Thomas Wuerthinger 

For other QCon blog posts, see QCon live blog table of contents

Tradeoff between what factors optimized

• Startup time
• Peak throughput
• Memory footprint
• Maximizing request latency
• Packaging size (matters for mobile)
• Can usually optimize a few (but not all) of these

GraalVM

• Supports JVM languages, Rubby, Python, C, Rust, R etc
• Can embed in node js, oracle database
• Standalone binary
• Community Edition and Enterprise Edition
• Can run with Open JDK using Graal JIT compiler or AOT (ahead of time compiling)

AOT

• To use, create new binary with pre-compiled code
• Package classes from app, libraries used and part of the VM
• Iterate adding things until know what need. Then create native executable.
• Uses an order of magnitude less memory than JIT. Saving memory helps when running on AWS Lambda
• CPU usage a lot less up front. Small peak at startup
• JIT compiler has profiling feedback so can do better in the long run. AOT has PGO (profile guided optimizations) to deal with this
• Working on improving – collecting profiles up front, low latency GC option and tracing agent to facilitate configuration

Performance

• Startup time (from start until first request can be served). Two orders of magnitude faster with AOT
• Starting up in less than 50 milliseconds allows spinning up new process upon request
• Hard to measure. Can be lucky/unlucky when get data.
• JIT has an advantage for peak performance. It has profiling data and can make optimistic assumptions. If the assumption not true, can de-optimize/bail out of optimization.

Benchmarks

• Benchmarks are good. Should have more
• Optimizing on too few benchmarks is like overfitting on machine learning
• http://renaissance.dev/ – benchmark suite. Includes Scala and less commonly tested

Choosing

• GraalVM JIT – when need peak throughput, max latency and no config
• GraalVM AOT – use when need fast startup time, small memory footprint and small packaging size

Recommends reading top 10 things to do with GraalVM

Q&A

• Have you considered using Epsilon in benchmark? Not yet. Makes sense since doesn’t do any GC
• Why not use parallel GC? Not sure if it would make a difference. Kirk noted would avoid allocation hit over G1.
• Does AOT make sense for large heaps? Can make sure don’t have disadvantage at least.

My impressions

I had heard about Graal and forgotten a lot. I re-learned much. I like the list of steps slides and the diagram. I feel like it will be more memorable this time. I also liked the comparison at the end on impact of the dimensions covered up front.