JVM performance options. How it works
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The document discusses JVM performance options, including various flags and their configurations for garbage collection, performance tuning, and debugging. It details the impact of specific options like escape analysis, autoboxing, and optimized string concatenation on performance improvements. Additionally, it highlights memory optimization techniques such as compressed object pointers and large pages for enhancing JVM efficiency.
![-XX:AutoBoxCacheMax=size
Sets IntegerCache.high value :
class Integer {
public static Integer valueOf(int i) {
if(i >= -128 && i <= IntegerCache.high)
return IntegerCache.cache[i + 128];
else
return new Integer(i);
}
}](https://image.slidesharecdn.com/jvmoptions-130213134018-phpapp02/85/JVM-performance-options-How-it-works-19-320.jpg)
![-XX:-OptimizeStringConcat
String twenty = «12345678901234567890»;
String sb = new StringBuilder()
.append(twenty).append(twenty)
.append(twenty).append(twenty).toString();
new char[16];
new char[34];
new char[70];
new char[142];](https://image.slidesharecdn.com/jvmoptions-130213134018-phpapp02/85/JVM-performance-options-How-it-works-23-320.jpg)
![-XX:+OptimizeStringConcat
String twenty = «12345678901234567890»;
String sb = new StringBuilder()
.append(twenty).append(twenty)
.append(twenty).append(twenty).toString();
new char[80];](https://image.slidesharecdn.com/jvmoptions-130213134018-phpapp02/85/JVM-performance-options-How-it-works-24-320.jpg)
![-XX:+OptimizeStringConcat
String twenty = «12345678901234567890»;
StringBuilder sb1 = new StringBuilder();
sb1.append(new StringBuilder()
.append(twenty).append(twenty)
.append(twenty).append(twenty)
);
new char[80];](https://image.slidesharecdn.com/jvmoptions-130213134018-phpapp02/85/JVM-performance-options-How-it-works-25-320.jpg)
![XX:+OptimizeFill
Arrays.fill(), Arrays.copyOf() or code
patterns :
for (int i = fromIndex; i < toIndex; i++) {
a[i] = val;
}
Native machine instructions](https://image.slidesharecdn.com/jvmoptions-130213134018-phpapp02/85/JVM-performance-options-How-it-works-26-320.jpg)
![-XX:+UseCompressedStrings
For ASCII characters:
char[] -> byte[]](https://image.slidesharecdn.com/jvmoptions-130213134018-phpapp02/85/JVM-performance-options-How-it-works-29-320.jpg)
JVM performance options. How it works
- 1. JVM performance options. How it works?
- 2. Dmitriy Dumanskiy Cogniance, Velti project Java Team Lead
- 3. Xmx2048M -Xms2048M -XX:ParallelGCThreads=8 -Xincgc -XX:+UseConcMarkSweepGC -XX: +UseParNewGC -XX:+CMSIncrementalPacing -XX:+AggressiveOpts -XX:+CMSParallelRemarkEnabled -XX:+DisableExplicitGC -XX:MaxGCPauseMillis=500 -XX:SurvivorRatio=16 -XX:TargetSurvivorRatio=90 -XX:+UseAdaptiveGCBoundary -XX:-UseGCOverheadLimit -Xnoclassgc -XX:UseSSE=3 -XX:PermSize=128m -XX:LargePageSizeInBytes=4m
- 5. Options may vary per architecture / OS / JVM version
- 6. JVM 6 ~ 730 options JVM 7 ~ 680 options
- 7. -X : are non-standard (not all JVM) -XX : are not stable
- 8. Types Boolean : -XX:+<option> or -XX:-<option> Numeric : -XX:<option>=<number> String : -XX:<option>=<string>
- 9. Categories Behavioral options Garbage Collection options Performance tuning options Debugging options
- 10. -XX:+DoEscapeAnalysis Analys : Can objects be created on stack? Are objects accessed from 1 thread?
- 11. -XX:+DoEscapeAnalysis Analys result : GlobalEscape ArgEscape NoEscape
- 12. NoEscape class Cursor { String icon; int x; public void create() { Cursor c = new Cursor(); //HEAP c.icon = null; //HEAP c.x = 0; //HEAP } }
- 13. NoEscape → scalar replacement class Cursor { String icon; int x; public void create() { String icon = null; //ref on stack frame int x = 0; //int on stack frame } }
- 14. NoEscape → scalar replacement
- 15. NoEscape → scalar replacement
- 16. -XX:+DoEscapeAnalysis ~20-60% locks elimination ~15-20% performance improvement
- 18. -XX:+AggressiveOpts -AggressiveOpts +AggressiveOpts AutoBoxCacheMax 128 20000 BiasedLockingStartupDelay 4000 500 EliminateAutoBox false true OptimizeFill false true OptimizeStringConcat false true
- 19. -XX:AutoBoxCacheMax=size Sets IntegerCache.high value : class Integer { public static Integer valueOf(int i) { if(i >= -128 && i <= IntegerCache.high) return IntegerCache.cache[i + 128]; else return new Integer(i); } }
- 20. -XX:AutoBoxCacheMax=size new Integer(1) vs Integer.valueOf(1) valueOf ~4 times faster
- 21. -XX:BiasedLockingStartupDelay=delay Biased Thin Fat
- 22. -XX:-OptimizeStringConcat String twenty = «12345678901234567890»; String sb = twenty + twenty + twenty + twenty; String twenty = «12345678901234567890»; String sb = new StringBuilder() .append(twenty).append(twenty) .append(twenty).append(twenty).toString();
- 23. -XX:-OptimizeStringConcat String twenty = «12345678901234567890»; String sb = new StringBuilder() .append(twenty).append(twenty) .append(twenty).append(twenty).toString(); new char[16]; new char[34]; new char[70]; new char[142];
- 24. -XX:+OptimizeStringConcat String twenty = «12345678901234567890»; String sb = new StringBuilder() .append(twenty).append(twenty) .append(twenty).append(twenty).toString(); new char[80];
- 25. -XX:+OptimizeStringConcat String twenty = «12345678901234567890»; StringBuilder sb1 = new StringBuilder(); sb1.append(new StringBuilder() .append(twenty).append(twenty) .append(twenty).append(twenty) ); new char[80];
- 26. XX:+OptimizeFill Arrays.fill(), Arrays.copyOf() or code patterns : for (int i = fromIndex; i < toIndex; i++) { a[i] = val; } Native machine instructions
- 27. XX:+EliminateAutoBox Removes unnecessary AutoBox operations Works only for Integers
- 28. -XX:+UseStringCache Look like not used anymore
- 29. -XX:+UseCompressedStrings For ASCII characters: char[] -> byte[]
- 30. -XX:+UseCompressedOops Heap size up to 32Gb References size 50% smaller JVM performance boost 2-10% 20 — 60% less memory consumption;
- 31. -XX:+UseCompressedOops 1.2 1 0.8 0.6 0.4 0.2 0 32-bit 64-bit 64-bit Comp.
- 32. -XX:+EliminateLocks synchronized (object) { synchronized (object) { //doSomething1 //doSomething1 } //doSomething2 synchronized (object) { } //doSomething2 }
- 33. -XX:+EliminateLocks synchronized (object) { //doSomething1 } synchronized (object) { //doSomething1 //doSomething2 //doSomething2 //doSomething3 synchronized (object) { } //doSomething3 }
- 34. -XX:+UseLargePages Translation-Lookaside Buffer (TLB) is a page translation cache that holds the most- recently used virtual-to-physical address translations
- 35. -XX:CompileThreshold=n Client mode n = 1500 Server mode n = 10000 More profile data — more optimizations
- 36. -XX:hashCode=n Object.hashCode() - internal address of the object?
- 37. -XX:hashCode=n n is : 0 – Park-Miller RNG (default) 1 – f (address, global state) 2 – const 1 3 – sequence counter 4 – object address 5 – Thread-local Xorshift