README.md

Exploring the GraalVM JIT

Estimated time: 10 minutes.

Let's continue to experiment on the example project we created before.

Locate the sample project we created:

cd primes-web

We have the project built and can run it with the java like this:

java -jar build/libs/primes-web-0.1-all.jar

There's a number of options available to turn on the additional logging about the compiler events, which you can find in the docs.

One particular options is interesting to check if a certain piece of code you're interested in get to the JIT: -Dgraal.PrintCompilation=true.

Run the application like this and we'll see a bunch of output that we can interpret:

java -Dgraal.PrintCompilation=true -jar build/libs/primes-web-0.1-all.jar

Now to inspect the actual optimizations the compiler does you can enable GraalVM to dump the compiler graphs for the code it processes.

java -Dgraal.Dump=:2 -Dgraal.MethodFilter=PrimesController.* -jar build/libs/primes-web-0.1-all.jar

This enables the dump and filters it to only contain the interesting classes in our app.

Apply the load:

hey -z 60s http://localhost:8080/primes/random/100

Check the log for the location of the files, a line like:

Dumping IGV graphs in /home/opc/primes-web/graal_dumps/2020.11.25.12.42.21.147

Download the .bgv files.

Run the idealgraphvizualizer locally, it's GUI application, load the graphs into it.

Explore the transformations.

Next, we'll try to learn about the polyglot nature of GraalVM.