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JVM tuning (especially the GC and memory allocation scaling) can be a huge PITA.



But having options is always good, isn't the same with compiled languages? you keep the defaults options but if you want extra performance you try different compiler flags or different compiler if the language has more then one.


Honestly I’d rather have good defaults than lots of options. If one tool meets requirements out of the box, then it’s preferable to a tool that requires a lot of tooling.


But if you do not have options then what is a "good default" , you have a default option if you have more then an option, so you prefer software with no options?

Can you give examples of languages(compilers or VMs with bad defaults in your opinion?


Java by default has a hard memory limit which when hit causes services to hang in a semi-responsive state rather than exiting cleanly, requiring every user to hand-tune limits and carefully setup health checks and monitoring. Two decades in, they added a non-standard option to instead exit.

If they had instead made the default to act like almost everything else it would have worked with standard process monitors and limits with no effort required and a substantial fraction of the downtime I’ve seen for Java applications would never have happened.


Isn't this default better for average Joe that runs a Java desktop app, and developers that deploy apps should know how to change this defaults?


How is it better for something to stop working but not exit? It’s exceedingly uncommon for anyone to have correct handling for OOM exceptions so the most likely effect is that stuff partially works - servers accept requests but never respond, apps have menus/buttons which don’t work, etc.

Similarly, if developers who deployed apps knew enough to avoid this, we’d know by now because it wouldn’t happen so frequently. It does highlight who failed to do real health-checks (e.g. years ago most Hadoop services needed huge amounts of RAM to start without crashing but they’d be listed as okay) but it’s the kind of thing sysadmins have been cleaning up for decades.


You are probably right for this case, my initial comment was related to performance tuning configuration, the comment I replied sounded like JVM should have had X set to my preferred value or "I prefer software that has no options to confuse me with aka GNOME mentality"


You can have options and have good default values for those options. Good default values are those that are reasonable for most people most of the time such that they don't need to be (or hire) domain experts to properly configure their tool.

My opinion of a bad default would include a language toolchain which defaults to dynamic linking and requires one to opt into static linking (Java, Python, JS, etc, etc, etc). Worse than that is an anorexic toolchain that has no defaults whatsoever and requires you to pass every little detail directly to the compiler--bonus points if your language has a massive ecosystem of competing tools which are meant to manage these sorts of details for you but utterly and uniformly fail to do so (looking at you, C/C++).


So the JVM run-time is installed and used by average people, so the defaults should be set for this people that install Java to run a desktop app IMO, the developers that want extra performance should read the manual and configure things.


I’ve never heard of a runtime that forces a dichotomy between end-user- and developer-friendliness (putting aside for the moment that end users are famously annoyed by the Java runtime). Rust, Go, etc don’t have runtimes which force a choice between end-users and developers...


JVM can be used for Desktop, server and in the past applets , it would be impossible to find a configuration that is optimal for all applications, so competent developers would tweak the defaults or use different deployment methods like AOT compilation or bundle your own JVM , is your problem that JVM is used in so many different places that different algorithms, runtimes and optimization were created for it ? Your examples of Go and Rust are of languages that are so far not been used in such diverse places, there are no good alternative compilers but something like Python has such a diversity of runtimes.


How much is that actually necessary these days? I remember spending ages tweaking flags in the 1.4 - 1.6 years. But there have increasingly been sensible defaults with broad applicability. Now that G1 is both default and usable, even more so.

As i've moved onto 11, i've slashed our apps' JAVA_OPTS down to almost nothing - max heap size, some GC logging flags, that's it.


At scale? Very necessary. The default GC as of Java 8 (the last version I used in production) suffered significant performance issues above 40 GB of working set, and required careful tuning thereafter.


I completely agree. The JVM is fine until it isn't, and at that point it becomes very frustrating to deal with - even when using less than 16GB RAM.


The default GC as of OpenJDK 8.

The default GC from IBM, Azul, and others wasn't the same one.

In fact Azul has made a business of selling JVMs with GC that can handle hundreds of data GBs.

Modern OpenJDK versions also have such GCs now.


Hardly any different that having to use VTune or perf to optimise C and C++, which require the added steps of recompiling with different flags and redemploying.


I wouldn’t recommend C or C++, but in their defense, you don’t need to worry about tuning as soon as you do on the JVM. Many apps won’t need to bother with it at all (which is good because C/C++ programmers have all manner of other things to worry about that aren’t a concern for modern languages).


There's also a notion of failure mode for improperly tuned apps. This is certainly a personal preference, but I prefer true failures over constraint failures. I'd rather OOM in golang than run out of threads in my Java execution context while having plenty of free memory. At least when starting out.


Me neither, I do like Rust and see its adoption at NPM as good PR for the language, however I also think that the way the decision process went wasn't free of bias.




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