Optimal Garbage Collector settings for large heaps?

[vdzhuvinov]

Are there any recommended settings for the JVM to reduce the likelyhood and the effect of stop-the-world GC events? Pauses in the order of several minutes and more have been observed on a 15GB heap.

[nadirx]

Ah, JVM tuning is one of those arcane subjects

At any rate a 15GB heap should not give you such long pauses if the JVM is tuned properly.

Here are some tips:

CMS Tuning

• Always turn off adaptive sizing (-Xms=-Xmx)
• Manually tune for smaller young generation
• -XX:NewSize=-XX:MaxNewSize - start 1/8 heap (2GB max)
• CMS balancing act
• Smaller new size => decrease throughput
• Larger new size => Risk of stop-the-world
• Increase the Eden size -XX:SurvivorRatio=16 (or 32)
• Concurrent Mode Failure (gc logs)
  • Increase the heap size
  • Increase the old generation
  • Start CMS earlier: -XX:CMSInitiatingOccupancyFraction=60 -XX:+UseCMSInitiatingOccupancyOnly
• Insufficient heap size (> 50% live data)
  • Sawtooth pattern (VisualVM)
  • Increase the NewSize

G1 Tuning

• Always turn off adaptive sizing (-Xms=Xmx)
• Tune the pause time (–XX:MaxGCPauseMillis) to meet the 90th percentile for your SLA
• Starting points: 500ms for 32GB, 1000ms for 64GB
• Larger values increase the throughput
• Stop-the-world Pauses “Full GCs”, “to-space overflow/exhausted”
• Increase –XX:MaxGCPauseMillis
  • Increase the heap size
  • Modify -XX:InitiatingHeapOccupancyPercent (default 45)
    • But not lower than the % of live data!
  • Increase -XX:ConcGCThreads

OS Tuning

• Use Huge Pages
  • Enable on the JVM level -XX:+UseLargePages
  • Enable at the OS level
  • Verify “java -Xmx<JDG max heap size>g -XX:+UseLargePages -version”
  • Disable Transparent Huge Pages