JVM performance options.
How it works?
Dmitriy DumanskiyCogniance, Velti project
Java Team Lead
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
Options may vary per
architecture / OS / JVM version
JVM 6 ~ 730 options
JVM 7 ~ 680 options
-X : are non-standard (not all JVM)
-XX : are not stable
Boolean : -XX:+<option> or -XX:-<option>
Numeric : -XX:<option>=<number>
String : -XX:<option>=<string>
Types
Categories
Behavioral options
Garbage Collection options
Performance tuning options
Debugging options
Analys : Can objects be created on stack?
Are objects accessed from 1 thread?
-XX:+DoEscapeAnalysis
Analys result : GlobalEscape
ArgEscape
NoEscape
-XX:+DoEscapeAnalysis
NoEscape
class Cursor {
String icon;
int x;
public void create() {
Cursor c = new Cursor(); //HEAP
c.icon = null; //HEAP
c.x = 0; //HEAP
}
}
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
}
}
NoEscape → scalar replacement
NoEscape → scalar replacement
-XX:+DoEscapeAnalysis
~20-60% locks elimination
~15-20% performance improvement
-XX:+DoEscapeAnalysis
-XX:+AggressiveOpts
-AggressiveOpts +AggressiveOpts
AutoBoxCacheMax 128 20000
BiasedLockingStartupDelay 4000 500
EliminateAutoBox false true
OptimizeFill false true
OptimizeStringConcat false true
-XX:AutoBoxCacheMax=size
class Integer {public static Integer valueOf(int i) {
if(i >= -128 && i <= IntegerCache.high) return IntegerCache.cache[i + 128]; else return new Integer(i); }}
Sets IntegerCache.high value :
-XX:AutoBoxCacheMax=size
new Integer(1) vs Integer.valueOf(1)
valueOf ~4 times faster
-XX:BiasedLockingStartupDelay=delay
Biased
Thin
Fat
-XX:-OptimizeStringConcatString twenty = «12345678901234567890»;
String sb = twenty + twenty + twenty + twenty;
String twenty = «12345678901234567890»;String sb = new StringBuilder().append(twenty).append(twenty).append(twenty).append(twenty).toString();
-XX:-OptimizeStringConcatString 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];
-XX:+OptimizeStringConcatString twenty = «12345678901234567890»;
String sb = new StringBuilder()
.append(twenty).append(twenty)
.append(twenty).append(twenty).toString();
new char[80];
-XX:+OptimizeStringConcatString twenty = «12345678901234567890»;
StringBuilder sb1 = new StringBuilder();
sb1.append(new StringBuilder()
.append(twenty).append(twenty)
.append(twenty).append(twenty)
);
new char[80];
XX:+OptimizeFillArrays.fill(), Arrays.copyOf() or code patterns :
for (int i = fromIndex; i < toIndex; i++) {
a[i] = val;
}
Native machine instructions
XX:+EliminateAutoBox
Removes unnecessary AutoBox operations
Works only for Integers
-XX:+UseStringCache
Look like not used anymore
-XX:+UseCompressedStrings
For ASCII characters:
char[] -> byte[]
-XX:+UseCompressedOops
Heap size up to 32GbReferences size 50% smallerJVM performance boost 2-10%20 — 60% less memory consumption;
-XX:+UseCompressedOops
32-bit 64-bit 64-bit Comp.0
0.2
0.4
0.6
0.8
1
1.2
-XX:+EliminateLocks
synchronized (object) { //doSomething1}synchronized (object) { //doSomething2}
synchronized (object) { //doSomething1 //doSomething2}
-XX:+EliminateLockssynchronized (object) { //doSomething1}
//doSomething2
synchronized (object) { //doSomething3}
synchronized (object) { //doSomething1 //doSomething2 //doSomething3}
-XX:+UseLargePages
Translation-Lookaside Buffer (TLB) is a page translation cache that holds the most-
recently used virtual-to-physical address translations
-XX:CompileThreshold=n
Client mode n = 1500
Server mode n = 10000
More profile data — more optimizations
-XX:hashCode=n
Object.hashCode() - internal address of the object?
-XX:hashCode=nn is :
0 – Park-Miller RNG (default) 1 – f (address, global state) 2 – const 1 3 – sequence counter 4 – object address 5 – Thread-local Xorshift
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