Arjen, On Oct 20, 2015 4:35 PM, "Arjen van der Meijden" <acmmail...@tweakers.net> wrote: > > Afaik, in modern JVM versions, many of the 'old' recommendations may not > really apply anymore or even reduce performance. The book 'Java > Performance: The Definitive Guide' for instance has this statement on > heap sizing: > > "1. The JVM will attempt to find a reasonable minimum and maximum heap > size based on the machine it is running on. > 2. Unless the application needs a larger heap than the default, consider > tuning the performance goals of a GC algorithm (given in the next > chapter) rather than fine-tuning the heap size." > > So basically; see how it works first without specifying any limit (so > not 1GB either) and/or fiddle with the goals rather than the size of the > heap. If you need a certain minimum heap, for instance to offer > sufficient space for the 'memory'-store of ActiveMQ, you should > obviously specify at least that. > > -XX:+UseTLAB; is enabled by default, so specifying it won't do anything :) > > -Xms2G and -Xmx2G; forcing the min and max to the same value is not a > necessity for modern JVM's, it will also force the JVM in making > (potentially) less than optimal allocations for the various areas in the > HEAP and disable automatic resizing. On the other hand, it allows the > JVM to skip the resizing process altogether, so it can gain a bit > performance because of that as well.
I removed the options that you mentioned above, and I see that min heap is 500kb and max is 8GB, and jvisualvm confirms that my app maxes out at 500kb when monitoring 12+ hours. Thanks for the recommendation. It's interesting, prior to these changes that I did, above, my app was starting to max out at 1.5 GB over some number of hours (or days). > > -XX:+UseConcMarkSweepGC; this GC-variant will reduce pause times, but on > the cost of more cpu (although that may be worth it) and a bit less > effective GC (compared to the parallel GC). If your application is > sensitive to those long pauzes (which may be noticable at both the > producer and consumer sides) selecting either CMS or G1 may indeed be a > good choice. For heaps below 4GB, CMS is expected to outperform G1 > (although that statement doesn't say G1 will always outperform CMS for > heaps above 4GB). So, now I'm wondering if I should set max to 4GB, since my app maxes out at 500kb, and based on what you mentioned/recommended above. > > Best regards, > > Arjen > > On 20-10-2015 21:51, Howard W. Smith, Jr. wrote: > > My recommendation (what i'm using for my java web app using latest Java 8 > > version): > > > > -Xms2G > > -Xmx2G > > -XX:+UseTLAB > > -XX:+UseConcMarkSweepGC > > -XX:+CMSClassUnloadingEnabled > > > > I've seen it recommended to make min and max the same value for best GC, > > but feel free to google/confirm that. :) > > > > > >
