JDK tools for performance diagnostics

Dror BereznitskyDirector of Technologies, AlphaCSP

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Introduction

Application to slow ?

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Introduction

Leaking

Memory

?

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Intoduction

Suffering from deadlocks ?

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Introduction

The JDK has tools that can help you …

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JDK tools for performance diag.

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• JDK tools for performance diagnostics:

VisualVM

BTrace

jhat jmap

jconsole

jstat

jinfo

jps

jstack

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VisualVM

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VisualVM

• Java troubleshooting tool

• Visual tool integrating several command line JDK tools and much more

• For development and production time

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VisualVM Features

• Display local/remote Java applications

• Monitor memory and threads

• Take and browse heap + thread dumps

• Extensible with plugins

• Attach API or JMX

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• MBean browser

• Visual GC

• Memory sampler

• Profiler – CPU, Memory

• BTrace plugin

• Direct buffers monitor (JDK 7)

• Many more …

VisualVM Plugins

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VisualVM Feature Matrix

JDK 6

Remote

JDK 6

Local

JDK 5JDK 1.4.2

Overview

System properties

Monitor

Threads

Profiler

Thread Dump

Heap Dump

Heam Dump OOME

MBean Browser

JConsole plugins

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Supported VMs

RemarksJava VM

Sun JDK

Open JDK

Apple JDK

Oracle JRockit

Using JMX onlyIBM J9

HP-UX JDK

Requires the VisualVM Extensions plugin

SAP JDK

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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

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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

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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

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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

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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"

)

public static void func() {

println("about to start a thread!");

}

}

Probe Point

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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• 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 …

BTrace Restrictions

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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

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jhat

jhat

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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

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Getting Started

C:\jdk1.6.0_13\bin>jhat -J-mx512m c:\heapdump-1245057502890.hprof

Reading from c:\heapdump-1245057502890.hprof...Dump file created Mon Jun 15 12:18:22 IDT 2009Snapshot read, resolving...Resolving 120908 objects...Chasing references, expect 24

dots........................Eliminating duplicate

references........................Snapshot resolved.Started HTTP server on port 7000Server 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

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Summary

• The JDK contains useful performance diagnostics tools

• These tools can be used for detecting, analyzing and solving performance related issues

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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