Shenandoah: How small is small?

[Christine Flood]

Our original target was for heaps of > 20gb, however we often run our tests in 4gb or less and the performance is acceptable.

However if you are currently seeing only minor gc pauses and they are in the < 16ms range, I'm not sure Shenandoah can help.  However if you are seeing full gcs of more than that then it might be worth considering.

Christine


----- Original Message -----
> From: "org openjdk" <org.openjdk at io7m.com>
> To: shenandoah-dev at openjdk.java.net
> Sent: Thursday, November 17, 2016 10:25:34 AM
> Subject: Fw: Shenandoah: How small is small?
> 
> [Reposting to shenandoah-dev@ on the advice of Martijn Verburg]
> 
> Hello.
> 
> I've been watching the development of Shenandoah since it began. As a
> developer of software with mildly soft-realtime requirements (games,
> primarily), I'm always eager to see advances that can reduce GC pause
> times. Although right now I don't have a GC problem (typically, my
> pauses for minor GCs are well below 16ms and therefore are not
> perceptible given the usual 30hz/60hz game loop), I still feel that I
> have to be more conscious of allocation rates than feels natural in
> order to avoid producing too much garbage. I sometimes find myself
> avoiding better abstractions and immutable objects simply because I
> want to avoid allocations. Escape analysis helps, but sometimes those
> objects really do need to hang around. Value types will also help!
> 
> I've read in JEP 189 that Shenandoah is intended to try to reduce pause
> times on +100gb heaps, and a rather outdated blog post online [0]
> suggested that a 512mb heap is simply too small to run at all. The
> software I write is written under the general assumption that 1GB of
> memory will be a minimum requirement - this includes both the JVM heap
> and any allocated native memory.
> 
> Right now I'm still using ParNew, although I'll likely move to G1 if it
> becomes the default in JDK9. Is Shenandoah likely to be an improvement
> for my use case?
> 
> Regards,
> Mark
> 
> [0]
> https://www.jclarity.com/2014/03/12/shenandoah-experiment-1-will-it-run-pcgen/
>