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.
