This is presentation for Cogniance Java Evening 13.02.2013. My related to topic article you can find here (russian) : http://habrahabr.ru/post/160049/

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

17. -XX:+DoEscapeAnalysis

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