Troubleshooting Tools In JDK
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The document discusses various monitoring and troubleshooting tools available in the JDK 'bin' folder. It summarizes the key tools like jconsole for monitoring Java applications, jcmd for sending diagnostic commands, jmap for creating heap dumps, and jstack for thread stack traces. It also discusses tools that have been removed from newer JDK versions like Java VisualVM and jhat.
![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
Copyright © 2019 Oracle and/or its affiliates.](https://image.slidesharecdn.com/troubleshootingtoolsinjdk-190920040919/85/Troubleshooting-Tools-In-JDK-15-320.jpg)
![$ 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
Copyright © 2019 Oracle and/or its affiliates.](https://image.slidesharecdn.com/troubleshootingtoolsinjdk-190920040919/85/Troubleshooting-Tools-In-JDK-16-320.jpg)
![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>]
Copyright © 2019 Oracle and/or its affiliates.](https://image.slidesharecdn.com/troubleshootingtoolsinjdk-190920040919/85/Troubleshooting-Tools-In-JDK-17-320.jpg)
![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
Copyright © 2019 Oracle and/or its affiliates.](https://image.slidesharecdn.com/troubleshootingtoolsinjdk-190920040919/85/Troubleshooting-Tools-In-JDK-33-320.jpg)
![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]
Copyright © 2019 Oracle and/or its affiliates.](https://image.slidesharecdn.com/troubleshootingtoolsinjdk-190920040919/85/Troubleshooting-Tools-In-JDK-36-320.jpg)
Troubleshooting Tools In JDK
- 1. 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
- 2. 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 prospects are “forward-looking statements” and are subject to material risks and uncertainties. A detailed discussion of these factors and other risks that affect our business is contained in Oracle’s Securities and Exchange Commission (SEC) filings, including our most recent reports on Form 10-K and Form 10-Q under the heading “Risk Factors.” These filings are available on the SEC’s website or on Oracle’s website 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 Copyright © 2019 Oracle and/or its affiliates.
- 3. 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! Copyright © 2019 Oracle and/or its affiliates.
- 4. 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 Copyright © 2019 Oracle and/or its affiliates.
- 5. Agenda • Tools available in JDK ‘bin’ folder • Monitoring Tools • Troubleshooting Tools • Newly Added Tools • Decommissioned Tools Copyright © 2019 Oracle and/or its affiliates.
- 6. 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 Copyright © 2019 Oracle and/or its affiliates.
- 7. 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 Copyright © 2019 Oracle and/or its affiliates.
- 8. Java Application JMX Client Application Instrumented JVM JMX Agent MBean Server MBean MBean MBean Copyright © 2019 Oracle and/or its affiliates.
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- 15. 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 Copyright © 2019 Oracle and/or its affiliates.
- 16. $ 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 Copyright © 2019 Oracle and/or its affiliates.
- 17. 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>] Copyright © 2019 Oracle and/or its affiliates.
- 18. 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 Copyright © 2019 Oracle and/or its affiliates.
- 19. 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. Copyright © 2019 Oracle and/or its affiliates.
- 20. 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 Copyright © 2019 Oracle and/or its affiliates.
- 21. 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 Copyright © 2019 Oracle and/or its affiliates.
- 22. 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 Copyright © 2019 Oracle and/or its affiliates.
- 23. 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 Copyright © 2019 Oracle and/or its affiliates.
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- 28. Copyright © 2019 Oracle and/or its affiliates.
- 29. jcmd Attach API Diagnostic Routines Commands Output Local machine Copyright © 2019 Oracle and/or its affiliates.
- 30. 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 Copyright © 2019 Oracle and/or its affiliates.
- 31. jinfo jmap jstack Local live process Core dump file Remote Debug ServerJDK 8 JDK 9+ Serviceability Agent Attach API Copyright © 2019 Oracle and/or its affiliates.
- 32. 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 Copyright © 2019 Oracle and/or its affiliates.
- 33. 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 Copyright © 2019 Oracle and/or its affiliates.
- 34. jstack (experimental) – Java Stack • Thread dump • Deadlock detection • jstack –l to see the concurrent locks information • Removed support for –F and –m options Copyright © 2019 Oracle and/or its affiliates.
- 35. 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 Copyright © 2019 Oracle and/or its affiliates.
- 36. 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] Copyright © 2019 Oracle and/or its affiliates.
- 37. jinfo jmap jstack Local live process Core dump file Remote Debug Server JDK 9+ Serviceability Agent Attach API Copyright © 2019 Oracle and/or its affiliates.
- 38. jhsdb Local live process Core dump file Remote Debug Server JDK 9+ Serviceability Agent Non-cooperative manner Copyright © 2019 Oracle and/or its affiliates.
- 39. Copyright © 2019 Oracle and/or its affiliates.
- 40. Copyright © 2019 Oracle and/or its affiliates.
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- 46. Copyright © 2019 Oracle and/or its affiliates.
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- 48. Copyright © 2019 Oracle and/or its affiliates.
- 49. 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 Copyright © 2019 Oracle and/or its affiliates.
- 50. Copyright © 2019 Oracle and/or its affiliates.
- 51. 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 Copyright © 2019 Oracle and/or its affiliates.
- 52. 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 Copyright © 2019 Oracle and/or its affiliates.
- 53. Tools Removed in JDKs • JDK 9 • Java VisualVM • jhat • jsadebugd • JDK 11 • jmc Copyright © 2019 Oracle and/or its affiliates.
- 54. 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 Copyright © 2019 Oracle and/or its affiliates.
- 55. 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 Copyright © 2019 Oracle and/or its affiliates.
- 56. 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’ Copyright © 2019 Oracle and/or its affiliates.
- 57. 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 Copyright © 2019 Oracle and/or its affiliates.
- 58. Copyright © 2019 Oracle and/or its affiliates.
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- 60. Copyright © 2019 Oracle and/or its affiliates.
- 61. Copyright © 2019 Oracle and/or its affiliates.
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- 64. Copyright © 2019 Oracle and/or its affiliates.
- 65. Copyright © 2019 Oracle and/or its affiliates.
- 66. Copyright © 2019 Oracle and/or its affiliates.
- 67. 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) Copyright © 2019 Oracle and/or its affiliates.
- 68. 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 Copyright © 2019 Oracle and/or its affiliates.
- 69. 69 Monitoring and Troubleshooting Tools in JDK ‘bin’ Poonam Parhar Consulting Member of Technical Staff JVM Sustaining Engineer, Oracle Copyright © 2019 Oracle and/or its affiliates.