This presentation is a basic introduction to MAT. Talks about the basic concepts in Heap Analysis.

1. Eclipse Memory Analyzer
Tool
Lakshman Kakkirala
little eye labs

2. Agenda
● Memory Analysis
● Some Definitions
● An example leak code
● Demo of MAT and some basic functionality

3. Prereqs
● Android app development
● Basic Heap and Garbage Collection
Disqualification
● Advanced knowledge of MAT :-)

4. littleEye appInsight
CT Scanner for your app
http://www.littleeye.co

5. Why Memory Analysis?
● Identify Leaks
● Reduce memory footprint

6. Typical problems
● Holding Context object (an Activity, a View
or a Drawable)
which actually happens to be an Activity
● Non-static inner classes
● Caches
● Aggressive Caching

7. Some definitions
● Shallow Size
● Retained Size
● Dominator
● Dominator Tree
● GCRoots

8. Example - Object Graph
E
B 100
100 100
300
A F
100 100
C 100
600
100
200 D
100
100

9. Example (contd) - Dominator Tree
E
B
F
A
C D

10. Example - Memory Leak
public class MainActivity extends Activity {
private static LeakClass leak;
// *NOT A STATIC*
class LeakClass { }
@Override
public void onCreate(Bundle savedInstanceState) {
....
if (leak == null) {
leak = new LeakClass();
}
...
}
}

11. Investigation Tools - LogCat
● D/dalvikvm( 9050 ): GC_CONCURRENT
freed 2049K, 65% free 3571K/9991K,
external 4703K/5261K, paused 2ms+2ms

12. Heapdump
● What - Snapshot of all the objects in the process
○ Fields, References, Primitive Values
○ Classes, Class Loaders
● How to generate
○ DDMS view - "Dump HPROF file" icon
○ android.os.Debug.dumpHprofData(<filename>)
○ signal 10
● Convert to standard HPROF format
○ hprof-convert (only required if using standalone)

13. MAT aka Eclipse Memory Analyzer
Tool
● Standalone - Download
http://www.eclipse.org/mat
● Pros
○ Visible Primitive Data
○ Powerful selection model
○ No setup
● Cons
○ Large dump files
○ Cannot answer code/temporal questions
■ Who/Where/When - an object is created
■ When - an object is garbage collected

14. Demo
Covering
● View Dominator Tree
● Inspector
○ look at the field values
○ browse through entries in a Collection
● Class Histograms
● Group by Value

15. Demo (contd...)
● Immediate Dominators
● Path from GC roots
● Retained Set
● Object Query Language

16. References
● Google IO 2011 - "Memory Management for Android
apps" http://www.google.
com/events/io/2011/sessions/memory-management-for-
android-apps.html
● Java Memory Analysis
http://vimeo.com/21356498
● Markus Kohler's Java Performance Blog
http://kohlerm.blogspot.com
● Memory Analyzer Blog
http://memoryanalyzer.blogspot.in/

18. Backup Slides
Application Attributes:
<application
android:largeHeap="true">

19. Garbage Collection
Pre Gingerbread:
GC: stop the world gc, >100ms
Gingerbread and beyond:
concurrent gc,
two pauses - at the beginning and at the end
< 5ms
partial collections

20. Bitmap
pre-honeycomb:
● pixel data was stored in native mem
● recycle() or finalize()
● invisible to MAT
honeycomb and after:
● pixel data inside dalvik heap
● visible to MAT
● works with partial and concurrent GC

21. Typical Garbage Collections
GC_CONCURRENT
GC_FOR_MALLOC
GC_EXTERNAL_ALLOC (pre-honeycomb)
GC_HPROF_DUMP_HEAP
GC_EXPLICIT - app calling System.gc()