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Install

(For Java11at least version 1.5 is needed) Download Async Profiler from: https://github.com/jvm-profiling-tools/async-profiler

wget https://github.com/jvm-profiling-tools/async-profiler/releases/download/v1.7.1/async-profiler-1.7.1-linux-x64.tar.gz
mkdir /opt/async-profiler
tar xvzf async-profiler-*-linux-x64.tar.gz -C /opt/async-profiler


 Since Kernel 4.6 the following commands must be executed as root on the system to enable profiling

echo 1 > /proc/sys/kernel/perf_event_paranoid
echo 0 > /proc/sys/kernel/kptr_restrict



Usage


Find the HiveMQ process id (must be user root or user hivemq)

#Java Process ID Tool
jps

#or

#ps with filter for only pid and only processes by user hivemq
ps -u hivemq -o pid=

#or

#always works
ps aux | grep hivemq



Run profiler.sh (-d is the duration of the recording in seconds)

/opt/async-profiler/profiler.sh -d 600 -f /(absolute path)/flamegraph.svg <hivemq process id>

You need to make sure that all async-pofiler files belong to the same user that is running the HiveMQ process and that you start the profiler.sh script as that user.

Quick command (can be run as root, only works if hivemq is the only process running for user `hivemq`)

/opt/async-profiler/profiler.sh -d 600 -f /opt/hivemq/flamegraph.svg `ps -u hivemq -o pid=`


Kubernetes / Docker

As usual, container platforms have some paranoid settings that are read-only. On the up side, we can leverage the fact that HiveMQ is always PID 1 in containers (unless shared namespaces are used in K8s):

Here's an idempotent block you can simply execute to generate a flamegraph in a container:

curl -L https://github.com/jvm-profiling-tools/async-profiler/releases/download/v1.7.1/async-profiler-1.7.1-linux-x64.tar.gz > async.tar.gz
tar xfvz async.tar.gz
rm -f flame.svg
./profiler.sh -d 60 -f $(pwd)/flame.svg 1 --all-user -e alloc

Then use kubectl cp or docker cp to copy the graph from the container.

systemd

Alternative: When using systemd, you can simply use 

systemctl show --property MainPID hivemq | sed -e "s/MainPID=//"


Using async profiler in the systemd unit (start with HiveMQ):

sed -i -e "s|-Djava.net.preferIPv4Stack=true|-Djava.net.preferIPv4Stack=true -agentpath:/opt/async-profiler/build/libasyncProfiler.so=start,svg,file=flamegraph.svg|" /opt/hivemq/bin/run.sh


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