I wanted to attent FOSDEM two weeks ago, but couldn’t because I was sick, in bed with fever. I should have done a presentation about Shenandoah. Unfortunately, my backup Andrew Dinn also became sick that weekend, so that presentation simply didn’t happen. I want to summarize some interesting news that I wanted to show there. About Shenandoah’s performance.
When I talked about Shenandoah at FOSDEM 2015, I didn’t really announce any performance numbers, because we would have been embarrassed by them 🙂 We spent the better part of last year optimizing the heck out of it, especially the barriers in the C2 compiler, and here we are, with some great results.
Ok. This doesn’t really exist. The last SPECjvm release was SPECjvm2008. Unfortunately, SPEC doesn’t seem to care about SPECjvm anymore, which means the last Java version that runs it without any modifications is Java7. We did some small fixes, that allows it to run with Java9 too. This invalidates compliance of the results. But they are still tremendously useful for comparison. So here it comes:
This was run on a 32 core box with 160GB of RAM, giving the JVM 140GB of heap. Exact same JVM and settings with G1 and Shenandoah. No special tuning parameters.
In terms of numbers, we get:
Throughput: Shenandoah: 374 ops/m vs. G1: 393 ops/m (95%, min 80%, max 140%)
Pauses: Shenandoah: avg: 41 ms, max 202 ms G1: avg: 240 ms, max 1126 ms
This means, throughput of Java apps, running with Shenandoah is on average 95% that of G1, depending on the actual application, it’ll range from around 80% to around 140%. However, pause times on such large heaps are significantly better with Shenandoah!
SPECjbb2015 measures throughput of a simulated shop system under response time constraints, or service level agreements (SLAs). It measures ‘max-jops’ which is maximum throughput of the system without SLA, and critical-jops, which is throughput of the system under a restrictive SLA. Here are the numbers, G1 vs. Shenandoah, same machine and JVM settings as above:
This basically confirms the results that we got from SPECjvm2008: general throughput in the area of 95% behind G1, but much better pause times, reflected in a much higher score of critical-jops.
Other exciting news is that Shenandoah is now stable enough that we want to encourage everybody who’s interested to try it out. The nice folks at Adopt-OpenJDK have set up a nightly build from where you can grab binaries (Shenandoah JDK8 or Shenandoah JDK9). Enjoy! (And please report back if you encounter any problems!)