Memory Analyzer Tool (MAT)
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The document details a memory analyzer tool presented by Mohammad Samiullah Farooqui, covering essential concepts of memory analysis, such as heap dumps, shallow and retained heaps, and memory leak identification methods. It outlines how to analyze memory leaks by examining the dominator tree and provides specific strategies to optimize memory usage. Additionally, it includes resources for further learning on memory analysis techniques.
Memory Analyzer Tool (MAT)
- 1. MEMORY ANALYZER TOOL BY MOHAMMAD SAMIULLAH FAROOQUI
- 2. AGENDA • Memory Analysis • Some definitions • Example of leak code • Demo of MAT
- 3. Why use MAT • Identify memory leaks • Reduce memory consumption
- 4. Important Definitions • Heap Dump • Shallow Heap • Retained Heap • Dominator Tree • Garbage Collection Roots
- 5. Heap Dump • a snapshot of the memory of a Java process • contains information about the java objects and classes in the heap 1. All Objects - Class, fields, primitive values and references 2. All Classes - Classloader, name, super class, static fields 3. Garbage Collection Roots - Objects defined to be reachable by the JVM 4. Thread Stacks and Local Variables - The call-stacks of threads at the moment of the snapshot, and per frame information about local objects • MAT works with HPROF binary heap dumps
- 6. How to acquire a Heap Dump
- 7. Shallow Heap • memory consumed by one object
- 8. Retained Heap • Retained set of X is the set of objects which would be removed by GC when 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.
- 10. 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. • The immediate dominator x of some object y is the dominator closest to the object y.
- 11. Object graph to Dominator Tree
- 12. Garbage Collection Roots • A garbage collection root is an object that is accessible by the JVM(DVM in case of Android) Examples:- 1. System Class(Class loaded by bootstrap/system class loader) For example, java.util.* 2. Java Local(Local variable) For example, input parameters or locally created objects of methods that are still in the stack of a thread. 3. Finalizable - An object which is in a queue awaiting its finalizer to be run.
- 13. How to analyze memory leaks • Find the biggest objects • Analyze why they are kept in memory • Analyze what makes them big
- 14. How the leak analysis was done • Got a “good” heap dump • Found the biggest objects (in the dominator tree) • Analyzed who kept them alive (using paths) • Analyzed what made them big (looking at their retained set) • Used “Leak Report” to automate the analysis
- 15. Inspect the thread to find its activity • Look at the thread attributes - name, class, etc... • Look at the local variables • Look at the stack of the thread
- 16. Find where memory usage can be optimized • Inspect the set of retained objects • Search for inefficiently used data structures • Look for redundant data
- 17. How memory usage was analyzed • Analyzed retained objects (in dominator tree, retained set) • Used “Group by Value” to find redundant objects • Used the commands from the “Collections” group • Used “Component Report” to automate the analysis
- 18. Thank You Resource for slides taken from the following links • http://www.slideshare.net/AJohnson1/practical-lessons-in- memory-analysis# • http://www.slideshare.net/littleeye/memory-analyzer-tool# • http://help.eclipse.org/kepler/index.jsp?topic=/org.eclipse.m at.ui.help/welcome.html