[BGOUG] Memory analyzer
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The document discusses Eclipse Memory Analyzer, which is a tool for analyzing heap dumps to detect memory leaks and issues. It begins with some assumptions about the audience's experience and an overview of memory analyzer basics. It then covers topics like how to get a heap dump, the difference between shallow and retained heap, dominator trees, Java reference types, GC roots, and what constitutes a memory leak. The presentation concludes with instructions on how to get involved with the Memory Analyzer community.
[BGOUG] Memory analyzer
- 1. Eclipse Memory Analyzer Krasimir Semerdzhiev Development Architect / SAP Labs Bulgaria
- 2. Agenda Getting started Get hands dirty Q&A © 2011 SAP AG. All rights reserved. 2
- 3. Getting started Few assumptions You’ve passed beyond “Hello World” in Java Hello World apps tend not to require too much memory You’ve gotten an OutOfMemoryError at least once in your life :) You’re proficient already with Garbage Collection Attended the previous BGOUG event GC session © 2011 SAP AG. All rights reserved. 3
- 4. Getting started Memory analyzer basics Works with heap dumps – live snapshots of: © 2011 SAP AG. All rights reserved. 4
- 5. Getting started How to get a heap dump Non-Interactive -XX:+HeapDumpOnOutOfMemoryError On Demand JDK1.4.2_12+ and -XX:+HeapDumpOnCtrlBreak JDK6 and JConsole or VisualVM On IBM VMs -Xdump:system:events=throw,filter=java/lang/OutOfMemoryError, request=exclusive+prepwalk More… http://wiki.eclipse.org/index.php/MemoryAnalyzer#Getting_a_Heap_Dump © 2011 SAP AG. All rights reserved. 5
- 6. Getting started Shallow vs. Retained heap Shallow heap is the memory consumed by one object Retained set of X is the set of objects that will be garbage collected if X is garbage collected Retained heap of X is the sum of shallow sizes of all objects in the retained set of X, i.e. memory kept alive by X Set of elements Retained Set C C, F, G, J K K C, K C, F, G, J, K, I © 2011 SAP AG. All rights reserved. 6
- 7. Getting started Dominator tree An object x dominates an object y if every path in the object graph from the start (or the root) node to y must go through x. In the dominator tree each object is the immediate dominator of its children, so dependencies between the objects are easily identified. © 2011 SAP AG. All rights reserved. 7
- 8. Getting started Dominator tree © 2011 SAP AG. All rights reserved. 8
- 9. Getting started Java references – java.lang.ref Softly reachable Created Initialized Strongly reachable Finalized Weakly reachable Soft reference Phantom reachable GC will try to preserve the object Will collect it prior to throwing OutOfMemoryError Weak reference GC is free to reclaim the object. Phantom reference Track object collections © 2011 SAP AG. All rights reserved. 9
- 10. Getting started GC roots in Java Keeps the objects in heap from being collected by GC System Class Finalizer Queue GC handle Unknown JNI Local Unfinalized Thread stack Unreachable JNI Global Thread block Thread Busy Monitor © 2011 SAP AG. All rights reserved. 10
- 11. Getting started What is a leak? © 2011 SAP AG. All rights reserved. 11
- 12. Agenda Getting started Get hands dirty Q&A © 2011 SAP AG. All rights reserved. 12
- 13. Analyze memory consumption Getting the heap dump: Setup JConsole refuses to connect © 2011 SAP AG. All rights reserved. 13
- 14. Analyze memory consumption DEMO © 2011 SAP AG. All rights reserved. 14
- 15. How to get involved? Eclipse Home Page http://www.eclipse.org/mat/ Forum eclipse.technology.memory-analyzer Blog http://dev.eclipse.org/blogs/memoryanalyzer © 2011 SAP AG. All rights reserved. 15