Introducing fasthat: A faster Java heap analyser Chris K. Jester-Young cky@on-site.com @cky944 May 2012

What I do at On-Site ● Part of Performance Engineering team ○ One of the many hats I wear ● Keep the site fast and stable ● Major sources of performance issues: ○ Database queries ○ Concurrency bugs ○ Using the wrong algorithms ○ GC thrashing due to memory leaks ● The last one plagued us for a long time

Why I love JRuby ● All the power of Ruby ● All the platform support of JVM ○ Reuse many useful Java class libraries ○ Debugging and profiling APIs ○ hprof, jhat, etc. ● ...but many of these don't support JRuby well ● Luckily, OpenJDK is, well, open-source ○ Tweak it till it works

So I did my own thing ● Faster ○ Uses non-JDK Rhino for OQL queries ○ Uses more optimal data structures from Guava and newer JDK ● Enable histogram referrer tracing ● Peek into data structures like arrays and hashes---even Ruby ones! ○ Currently shallow only

Areas for improvement ● Support deep data structure peeking ● Find version-independent ways to peek ● Support Ruby class hierarchies ● Support Ruby stack traces ○ ...intermingled with Java stack frames ● Support other languages

Love low-level hacking? ● https://github.com/on-site/fasthat ● Or, come work with us! class << please = Object.new def us puts "Send your resume to: jruby-#{yield}@on-site.com" end end if your_resume = "rocks" please.send(:us) { your_resume } end