Minimal Java freezes for JewelStore is about 2%-4% of running time. Jewel store uses very frequent very small (100 bytes) object creation therefor java garbage is very efficient, and only minimal GC freezes.
Freezes longer that 100 Millisecond are very rare.
User data pages are allocated directly from the Unix heap. Which is managed by Jewel store applications.
Java freezes can by analised by a tool garbageCollectionAnalyse that can be loaded from GitHub
Analysis tool example
java -ea -jar ~/nb/garbageCollectionAnalize/dist/garbageCollectionAnalyse.jar file=/var/js/java.log0 threshold=320 biggest quiet
Java log example
1775.232: [GC (Allocation Failure) [PSYoungGen: 36960K->5824K(38400K)] 220904K->190104K(302080K), 0.0143596 secs] [Times: user=0.03 sys=0.00, real=0.01 s
1775.247: Total time for which application threads were stopped: 0.0156556 seconds, Stopping threads took: 0.0009975 seconds
1775.672: [GC (Allocation Failure) [PSYoungGen: 36544K->6048K(36864K)] 220824K->190628K(300544K), 0.0107104 secs] [Times: user=0.02 sys=0.00, real=0.00 s
1775.683: Total time for which application threads were stopped: 0.0112424 seconds, Stopping threads took: 0.0002007 seconds
1776.149: [GC (Allocation Failure) [PSYoungGen: 36768K->5952K(37888K)] 221348K->190840K(301568K), 0.0142509 secs] [Times: user=0.02 sys=0.00, real=0.01 s
1776.163: Total time for which application threads were stopped: 0.0283298 seconds, Stopping threads took: 0.0137703 seconds
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