Awesome

jfr-report-tool

Tool for creating reports from Java Flight Recorder dumps.

Influenced by https://github.com/chrishantha/jfr-flame-graph . Kudos to @chrishantha for the great work.

Uses Java Flight Recorder internal API to read JFR dump files.

Uses flamegraph.pl from FlameGraph for creating flamegraphs in SVG format.

Requirements

JAVA_HOME environment variable must point to Oracle JDK 1.7.0_40+.

Usage with provided shell script (requires bash)

./jfr-report-tool [dump_file.jfr]

The script will build the tool on first access using ./gradlew shadowJar command. It will also use curl to download flamegraph.pl if it's not available on PATH.

usage: jfr-report-tool [-abcdefghilmnorsw] [jfrFile]
 -a,--action <action>                   Tool action. Valid choices:
                                        flameGraph, stacks, topframes,
                                        dumpinfo, recordtypes
    --allocations                       Allocation flamegraph
 -b,--begin <seconds>                   Begin time
 -c,--cutoff <pattern>                  Cut off frame pattern
 -d,--duration <seconds>                Duration of time window, splits
                                        output in to multiple files
 -e,--exclude <filter>                  Regexp exclude filter for methods
 -f,--first-split                       First window duration half of
                                        given duration
    --flamegraph-command <cmd>          flamegraph.pl path
 -g,--grep <filter>                     Regexp to include all stacks with
                                        match in any frame
 -h,--help                              Help
 -i,--include <filter>                  Regexp include filter for methods
 -l,--length <seconds>                  Length of selected time
 -m,--min <value>                       Minimum number of samples
    --min-samples-frame-depth <value>   Minimum samples sum taken at frame
                                        depth
 -n,--no-compress                       Don't compress package names
 -o,--output <file>                     Output file
 -r,--reverse                           Process stacks in reverse order
 -s,--sort                              Sort frames
 -w,--width <pixels>                    Width of flamegraph
Supported actions:
flameGraph                       creates flamegraph in svg format, default action
stacks                           creates flamegraph input file
topframes                        shows top methods
dumpinfo                         dump info
recordtypes                      dump record types

Examples

Flamegraph

This creates a file jfr_dump_file.jfr.svg that is the flamegraph in SVG format. SVG files can be opened with most web browsers.

./jfr-report-tool jfr_dump_file.jfr

Disabling default filtering

./jfr-report-tool -e none -m 1 jfr_dump_file.jfr

By default, the tool removes all methods matching ^(java\.|sun\.|com\.sun\.|org\.codehaus\.groovy\.|groovy\.|org\.apache\.) so that you can view hotspots in your own code. Use "-e none" to disable method filtering. By default, all stacks with 1 or 2 samples will be filtered. You can disable this be setting the min parameter to 1.

Allocations flamegraph

To visualize allocations, there is a new feature to render a flamegraph where each stacktrace is weighted with the allocation size made in each method. It uses the JFR java/object_alloc_in_new_TLAB and java/object_alloc_outside_TLAB events to get allocation data. These events are enabled when using settings=profile in FlightRecorderOptions.

See Allocation Profiling in Java Mission Control blog post for explanation of the events.

Note that we, in the case of the (inside) TLAB allocation events, are not emitting an event for each and every location – that would be way too expensive. We are instead creating an event for the first allocation in a new TLAB. This means that we get a sampling of sorts of the thread local allocations taking place.

Since java/object_alloc_in_new_TLAB only capture the first allocation in a new TLAB, the events won't show all allocations. It's possible to pass -XX:-UseTLAB to record all allocations, but this adds a lot of overhead to JFR profiling.

example of visualizing allocations with a flamegraph

./jfr-report-tool --allocations jfr_dump_file.jfr

Java Flight Recorder

Enabling Java Flight Recorder

Add these JVM startup parameters

-XX:+UnlockCommercialFeatures -XX:+FlightRecorder -XX:+UnlockDiagnosticVMOptions -XX:+DebugNonSafepoints -XX:FlightRecorderOptions=stackdepth=1024

Use this FlightRecorderOptions parameter to start recording from the start and create a dump on exit to the current directory:

-XX:FlightRecorderOptions=defaultrecording=true,settings=profile,disk=true,maxsize=500M,stackdepth=1024,dumponexit=true

This uses $JAVA_HOME/jre/lib/jfr/profile.jfc settings which has method sampling enabled.

Controlling Java Flight Recorder at runtime from command line

jcmd is used to control JFR.

Help for all jcmd commands:

jcmd <PID> help

You can use jps to find the process id (PID) of the java process you want to profile.

The available commands are JFR.stop, JFR.start, JFR.dump, JFR.check

Help for JFR.start

jcmd <PID> help JFR.start

Creating a recording by jcmd

starting recording with setting from $JAVA_HOME/jre/lib/jfr/profile.jfc

jcmd <PID> JFR.start name=myrecording settings=profile

dumping to file and continuing recording

jcmd <PID> JFR.dump name=myrecording filename=$PWD/mydump.jfr

Customizing profiling settings

It's recommended to create a custom JFR settings file with highest sampling rate (10ms). profiling.jfc example. You can use the Java Mission Control UI to edit JFR setting files. The feature is called "Java Flight Recording Template Manager".

Controlling Java Flight Recorder at runtime from graphical user interface

Use jmc command to start the Java Mission Control UI. The UI can be used to do recordings.