Gabriel: It's certainly alright to still discuss this. It's a complex issue, with (I think) only very rough solutions.
I agree that the JVM authors are saying that if you cannot know in advance very much about how the Java program is going to be using the JVM, and if you cannot know about the environment in which the JVM runs (how much memory hardware is installed, what kind of CPU or CPUs the JVM is running on, etc) then we should not make assumptions that can easily be incorrect. The JVM could inspect some things at startup time (before the program has a chance to begin running), and can make an educated guess about which GC algorithm to select based only on the hardware it finds. But, we actually do know some things that the JVM can't know before the Java program begins to run. We know that the application is a web server -- this has very large implications. The JVM cannot guess something this significant when it is auto-selecting a GC algorithm during JVM startup. It is true that not every webapp works the same, so to get the best performance for your own webapp you have no choice but to hand-tune the GC. It has always been that way, and still is, regardless of whether we specify a default GC algorithm or not. We also chose a default max heap size, which is pretty low (maybe we could afford a somewhat larger max heap now?). But we know exactly what it is set to, by default, which also tells us more about the hardware configuration before startup. If that default max heap size (still the most coarse tuning knob) is not what the webapp should have, which will often be the case, then the system administrator must edit the defaults file and change it.. and while they're in there they can certainly change the GC algorithm default if they'd like to. About not knowing which CPU(s) are in the machine: most CPUs are now multicore, and much of the worry about single core versus multicore seems to have gone away because even with a single chip you still have multiple processors. About the only assumption we're making here is that we're not trying to choose defaults for old machines. We're assuming at least single chip, multicore. As I said in my first comment: Of course we're only talking about the package defaults and general recommendations, and it is up to the user to carry out some performance testing to find what works best for their webapp(s), with their own performance goals in mind. -- Using incorrect JVM Garbage Collector https://bugs.launchpad.net/bugs/541520 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
