Mike Prasad's IGNITE presentation at DOSUG about tuning the JVM parameters for optimal performance.

1. Taming the
JVM
Tuning Tools/Techniques
Mike Prasad
Or downright grimacing!
..can be adventurous!

2. Objectives
! Application challenges
! JVM Configuration
! Heap Analysis Tools
! Future/Alternate Solutions
! Case Study

3. Application Challenges
! Java environment dramatically
changed
! Multi-core, multi-GB environments
! Understanding JVM important

4. Java Memory
! Divided into two areas – Stack & Heap
Stack
! associated with methods
! intermediate calcs
Heap
! All objects created using “new” keyword
! GC responsible for cleaning dead/unwanted objects
! Heap sizes controlled by command line options

5. Java Garbage Collector
! Objects either in young or tenured generations
! Minor GC when young objects die
! Surviving objects moved to tenured gen
! Full GC when tenured gen needs to be collected
http://java.sun.com/docs/hotspot/gc5.0/gc_tuning_5.html

6. Generation Sizing
! Default values typically used
! This not always sufficient
! Requires adjusting generation
size

7. VM Options
New Space
Behavioral
Stack
-XX:NewSize
-XX:-UseConcMarkSweepGC new gen heap size
old gen concurrent mark-sweep
-Xss
-XX:MaxNewSize
-XX:-UseParallelGC size
set stack parallel garbage collection
max new gen heap size
-XX:-UseSerialGC serial garbage collection
-XX:NewRatio ratio of new/old gen size
-XX:SurvivorRatio eden/survivor space size
Heap
Debugging -Xms initial heap size
Perm Space
-XX:-PrintConcurrentLocks
-Xmx maximum heap size
Prints concurrent locks
-XX:PermSize initial perm size
-XX:-PrintGCTimeStamps Print timestamps at gc
-Xmn
-XX:MaxPermSize max perm generation heap size
-XX:-PrintTenuringDistributionyoung size
Print tenuring age info
-Xnoclassgc eliminates load/unload overhead

8. Memory Analysis Tools
! JMap
! JConsole
! Visual GC
! JRockit Mission Control
! Others
! JStat
! HPROF

9. jmap
! Prints memory–related statistics
! Other options
! –heap
! –histo
! -permstat
! To programmatically monitor use:
- java.lang.Runtime.totalMemory()
- java.lang.Runtime.freeMemory()

10. jmap-heap
Used to obtain :
! gc name
! algorithm details
! #threads used for parallel gc
! heap configuration
! heap usage summary

11. jmap -histo
! Class-wise histogram of the heap
! Prints out:
! the number of instances
! total amount of memory consumed
! the fully qualified class name

12. jmap -permstat
! Get perm gen statistics
! Configuring perm gen size important
! Web apps load large number of classes
(JPs etc)
! “too many” classes = OutOfMemoryError

13. JConsole
! Monitoring and management tool
! JMX–compliant attaches to a running JVM
! JDK 5.0 and above

14. Visual GC
! Monitors
! Garbage Collector
! Compiler
! Class loader
! Superior to JConsole

15. JRockit Mission Control
! Associated with JRockit JVM
! Tool Suite :
– visualize gc and other perf stats
– runtime performance profiling tool
– memory-analysis tool

16. Future
! G1 a new GC in JDK 7
Supports
! Parallelism : Uses all available CPUs
! Generational: same as HotSpot GC's
! Compaction : performs heap compaction

17. Appliance Solution
! Theoretical heap limit of 32-bit JVM is 4G
! Azul appliance provides
! hardware-assisted pauseless gc feature
! Up to 864 cores with 768GB heap!
! Xfer workload from app server to appliance

18. Case Study
! JEE App – Struts/EJB
! On WebLogic
! High volume app
! Overnight performance issues
! Full GCs every 1.5 minutes

19. Case Study
Original VM Settings
Attempted # of Settings
-Server
-XX:-UseConcMarkSweepGC
–Xms2048M
ProblemPizza + ?
solved Coke = solution
-XX:-UseParallelGC
–Xmx2048M
, , нет , nein, αριθ.
-XX:-UseHailMaryGC (made it
–Xmn512M worse!)
Problem was with the code!

20. Moral FinallyStory
Of the
Apply rigor forJVM, test, the developer! test
Don’t lookthe unit tamein the wrong place!
Spare – garbage profile, load
Why women live longer!