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Can anyone shed some light on how/why running the same Java apps in a docker container significantly increased the memory footprint? Is JVM overhead shared whe

• haldean 11y ago
  A lot of it is, yes. The JVM loads a large number of largeish class files when it starts; these contain implementations of the standard library and whatever else is on your classpath that you've imported. These have the nice property that they're read-only, though, so multiple JVM processes can safely share them. When you move to sandboxing each JVM off by itself, you lose the ability for them to share memory (which is, in a sense, a _feature_ of sandboxing), so now each of them has to take the 50-100MB hit of those formerly-shared memory regions. (Note that the huge size of the classes is also the big reason why JVM startup time is so crap; another reason that multitenant JVM systems are great is that every process after the first starts much faster)
• lobster_johnson 11y ago
  Assuming this is referrring to the fact that separate containers will link in separate copies of all the binaries (executable + shared libraries), instead of sharing the pages across all instances of he JVM. There's no way for the kernel to know that they're all the same files. So a lot of code is duplicated.