Troubleshooting Tools In JDK

1
Monitoring and Troubleshooting
Tools in JDK ‘bin’
Poonam Parhar
Copyright © 2019 Oracle and/or its affiliates.
Consulting Member of Technical Staff
JVM Sustaining Engineer, Oracle

The following is intended to outline our general product direction. It is intended for information purposes
only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code,
or functionality, and should not be relied upon in making purchasing decisions. The development,
release, timing, and pricing of any features or functionality described for Oracle’s products may change
and remains at the sole discretion of Oracle Corporation.
Statements in this presentation relating to Oracle’s future plans, expectations, beliefs, intentions and
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at http://www.oracle.com/investor. All information in this presentation is current as of September 2019
and Oracle undertakes no duty to update any statement in light of new information or future events.
Safe Harbor

What is Troubleshooting ?
• Systematic approach to solving problems
• Three simple steps:
• 1. Understand the problem/error
• 2. Collect the required diagnostic data
• 3. Analyze the collected data
Good Troubleshooting tools are our friends!

JDK Troubleshooting/Monitoring Tools
• Tools that allow us to
• Monitor Java applications
• Profile Java applications
• Extract useful diagnostic information from Java applications
• Analyze diagnostic data
• Even perform after-the-fact analysis
• Can work locally or remotely

Agenda
• Tools available in JDK ‘bin’ folder
• Monitoring Tools
• Troubleshooting Tools
• Newly Added Tools
• Decommissioned Tools

Monitoring Tools
• jconsole - Starts a graphic console to monitor and manage Java
applications.
• jps - Experimental: Lists the instrumented Java Virtual
Machines (JVMs) on the target system.
• jstat - Experimental: Monitors JVM statistics
• jstatd - Experimental: Monitors JVMs and enables remote
monitoring tools to attach to JVMs.
• jmc – Java Mission Control: JMX console, and JFR recording
and analysis tool
Open
sourced
and is not
shipped
with
Oracle JDK

JConsole
• JConsole is a GUI based monitoring tool for Java applications
• JMX client
• Helps in monitoring and managing
• Java Applications and the JVM
• Local and remote applications
• jconsole executable available in JDK/bin
• Using jConsole locally is not recommended for production
environments
• For remote monitoring:
• com.sun.management.jmxremote.port=portNum

Java Application
JMX Client
Application
Instrumented JVM
JMX Agent
MBean
Server
MBean
MBean
MBean

jps (experimental) – Java Process Status
tool
• Lists the JVMs running on the system
• Obtains processes information from /tmp/hsperfdata_user/<pid>
files
• List of the JVMs reported can be limited by the OS level permissions
granted to the user
• Can list the JVMs on local or remote hosts
• For remote monitoring ‘jstatd’ should be running on the remote
system
• Accepts optional argument <protocol:><//hostname>:[<port>]
• On local hosts, the VM identifier is typically the OS process id of the
application

$ jps -h
illegal argument: -h
usage: jps [-help]
jps [-q] [-mlvV] [<hostid>]
Definitions:
<hostid>: <hostname>[:<port>]
$ jps -m
9848 GCBasher.jar -time:100000000
7084 Jps –m
$ jps -l
3056 jdk.jcmd/sun.tools.jps.Jps
9848 GCBasher.jar
$ jps -v
6324 Jps -Dapplication.home=d:Javajdk-9 -Xms8m -Djdk.module.main=jdk.jcmd
9848 GCBasher.jar
C:Userspobajaj.ORADEV>jps -q
9876
9848
jps examples

jstat (experimental) – JVM Statistics
• Tool to monitor JVM statistics
• Performance statistics about HotSpot JVM
• Reads information from /tmp/hsperfdata_user/<pid> file
• Accepts various options to print statistics about different
components of the JVM
• class, compiler, gc, gccapacity, gccause, gcnew, gcnewcapacity, gcold,
gcoldcapacity, gcmetacapacity, gcutil, printcompilation
• For remote monitoring ‘jstatd’ must be running on the remote
system
• Accepts optional argument <protocol:><//hostname>:[<port>]

jstatd (experimental) - jstat Daemon
• Launches an RMI server application that monitors the creation
and termination of HotSpot JVM based java applications
• Provides an interface to allow remote monitoring tools to attach
to Java virtual machines running on the system
• Note: There is no encryption or authentication with jstatd

Monitoring Tools
• jconsole - Starts a graphic console to monitor and manage Java
applications.
• jps - Experimental: Lists the instrumented Java Virtual Machines
(JVMs) on the target system.
• jstat - Experimental: Monitors JVM statistics
• jstatd - Experimental: Monitors JVMs and enables remote
monitoring tools to attach to JVMs.

Troubleshooting Tools
• jcmd – Sends diagnostic commands to a running JVM
• jdb – java platform debugger
• jinfo – Experimental: Obtains and updates configuration information
• jmap – Experimental: Can create heap dumps or heap histograms for
a java process
• jstack – Experimental: Prints Java thread stack traces for a Java
process
• jhsdb – Attaches to a hanging process or a crash dump file for
postmortem analysis
• jfr – command line tool to analyze JFR recording files
New
tool
in
JDK
9
New
diagnostic
commands
New tool in JDK
12

jcmd – Java Command
• Java Diagnostic Command utility
• Utility to send diagnostic commands to a running JVM
• Uses Attach API to execute d-commands (helper routines) in
the JVM
• Can be used only on the same local machine as the target JVM

jcmd: popular commands
• jcmd <process id/main class> VM.version
• jcmd <process id/main class> VM.system_properties
• jcmd <process id/main class> VM.flags
• jcmd <process id/main class> GC.class_histogram
• jcmd <process id/main class> GC.class_stats
• jcmd <process id/main class> GC.heap_dump
filename=heapdump
• jcmd <process id/main class> Thread.print

jcmd: Java Flight Recordings commands
• jcmd <process id/main class> JFR.start name=MyRecording
settings=profile delay=20s duration=2m
filename=/tmp/myrecording.jfr
• jcmd <process id/main class> JFR.check
• jcmd <process id/main class> JFR.stop
• jcmd <process id/main class> JFR.dump name=MyRecording
filename=/tmp/myrecording.jfr

jcmd Attach API
Diagnostic
Routines
Commands
Output
Local
machine

jdb – Java Debugger
• Command-line debugger for Java Class files
• jdb <options> <class> <arguments>
• Uses Java Debug Interface (JDI)
• JDI is a component of Java Platform Debugger Architecture
(JPDA)
• Can perform inspection and debugging of a local or remote
Java Virtual Machine

jinfo
jmap
jstack
Local live process
Core dump file
Remote Debug ServerJDK 8
JDK
9+
Serviceability Agent
Attach API

jinfo – Java Configuration Information
• Configuration (flags) information of a running Java process
• Can update the manageable flags at runtime
• It can:
• Print the value of a VM flag
• Enable or disable a specified VM flag
• Set the value of a VM flag
• Print VM flags and system properties

jmap (experimental) – Java Memory Map
• Heap objects information and Heap dumps
• Classloader Statistics
• -clstats <pid>
• Finalization Information
• -finalizerinfo <pid>
• Class Histograms
• -histo[:live] <pid>
• Heap Dumps
• -dump:<dump-options> <pid>
• JDK 9 removed: heap info and shared memory mappings

jstack (experimental) – Java Stack
• Thread dump
• Deadlock detection
• jstack –l to see the concurrent locks information
• Removed support for –F and –m options

jcmd – comparison with old tools
jcmd Individual tools Function
jcmd without any argument jps List Java Processes
jcmd with VM.system_properties, VM.flags, VM.set_flag jinfo VM Configuration
jcmd with GC.class_stats, GC.class_histogram,
GC.heap_dump, GC.finalizer_info
jmap Generate Heap Dump
and Class Histogram, get
Class Statistics and
Finalization information
jcmd with Thread.print jstack Thread Dump
jcmd PerfCounter.print jstat Print Performance
Counters

jhsdb- Java HotSpot Debugger
• Can be used to launch a postmortem debugger (SA) to analyze
core dump files
• Can be used for live java processes too
• jhsdb clhsdb [--pid pid | --exe executable --core coredump]
• jhsdb debugd [options] pid [server-id]|[option] executable core [server-id]
• jhsdb hsdb [--pid pid | --exe executable --core coredump]
• jhsdb jstack [--pid pid | --exe executable --core coredump] [options]
• jhsdb jmap [--pid pid | --exe executable --core coredump] [options]
• jhsdb jinfo [--pid pid | --exe executable --core coredump] [options]
• jhsdb jsnap [options] [--pid pid | --exe executable --core coredump]

jinfo
jmap
jstack
Local live process
Core dump file
Remote Debug Server
JDK
9+
Attach API

jhsdb
Local live process
Core dump file
Remote Debug Server
JDK
9+
Non-cooperative manner

JFR Tool
• Where GUI tools (e.g. JMC) can not be used
• https://bugs.openjdk.java.net/browse/JDK-8205516
• Available since JDK 12
• Will also be available in 11.0.6 Oracle JDK

JFR Tool Commands
jfr print recording.jfr
jfr print --events CPULoad,GarbageCollection recording.jfr
jfr print --json --events CPULoad recording.jfr
jfr print --categories "GC,JVM,Java*" recording.jfr
jfr print --events "jdk.*" --stack-depth 64 recording.jfr
jfr summary recording.jfr
jfr metadata recording.jfr

Troubleshooting Tools
• jcmd – Sends diagnostic commands to a running JVM
• jdb – java platform debugger
• jinfo – Experimental: Generates configuration information
• jmap – Experimental: Can create heap dumps or heap
histograms for a java process
• jstack – Experimental: Prints Java thread stack traces for a Java
process
• jhsdb – Attaches to a hanging process or a crash dump file for
postmortem analysis
• jfr – command line tool to analyze JFR recording files

Tools Removed in JDKs
• JDK 9
• Java VisualVM
• jhat
• jsadebugd
• JDK 11
• jmc

Java VisualVM
• Not included since JDK 9
• Open Source Project: https://visualvm.github.io/download.html
• Other tools (profiling and live monitoring) available: Java
Mission Control, JConsole
• Several Open Source heap dumps analysis tools available
• Eclipse MAT

jhat
• Removed in JDK 9
• Web application that can be launched with the ‘jhat’ command
available in the JDK/bin folder
• Enables heap dump analysis by browsing objects in the heap
dump using any web browser
• By default the web server is started at port 7000.
• jhat supports a wide range of pre-designed queries and Object
Query Language(OQL) to explore the objects in heap dumps
• Several other heap dump analysis tools available

jsadebugd
• Removed in Java 9
• Attaches to a Java process or core file and acts as a debug
server
• Up until JDK 8, tools such as jstack, jmap, and jinfo could
remotely attach to a debug server using Java RMI
• The debug server can now be launched with ‘jhsdb debugd’

JMC - Java Mission Control
• Open Sourced: http://hg.openjdk.java.net/jmc
• Building JMC: http://hirt.se/blog/?p=947
• Not available in ‘bin’ since JDK 11
• Non-intrusive, low-overhead tool to monitor, manage and profile Java
applications
• Suitable for production environments
• JMC Tools Chain
• JMX Console
• Monitoring and managing live java applications
• JMX MBeans Browser
• Java Flight Recorder
• Engine built in the Java Runtime
• Record interesting events at the application and the JVM level
• Compact binary proprietary format
• Tracking events leading up to a problem provides great help in troubleshooting

Update on JFR
• JEP 328: Flight Recorder
• JFR open sourced in JDK 11
• Was a commercial feature earlier, and needed commercial license and -
XX:+UnlockCommercialFeatures option
• Flight Recorder API
• Added in JDK 9
• Old Object Sample Event (Memory Leak Profiler)
• Added in JDK 10
• Marcus’s blog post: http://hirt.se/blog/?p=1055
• Performance enhancements in data collection and recording
• Ability to dump recordings even at VM crashes or OOMs
• Improved and new Events (safepoint, codecache, compiler, G1, module)

Summary
• Enhanced Tools
• jcmd – we encourage to use this tool instead of other individual tools
• New Tools
• jfr tool
• jhsdb for postmortem analysis
• Removed Tools
• Java VisualVM
• jhat
• jsadebugd
• jmc

69
Monitoring and Troubleshooting
Tools in JDK ‘bin’
Poonam Parhar
Consulting Member of Technical Staff
JVM Sustaining Engineer, Oracle

Troubleshooting Tools In JDK

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