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IBM Expert TV: Tune Java Garbage Collection to improve performance
By
Kevin Grigorenko
posted
Thu April 14, 2022 10:44 AM
1
Like
On Wednesday, April 13th, 2022 at 11:00 AM ET, we presented "Tune Java Garbage Collection to improve performance" on IBM Expert TV.
Replay:
https://ibm.biz/BdPBhT
Presentation:
https://ibm.biz/BdPdEJ
Speakers: Kevin Grigorenko, Gary DeVal
In the presentation, we discussed key aspects of garbage collection tuning to improve performance. We started by explaining that garbage collection (GC) is a critical component of Java performance which generally cannot be disabled, so it must be tuned. It's important to be data driven and the key data for tuning GC is verbose GC. This generally has an overhead of less than ~0.2% and is recommended for all environments. Next, use the free
IBM Garbage Collection and Memory Visualizer
tool to load the verbosegc files and review the proportion of time spent in garbage collection. A healthy proportion is generally less than 5-10%. If you observe a greater proportion, then consider various strategies for tuning:
Consider testing different garbage collectors themselves; on IBM Java and Semeru/OpenJ9, those include gencon (default), balanced, optthruput, optavgpause, and metronome.
The maximum heap size is tuned with -Xmx or -XX:MaxRAMPercentage
If used tenured heap > ~70% after global GCs, test increasing max heap size
The maximum nursery size is tuned with -Xmn (defaults to 25% of -Xmx)
If used tenured heap < ~40% after global GCs, test increasing max nursery size
Check for long GC pauses - find/fix cause
Eliminate system GCs
Reduce class loading/unloading churn
Make sure Java process size fits in RAM; paging has massive performance impact
Gencon: If you're willing to trade throughput/CPU for reduced nursery pause times, test -Xgc:concurrentScavenge
#websphere
#WebSphereApplicationServer
#WebSphereLiberty
#experttv
#Java
#performance
#WebSphere-performance
#java-performance
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