I need your help: If anyone wants to send me an audio snippet saying "Boring" (as in "Java 26 is stable. It's boring."), I would happily accept them. I want to play this audio via a button press during a talk. In other news: I'm speaking at @amsterdam.voxxeddays.com with @lutskedev.bsky.social.

Java Heap Dumps might contain sensitive information; with hprof-redact, you can easily remove it. Learn more in this blog post: mostlynerdless.de/blog/2026/02...

Command-line parser libraries don't have to be big to support everything you need, like subcommands, validators, and Java-agent-style argument parsing: Introducing femtocli, with a 45KB JAR file. Read more at mostlynerdless.de/blog/2026/02...

Redact sensitive data from Java Flight Recorder and JVM crash logs with jfr-redact, a tool for safely sharing profiling and error files: mostlynerdless.de/blog/2026/02...

Think you really know Java? ☕ Guess the Java version from code snippets in my Java Version Quiz: mostlynerdless.de/java-game/

In this week's blog post, I explain how a chaotic eBPF-based scheduler helps reproduce rare concurrency bugs, illustrated with a real-world OpenJDK case: mostlynerdless.de/blog/2026/01...

A tiny puzzler: Is this valid Java? import java.util.function.Predicate; public class Test { Predicate<String> f = (var a) -> a.isEmpty(); }

I'm looking for suggestions for modern open-source Java applications and libraries for a code analysis project

Async-profiler has released an update that includes native lock profiling and a latency filter. Consequently, ap-loader, which wraps async-profiler in a platform-independent JAR, has also been updated: github.com/jvm-profilin...

JFR is great, but do you know how to read and write JFR files programmatically? Learn more in this week's blog post: mostlynerdless.de/blog/2026/01...

I just released a new version of the cf-cli-java-plugin (github.com/SAP/cf-cli-j...), which solves a rare ssh connection issue by not using the plugin framework to call "cf ssh", but calling it directly via exec.Command

I have just released version 4.2.1-11 of ap-loader, which combines the 4.2.1 async-profiler maintenance release with a bug fix related to --jfr-sync in ap-loader itself. Get it via Maven or from the GitHub releases: github.com/jvm-profilin...

It will probably be one of the most in-depth views into how a feature turned from idea to code in four years. With all the ups and downs.

Java 25 got a new CPU time profiler, get into the details and the journey to get there in my talk at @jfokus.se early February: jfokus.se

After last week's blog post that showed you how OpenJDK is faster than GraalVM, this week you will learn the quickest way to obtain the version of a Java binary (hint: it runs in less than a millisecond): mostlynerdless.de/blog/2026/01...

OpenJDK is faster than GraalVM* It's around twice as fast in one particular area. Read more in my latest tiny blog post at mostlynerdless.de/blog/2026/01...

Discover how to create executables from JAR files using the new execjar project, taking advantage of the fact that JARs are simply ZIP files, in this week's blog post: mostlynerdless.de/blog/2026/01...

I'm happy that so many people find this helpful tool. I've just released a new version that improves performance and allows you to specify JVMs by part of their name, such as `jstall status plexus` to get the status of all running Maven instances.

I hope I'm not the only one who sometimes wonders: "What is my Java application doing right now?" When you don't see any output. This is where my tiny tool called JStall comes in, as you can read in my blog post at mostlynerdless.de/blog/2025/12...

In this week's blog post, you'll learn that JFR doesn't like arrays in other complex types as fields in custom JFR events, and what types are supported: mostlynerdless.de/blog/2025/12...

Discover how to create a Gridfinity chocolate advent calendar and chocolate QR codes in this week's brief blog post: mostlynerdless.de/blog/2025/12...

I'm happy to announce that my meta-agent (a Java agent that instruments other Java agents) now has a nicer Web UI (thanks @hardcoding.fr): github.com/parttimenerd...

In this week's blog post, I'll showcase how the meta-agent hot-patches the JVM to record the byte-code transformations of native Java agents: mostlynerdless.de/blog/2025/11...

Having a last name that comes early when sorted alphabetically sometimes has its advantages:

The JFR events collection website has a new home: sap.github.io/jfrevents Old links will still work and are forwarded to this location.

Running local AI models on Android is easy. In this week's blog post, I showcase my AI server app, which exposes LLMs to Termux and other apps: mostlynerdless.de/blog/2025/11...

I just released the newest version of ap-loader, a platform-independent async-profiler wrapper, which is now built on top of async-profiler 4.2: github.com/jvm-profilin...

Learn how to import JFR data into DuckDB, to easily query and analyze your profiling data in this week's blog post: mostlynerdless.de/blog/2025/10...

Learn how to compare objects from JFR recordings in Java and why this is slightly trickier than you might have expected in this week's blog post: mostlynerdless.de/blog/2025/10...

Learn how to silence the JFR startup messages and why you see them even with the default warning logging level in this week's blog post: mostlynerdless.de/blog/2025/09...

💪 Monday motivation: We are officially one month away from #P99CONF. eBPF has always been a popular topic, and this year is no exception. Don't miss @tanelpoder.com, @ddelnano.bsky.social, Jake Hillion, and @mostlynerdless.de on October 22-23: www.p99conf.io?latest_sfdc_... #ScyllaDB

Learn seven different ways to waste a specific amount of CPU-time in this week's blog post. Number seven will surprise you: mostlynerdless.de/blog/2025/09...

With Java 25, there is finally a CPU-time profiler in the OpenJDK. You can read more about this new profiler and some implementation details in my blog series starting with mostlynerdless.de/blog/2025/06... #java25

Learn how to profile Java applications in Cloud Foundry using the CF CLI Java plugin with SapMachine in my latest blog post: mostlynerdless.de/blog/2025/09...

Learn about the redundant synchronisation in the request queue of Java 25's new CPU time sampler and what we do about it in this week's blog post: mostlynerdless.de/blog/2025/09... P.S.: It also answers the really important question of whether the sampler queue is even a queue.

I just released a new version of my IntelliJ profiler plugin with support for the newest IntelliJ version and the newest async-profiler: plugins.jetbrains.com/plugin/20937...

Queue sizing is hard. Learn all about the sizing of the sampling queues in JDK 25's new CPU-time profiler in my latest blog post at mostlynerdless.de/blog/2025/08...

Sneak peek into my upcoming blog post:

To get you ready for @mostlynerdless.de and @jakehillion.me’s #P99CONF technical session on the Linux scheduler, we're sharing a deep dive from Johannes' hello-ebpf series that looks at concurrency testing using Custom Linux schedulers. www.p99conf.io/2025/08/06/h... #ScyllaDB

Seems like I won't be part of the great Devoxx Belgium conference this year.

TIL: the k3s uninstall script changes the hostname

In this week's blog post, learn how Java 25's new CPU-time profiler works internally, including signal handling, queue design, and async sampling: A deep dive into the core components behind the scenes. Read more at: mostlynerdless.de/blog/2025/07... #Java #OpenJDK #JFR #Profiling

I'm currently working on my blog post on the inner workings of the new JFR CPU-time profiler. But if you want to learn what other ideas I had, you can read my brain-dump ideas list from March 2025 at mostlynerdless.de/blog/2025/07...

I just saw that I published my last blog post more than a month ago. Guess what I'll be working on this week? I procrastinated and had other things to do, so I hope I get into my blogging rhythm again. There are many interesting topics (short and longer) lined up.

I just released ap-loader 4.1 (v10). ap-loader is a wrapper around async-profiler, conveniently packaging all platform versions in one JAR. You can find the newest release on GitHub (github.com/jvm-profilin...) and soon on Maven Central.

Btw. Firefox isn't supporting Java applets for 10 years (blog.mozilla.org/futurereleas...) and Chrome for 11 (blog.chromium.org/2013/09/sayi...), so essentially nobody will notice the removal of applets from Java.

RIP Java Applets. You made Java popular and helped it grow to what it is today. JEP 504: Remove the Applet API has been proposed to target (openjdk.org/jeps/504), so there will be no more applets with the next JDK (JDK 26).

Forget `dd`, `yes >> $HOME/fill_disk.txt` is the best way to reliably fill your disk till the brim. No need to check how much space is left. I used this successfully to test that a tool I'm working on works as expected without disk space left.

TIL: `jcmd $PID GC.heap_dump $FILE` wants the $FILE to either be an absolute location or relative to the current working directory of the Java application (not your current command)