JDK tools for performance
diagnostics
Dror Bereznitsky
Director of Technologies, AlphaCSP

Introduction
Application to slow ?
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2

Introduction
Leaking
Memory
?
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3

Intoduction
Suffering from deadlocks ?
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4

Introduction
The JDK has tools that can help you …
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5

JDK tools for performance diag.
• JDK tools for performance
diagnostics:
 VisualVM  jconsole
 BTrace  jstat
 jhat  jinfo
 jps
 jmap
 jstack
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VisualVM
7

VisualVM
• Java troubleshooting tool
• Visual tool integrating several
command line JDK tools and much
more
• For development and production
time
8

VisualVM Features
• Display local/remote Java
applications
• Monitor memory and threads
• Take and browse heap +
thread dumps
• Extensible with plugins
• Attach API or JMX
9

VisualVM Plugins
• MBean browser
• Visual GC
• Memory sampler
• Profiler – CPU, Memory
• BTrace plugin
• Direct buffers monitor (JDK 7)
• Many more …
10

VisualVM Feature Matrix
JDK 1.4.2 JDK 5 JDK 6 JDK 6
Local Remote
Overview    
System properties 
Monitor    
Threads   
Profiler 
Thread Dump 
Heap Dump 
Heam Dump OOME 
MBean Browser   
JConsole plugins   
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Supported VMs
Java VM Remarks
Sun JDK
Open JDK
Apple JDK
Oracle JRockit
IBM J9 Using JMX only
HP-UX JDK
SAP JDK Requires the VisualVM
Extensions plugin
12

Getting Started
• Version 1.0 ships with JDK6 since
update 7
• Look for jvisualvm in your JDK bin directory
• Version 1.1.1 now ships with JDK6
update 14
• Latest version can be downloaded
from https://visualvm.dev.java.net
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The Demo Application
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VisualVM Demo
VisualVM
Demo
15

Working With Remote Applications
• Start a jstatd daemon on the
remote host
• Allow remote monitoring tools to attach
to running JVMs
• May have security implications
• Add the remote host to the
‘Remote’ node in the Applications
window
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Extending VisualVM
What is VisualVM, really?
Generic desktop application
infrastructure for analyzing sources
of data.
Default data sources
• Applications
• Hosts
• Dumps
• Snapshots
17

Extending VisualVM
• Why you would want to extend
VisualVM:
• Tool-Centric
You have a monitoring or management
tool that you want to make available to
VisualVM
• BTrace plugin
• Application-Centric
You have an application with specific
monitoring/management needs
• Glassfish plugin
18

Extending VisualVM
• What Can You Create?
• Tabs: Main tabs, Sub tabs
• Actions: Menu items, Toolbar
buttons
• Application Types
• Data Sources
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Getting Started With Extending VisualVM
• Install JDK 6
• Read VisualVM API Javadoc &
Tutorials
• Create VisualVM modules
• Netbeans IDE
• VisualVM
samples
collection
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VisualVM Usage Scenarios
• General health monitoring
• Diagnose specific problems
• Memory leaks
• Deadlocks
• Excessive use of finalizers
• Hot lock contention
• Hung process
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BTrace
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BTrace
• Dynamic tracing tool for the Java
platform
• Safe – read, no write
• Low-overhead
• Tracing code is written in Java
• Available as a VisualVM plugin or
as a command line tool
23

Dynamic Tracing
• Works by dynamically
instrumenting classes of a
running Java program – using
ASM 3.0
• ASM is an all purpose Java bytecode
manipulation and analysis framework
• Inserts tracing actions by hot-
swapping the traced program
classes
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BTrace HelloWorld Example
import com.sun.btrace.annotations.*;
import static com.sun.btrace.BTraceUtils.*;
@BTrace
public class HelloWorld {
@OnMethod(
clazz="java.lang.Thread",
method="start"
)
public static void func() {
println("about to start a thread!");
}
}
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BTrace Terminology
• Probe Point
• "location" or "event" at which a set of tracing
statements are executed.
• Trace Actions/Actions
• Trace statements that are executed whenever
a probe "fires".
• Action Methods
• Trace statements that are executed when a
probe fires
• defined inside a static method
• Such methods are called "action" methods.
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BTrace HelloWorld Example
import com.sun.btrace.annotations.*;
import static com.sun.btrace.BTraceUtils.*;
@BTrace
public class HelloWorld {
@OnMethod(
clazz="java.lang.Thread",
method="start" Probe Point
)
public static void func() {
println("about to start a thread!"); Action Method
}
}
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Some BTrace Annotations
• @OnMethod
• Specify target class(es), target
method(s) and "location(s)" within the
method(s)
• @OnLowMemory
• Trace memory threshold exceed event
• @OnTimer
• Specify tracing actions that have to run
periodically once every N milliseconds
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BTrace Restrictions
• can not create new objects.
• can not create new arrays.
• can not throw exceptions.
• can not catch exceptions.
• can not have loops (for, while,
do..while)
• Almost everything is restricted …
29

com.sun.btrace.BTraceUtils
• Contains 270 public static methods
which may be called from a
BTrace script
• Many useful methods:
• deadlocks - prints the Java level
deadlocks detected (if any)
• dumpHeap - dump the snapshot of the
Java heap
• jstack - Prints the java stack trace of
the current thread
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Getting Started
• BTrace is available as a VisualVM
plugin
• Requires VisualVM 1.0.1+
• Available at the BTrace plugin center -
https://btrace.dev.java.net/uc/updates.xml
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BTrace Demo
Demo
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BTrace Demo Source
@BTrace
public class SizeOfStatusCache {
@OnMethod(
clazz = "com.alphacsp.performance.seminar.twitter.Main",
method = "pollForNewStatuses",
location = @Location(Kind.RETURN))
public static void onNewStatuses(Object obj) {
List statusCache =
(List) get(field(classOf(obj), "statusCache", true), obj);
println(concat("Number of cached statuses: ",
str(size(statusCache))));
}
}
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BTrace Usage Scenarios
• Fine grained performance
analysis
• Runtime profiling and monitoring
• Collecting statistics
• When no graphic user interface
available
34

jhat
jhat
35

jhat
• Java Heap Analysis Tool
• Parses a java heap dump and
launches a web server
• Basic web interface for browsing
the heap dump
• Useful for analyzing memory
leaks
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jhat Features
• View all class instances
• View class classloader
• View all references to an object
• View reference chains from
Rootset
• Use OQL (Object Query
Language) to query heap dumps
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OQL
• SQL-like query language to query
Java heap
• Based on JavaScript expression
language
• Built-in objects and functions
• OQL help is available from the
jhat OQL screen
38

Getting Started
C:jdk1.6.0_13bin>jhat -J-mx512m c:heapdump-
1245057502890.hprof
Reading from c:heapdump-1245057502890.hprof...
Dump file created Mon Jun 15 12:18:22 IDT 2009
Snapshot read, resolving...
Resolving 120908 objects...
Chasing references, expect 24
dots........................
Eliminating duplicate
references........................
Snapshot resolved.
Started HTTP server on port 7000
Server is ready.
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jhat demo
jhat Demo
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jhat Usage Scenarios
• When analyzing large heap
dumps – can use a remote
powerful server
• When you do not have a graphic
user interface
• If you want to perform smart
queries on heap content
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Summary
Summary
42

Summary
• The JDK contains useful
performance diagnostics tools
• These tools can be used for
detecting, analyzing and solving
performance related issues
43

References
• Monitoring and Troubleshooting Java
applications using JDK tools (PDF)
• VisualVM
• VisualVM Sample Collection
• TS-4247 Getting More Out of the Java
VisualVM Tool (PDF)
• btrace
• ASM
• jhat
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Thank You 
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