If memory usage matters to you, have you tried telling the JVM not to use all the memory? Have you tried any of the tuning options? Can't say I've ever used app engine, but the pure java applications I've worked on did in fact use a fair bit of memory, much like windows and OSX will aggressively use spare memory for caching. Then I use -Xmx to tell it not to use all the memory and now it's much better. For a server, I'd say that this is both expected and the correct behaviour.
I have, and gave up after a month of touching every couple of days trying to find the sweet spot. Someone more familiar with JVM internals would have probably succeeded - but somehow C Python Go and even OCaml runtimes don't need this level of tuning in my experience.
JVM deployments tend to assume nothing else happens on the same machine, in my experience.
You last point is probably true. In every application I have ever deployed I only ever set the Xmx and J-Server settings, I never faced any problems. You need to give the GC some breathing room though.
> As an added annoyance, which is specific to App Engine but a result of using the JVM, it's impossible to specify JAVA_OPTS, so any of the -X flags, without switching to the Flexible environment
I haven't used App Engine either but I suspect that the flexible environment is more expensive.
I use -Xmx and then the process crashes because it runs out of memory. It's very wasteful with memory and I wish jep 169 was implemented to mitigate it. It's unfortunate that it was written in 2012 and remains a draft.
