Let us assume we have a requirement stating that all jobs must be processed in under 1,000 ms. Knowing that the actual job processing takes just 100 ms we can simplify and deduct the latency requirement for individual GC pauses. Our requirement now states that no GC pause can stop the application threads for longer than 900 ms. Answering this question is easy, one would just need to parse the GC log files and find the maximum pause time for an individual GC pause.
Looking again at the three configuration options used in the test:
| Heap | GC Algorithm | Useful work | Longest pause |
|---|---|---|---|
| -Xmx12g | -XX:+UseConcMarkSweepGC | 89.8% | 560 ms |
| -Xmx12g | -XX:+UseParallelGC | 91.5% | 1,104 ms |
| -Xmx8g | -XX:+UseConcMarkSweepGC | 66.3% | 1,610 ms |
we can see that there is one configuration that already matches this requirement. Running the code with:
java -Xmx12g -XX:+UseConcMarkSweepGC Producer
results in a maximum GC pause of 560 ms, which nicely passes the 900 ms threshold set for satisfying the latency requirement. If neither the throughput nor the capacity requirements are violated, we can conclude that we have fulfilled our GC tuning task and can finish the tuning exercise.
