful insight. Perhaps if your application is very simple, the problem is obvious or in the case of tuning, the Component Report, these reports might be worth a shot. But likely your best starting point is to take a look at the dominator tree.<\/p>\n

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Either use the icon, the Dominator Tree link under the Biggest Objects by Retained Size section, or select it as an Action.

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First of all, the default Dominator Tree view shows single objects. If nothing jumps out at you immediately, you can take one or both of the following actions.<\/p>\n