G1 GC for 100GB+ heaps

[Kees Jan Koster]

Dear Bernd

>> Max pause times we aim for is 100ms, which looks to be entirely
>> doable. Maybe we should set our goals a little more aggressively. ;-)
> 
> 100ms sounds very aggressive for such large heaps, I would not expect
> it. And its actually better to not aim for it then as well.

What would you find reasonable for a 100GB heap? And for a 200GB heap? I am not so much interested in the actual value you say, as in the ball-park you are in. We’ll be sure to test for what works best for us.

I’d rather not set it to such a value that the GC cannot work reliably, but we’d like it to be quick to support the front-end document fetch use-case.

What happens when we set this value too low? How does that restrict GC behaviour and what happens?

> Anyway, without seeing your logs and knowing your hardware specs its
> hard to give more hints.

I understand, but you have helped tremendously already. Next round of questions should be with some logs at hand.

> If you have 128GB and aim for a 100GB heap, keep 10GB for the rest of
> the VM then you will have 10GB for filesystem cache. This should be
> reflected in the swappiness setting for linux (5-10 for large machines
> with application server load).

We run with swappiness 10.

I don’t expect much from the file system cache, the access pattern is pretty random and we cache files that are read more than once on the batch processing servers already.

> You might however reserve and turn on real large pages for the VM.
> -XX:+UseLargePages. when using such a large heap it can safe a lot of
> resources.

Will do, thank you.

--
Kees Jan

http://java-monitor.com/
kjkoster at kjkoster.org
+31651838192

Human beings make life so interesting. Do you know that in a universe so full of wonders,
they have managed to invent boredom. Quite astonishing... -- Terry Pratchett

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