Garbage Collectors, Part 2

(The default settings are usually good enough?)

Some tips:

• Understand the trade-off among parameters (heap sizes, etc.)
• Understand the characteristics of a GC algorithm.
• Try adaptive tuning first (you set a goal and JVM adjusts parameters to meet the goal).

Ask yourself:

• Are some full GC pauses tolerable?
  • If so, choose the throughput collector.
  • If not, choose a concurrent collector (CMS or G1).
• Do the default settings yield the performance you need?
  • If not, is GC the bottleneck (check GC logs)? 3% CPU time on GC is a good threshold.
  • Even if GC is not the bottleneck, you still might want to reduce outliers (extreme long puases).
• Do the pause times close to your goal?
  • If so, you might also want to adjust maximum pause time.
  • If not, you might trade some throughput for shorter pause times by reducing the size of the young generation.
• Do you need higher throughput even though the pause times are short?
  • Increase the size of the heap (or at least the size of the young generation).
• Are full GCs due to concurrent-mode failures?
  • Ask for more GC threads or sooner background sweep.
• Are full GCs due to promotion failures?
  • Fragmentation! What can we do about it?