What Options a HotSpot JVM Supports?

Today, I've taken notice of two helpful HotSpot JVM options: -XX:+PrintFlagsInitial and -XX:+PrintFlagsFinal. The first one shows the initial HotSpot options and their values, before HotSpot applies its rules and optimizations; the second one shows them afterwards. Comparing these two might help you to understand, how the HotSpot JVM works. In either case it shows, how many tunables are supported by your HotSpot JVM, and gives some idea, how to push the optimizations of that JVM further. You get even more flags, when you add -XX:+UnlockDiagnosticVMOptions to -XX:+PrintFlagsFinal.

The downside is, that you don't get any documentation for these flags. But it's a good starting point for further investigation either by web search or by grep'ing through the JVM's source code - if it is available like for the OpenJDK.

FOSDEM 2012 ...

Last weekend FOSDEM 2012 took place at the area of the Université libre de Bruxelles (ULB) - and it's been the first time I've been there. All in all it's been a great and well-organized conference with lots of interesting talks - unfortunately with many interesting ones in parallel ... so, I've missed a lot of them. Here are the talks I've attended.

• On Saturday:
• Ensuring uptime in a small startup: A good talk about some principles on how to ensure uptime during schema updates - based on PostgreSQL, but applies to any relational database.
• An introduction to Ada 2005 and Ada 2012: A time shift back into my days at the university - at least concerning the presentation style: good didactics and very old-style slides. I've never coded in Ada. So, this talk gave me a rough introduction.
• Why Java for Linux Applications?: A very personal talk about the speaker's learnings when trying to develop a GUI for an existing set of programs - and why he failed with C and Gtk+ ending up with Java and Swing.
• Debian packaging for beginners: As I'm working a lot with RPM packaging and have never done packages for Debain-based systems so far, this talk was a good introduction for me.
• Linux Containers and OpenVZ: Nothing really new for me, but a good overview of the current state and the upcoming features.
• Garbage Collection Visualization, GCSpy and NetBeans in tandem: I expected a bit more hands-on, as I spent a lot of time on GC optimization for various JVM scenarios. But GCSpy seems to be a project worth looking at in the near future.

Winter impressions at the ULB area

• On Sunday:
• Sphinx Users stories and How to offload MySQL server with Sphinx: Very interesting for me, as I'm using Sphinx for enabling fast full-text search on email data stored in a MySQL database.
• MySQL HA reloaded - old tricks and cool new tools to guarantee high availability to your MySQL Servers: A good and surely quite complete overview about the possibilities to ensure MySQL high availability and their limitations.
• Works with persistent graphs using OrientDB: A short and hands-on introduction into OrientDB.
• Bringing monitoring into the 21st century - How to predict problems before they arise: A good talk about adaptive monitoring and why fixed thresholds can be misleading.
• DevOps is not an absolute. It's a range.: A really cool talk about the different nuances of DevOps inspired by real-world experiences.
• The Apache Cassandra storage engine: Not so interesting for me, as I've never used Cassandra before.
• Configuration management and deployment with RPM and YADT: The project I'm partially working on for my current employer. A colleague of mine held this talk and made a good job.

Besides the talks there were many booths from a lot of vendors and organizations.

Beastie, the mascot of BSD operating systems