Practical Lessons in Memory Analysis

Transcription

1 Practical Lessons in Memory Analysis Krum Tsvetkov SAP AG Andrew Johnson IBM United Kingdom Limited

2 GOAL > Learn practical tips and tricks for the analysis of common memory-related problems 2

3 Agenda > Introduction > Analyzing Memory Leaks > Analyzing a Heavy Request > Reducing Memory Footprint > Non-heap Memory > Summary > Q & A 3

4 Why Care about Memory? > Memory is a crucial resource > Excessive memory usage can cause: Crashes in the application Unresponsive applications Unpredictable program behavior > Memory analysis is complicated 4

5 How Will This Session Help Me? > Present common memory-related issues > Give hints how to solve them using heap dumps and Memory Analyzer > Show many demos using real-life heap dumps > Show how to simplify analysis by automating it 5

6 Heap Dumps Are Useful for Analysis > Heap dumps come for free > They are suitable for production > The comprehensive data allows detailed analysis > There is a wide platform coverage HPROF dumps from HotSpot based JVMs DTFJ and PHD dumps from IBM JVMs 6

7 Agenda > Introduction > Analyzing Memory Leaks > Analyzing a Heavy Request > Reducing Memory Footprint > Non-heap Memory > Summary > Q & A 7

8 First, Collect Data For Analysis > Enable heap dumps on OutOfMemoryError > Trigger heap dumps on demand if needed > How-to for getting a heap dump: 8

9 How to Get a Good Heap Dump? Max Heap Min Heap Processing Space Base Memory > When memory is exhausted the leak will occupy most of the processing space > Ensure big enough processing space, this will make the leak easier to find 9

10 How to Analyze Memory Leaks > Find the biggest objects > Analyze why they are kept in memory > Analyze what makes them big 10

11 DEMO > Analysis of a Memory Leak 11

12 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 12

13 Agenda > Introduction > Analyzing Memory Leaks > Analyzing a Heavy Request > Reducing Memory Footprint > Non-heap Memory > Summary > Q & A 13

14 What Is a Heavy Request? > An expensive operation which can cause an OutOfMemoryError > Acute rather than a chronic problem > Examples: Reading a big file in memory not in chunks Try to load a whole DB table in memory 14

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 15

16 DEMO > Analysis of a Heavy Request 16

17 How Thread Activity Was Analyzed > Inspected thread attributes and local variables (in object explorer) > Analyzed stack trace 17

18 Agenda > Introduction > Analyzing Memory Leaks > Analyzing a Heavy Request > Reducing Memory Footprint > Non-heap Memory > Summary > Q & A 18

19 Why is Memory Footprint Important? Max Heap Min Heap Processing Space Base Memory > A lower memory footprint can improve: The scaling of an application / server Performance by increasing the time between GCs 19

20 Find Where Footprint Can Be Optimized > Inspect the set of retained objects > Search for inefficiently used data structures > Look for redundant data 20

21 DEMO > Analysis of High Memory Footprint 21

22 How Memory Footprint 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 22

23 Agenda > Introduction > Analyzing Memory Leaks > Analyzing a Heavy Request > Reducing Memory Footprint > Non-heap Memory > Summary > Q & A 23

24 Non-heap Memory Can Be Exhausted > What is in the non-heap memory? Metadata for classes Interned Strings (for some JVMs) > How can it be exhausted? Too many interned Strings Classes packaged and loaded multiple times Class loaders which are not properly released 24

25 Why Is a Class Loader Not Released? > The trivial case there is a normal reference to it > A common case it is the context class loader of a thread > The registry problem one instance is enough 25

26 How to Analyze Leaking Class Loaders > Find classes loaded more than once > Find redundant loaders by their name > Look at the paths to the suspect class loaders 26

27 DEMO > Analyzing Leaking Class Loaders 27

28 How Was the Leaking Class Loaders Analysis Done > Used the Duplicate Classes query > Found the loaders that load redundant classes > Analyzed why they are not released (using paths) 28

29 Agenda > Introduction > Analyzing Memory Leaks > Analyzing a Heavy Request > Reducing Memory Footprint > Non-heap Memory > Summary > Q & A 29

30 Summary > Heap dumps are very helpful for memory analysis > Memory Analyzer offers rich analysis feature set > The analysis can often be automated 30

31 Questions and Answers > Memory Analyzer Eclipse 31

32 Krum Tsvetkov Andrew Johnson 32