https://www.youtube.com/watch?v=Ce_mEZP1XFk
TL;DW:
Use defaults, usually there is no need to mess with JVM flags!
If you insist changing things:
- Start with defaults
- Measure app behavior
- Change things one by one:
- heap size
- number of helper threads
- garbage collector
Know the defaults!
Heap size:
- Initial: 1/64 of real memory
- Max, <250MB available: 1/2 of real memory
- Max, >250MB available: 1/4 of real memory
Helper threads:
- <5 cores: threads = number of cores
- 5+ cores: threads = 5/8 * number of cores
Default Garbage Collector:
- JDK8: ParallelGC (shouldn't be used in the cloud anymore, from pre-container days!)
- JDK11+, 1 CPU and <1728MB memory: SerialGC
- JDK11+, 2+ CPU or >1728MB memory: G1GC
Recommendations
- Set heap size based on allocation rate and live set size
- Ideally, number of active threads = number of cores
- Don't change the default GC ;)
