Taming the JVM

Tuning Tools/Techniques

Mike Prasad

..can be adventurous! Or downright grimacing!

Objectives

!   Application challenges

!   JVM Configuration

!   Heap Analysis Tools

!   Future/Alternate Solutions

!   Case Study

Application Challenges

!  Java environment dramatically changed

!  Multi-core, multi-GB environments

!  Understanding JVM important

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

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

Generation Sizing

!  Default values typically used

!  This not always sufficient

!  Requires adjusting generation size

Stack

-Xss set stack size

Heap

-Xms initial heap size

-Xmx maximum heap size

-Xmn young generation heap size

VM Options New Space

-XX:NewSize new gen heap size

-XX:MaxNewSize max new gen heap size

-XX:NewRatio ratio of new/old gen size

-XX:SurvivorRatio eden/survivor space size

Perm Space

-XX:PermSize initial perm size

-XX:MaxPermSize max perm size

-Xnoclassgc eliminates load/unload overhead

Behavioral

-XX:-UseConcMarkSweepGC old gen concurrent mark-sweep

-XX:-UseParallelGC parallel garbage collection

-XX:-UseSerialGC serial garbage collection

Debugging

-XX:-PrintConcurrentLocks Prints concurrent locks

-XX:-PrintGCTimeStamps Print timestamps at gc

-XX:-PrintTenuringDistribution Print tenuring age info

Memory Analysis Tools

!   JMap

!   JConsole

!   Visual GC

!   JRockit Mission Control

!   Others !   JStat

!   HPROF

jmap

!   Prints memory–related statistics

!   Other options !   –heap !   –histo !   -permstat

!  To programmatically monitor use: - java.lang.Runtime.totalMemory()

- java.lang.Runtime.freeMemory()

jmap-heap

Used to obtain :

!   gc name

!   algorithm details !   #threads used for parallel gc

!   heap configuration

!   heap usage summary

jmap -histo

!  Class-wise histogram of the heap

!  Prints out: !  the number of instances !  total amount of memory consumed !  the fully qualified class name

jmap -permstat

!  Get perm gen statistics

!  Configuring perm gen size important

!  Web apps load large number of classes (JPs etc)

!  “too many” classes = OutOfMemoryError

JConsole

!   Monitoring and management tool

!   JMX–compliant attaches to a running JVM

!   JDK 5.0 and above

Visual GC

!   Monitors !   Garbage Collector

!   Compiler

!   Class loader

!   Superior to JConsole

JRockit Mission Control

!   Associated with JRockit JVM

!   Tool Suite : –  visualize gc and other perf stats –  runtime performance profiling tool –  memory-analysis tool

Future !  G1 a new GC in JDK 7

Supports

!  Parallelism : Uses all available CPUs

!  Generational: same as HotSpot GC's

!  Compaction : performs heap compaction

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

Case Study

!  JEE App – Struts/EJB

!  On WebLogic

!  High volume app

!  Overnight performance issues

!  Full GCs every 1.5 minutes

Original VM Settings

-Server

–Xms2048M

–Xmx2048M

–Xmn512M

Attempted # of Settings

-XX:-UseConcMarkSweepGC

-XX:-UseParallelGC

-XX:-UseHailMaryGC (made it worse!)

Problem solved ?

否, いいえ, нет , nein, αριθ. Pizza + Coke = solution

Problem was with the code!

Case Study

Apply rigor – unit test, profile, load test

Moral Of the Story

Don’t look for garbage in the wrong place! Spare the JVM, tame the developer!

Why women live longer!

Finally