Does GraalVM native image increase overall application performance or just reduce startup times?

Question

I’m looking at compiling my Java app using a GraalVM native image but all the documentation I have seen refers to reduced startup times but make no reference to improvements in overall application performance?

So what can I realistically look forward to by doing this?

Answer 1

In general, the performance decreases. I have reported the performance decrease of native images some time ago to the GraalVM team. The severity of performance decrease may vary on the use case(s). On the benchmarks I have written and used for my analysis (an updated version of the code can be found here), the overhead ranged from "barely noticeable" to "up to 5x slower". I also mentioned this shortly in my talk at JCON 2019 (#shamelessSelfPromotion).

There is a nice slide from the GraalVM team, illustrating what technology to use for which use case: (The image was taken from a tweet by Thomas Würthinger)

For the interested reader: As Andrew mentioned on github, a major factor of the bad performance is the non-existence of JIT-compilation: the JIT-compiler can, among other things, eliminate seldom-used branches and thus significantly speed up performance. This is obviously not possible with natively compiled code.

Side note: While we are on the topic of performance, you can execute bitcode emitted by clang (i.e. execute C/C++ programs on GraalVM), but don't expect "good" performance at all... 😜