[POSSIBLY SPAM: SPF] hotspot-gc-use Digest, Vol 143, Issue 1

[Thorsten]

Hello,

So If I understand you correctly you explicitly invoke System.gc() and 
get long pauses for that call. Simple Solution: remove the call to 
System.gc() and tune from there. Worse (possible) solution: try setting 
-XX:+/ExplicitGCInvokesConcurrent/

Setting /ExplicitGCInvokesConcurrent /may or may not have some 
unintended side effects. I strongly recommend to remove all calls to 
System.gc that are not for debugging/maintenance.

Best Regards,

Thorsten

//


Am 28/06/2021 um 19:39 schrieb Stefan Reich:
> Hi Thorsten!
>
> Does MaxGCPauseMillis apply to System.gc() too? I thought this was for 
> the incremental collections.
>
> > Did you parse gc logs or by hand/feel?
>
> What, do you think I'm a beginner??? :D
>
> Joke aside, yes it was just "by feel". I know I should measure it 
> properly. Is timing the call to System.gc() an acceptable way to 
> measure this? As far as I know, it only returns after GC has actually 
> completed.
>
> > If you are certain that you don't need more than 800mb of live 
> objects, limit the maxheap to something like 1.5 gb.
>
> Hmm, I am rather not that certain about that... I'd like to keep the 
> max heap around 6 GB.
>
>
> On Mon, 28 Jun 2021 at 09:35, Thorsten <tg at freigmbh.de 
> <mailto:tg at freigmbh.de>> wrote:
>
>     Hello,
>
>     You should not get seconds long stop the world event. How did you
>     measure the pauses? Did you parse gc logs or by hand/feel?
>
>     The desired max pause for g1 can be tuned using
>
>     |-XX:MaxGCPauseMillis=200|
>
>     |, so 200 ms max pause should be the default.
>     |
>
>     It would be helpfull if you take gc logs and provide them. What
>     java version are you using? In old java versions g1 is fairly bad,
>     quality improves in newer versions.
>
>     You can tune and change the garbage collector using -XX Options,
>     see for example here
>     https://ionutbalosin.com/2020/01/hotspot-jvm-performance-tuning-guidelines/
>     <https://ionutbalosin.com/2020/01/hotspot-jvm-performance-tuning-guidelines/>
>
>     Maybe you find one of the experimental garbage collectors helpfull
>     for your application.
>
>     Another simple "Hack" to tune your gc speed: If you are certain
>     that you don't need more than 800mb of live objects, limit the
>     maxheap to something like 1.5 gb. That way your app is simply
>     unable to collect gigabytes of garbage and your max pauses will go
>     down.
>
>     Best regards,
>
>     Thorsten
>
>
>
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>
>
>
> -- 
> Stefan Reich
> BotCompany.de // Java-based operating systems
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