Hi Thorsten, yes I used to call System.gc() once a minute. I just like to see correct heap usages. However, for the server, I removed the call because I didn't like the delays (they are around or slightly above 2 seconds BTW - actually measured this tiime :).
I have just tried XX:+ExplicitGCInvokesConcurrent. I think it's good; seems to do the job. So my problem may actually be solved. I'll keep monitoring. > Setting *ExplicitGCInvokesConcurrent *may or may not have some unintended side effects. Please elaborate, what could those be? I am not aware of any side effects. I need concrete information. Best wishes, Stefan On Tue, 29 Jun 2021 at 09:16, Thorsten <t...@freigmbh.de> wrote: > 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 <t...@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/ >> >> 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 >> >> >> >> _______________________________________________ >> hotspot-gc-use mailing list >> hotspot-gc-use@openjdk.java.net >> https://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use >> > > > -- > Stefan Reich > BotCompany.de // Java-based operating systems > > -- Stefan Reich BotCompany.de // Java-based operating systems
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