幾中垃圾收集器組合測試

阿新 • • 發佈：2019-01-17

測試程式碼：

public class demonopara {

private static final int _1MB = 1024*1024;

public static void main(String[] args) {

// TODO Auto-generated method stub

byte[] allocation1,allocation2,allocation3,allocation4;

allocation1 = new byte[2 * _1MB];

allocation2 = new byte[2 * _1MB];

allocation3 = new byte[2 * _1MB];

allocation4 = new byte[4 * _1MB];

}

JVM引數：-verbose:gc -Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8

(堆大小20M，不可拓展，10M新生代，10M老生代，Eden和Survivor的比例是8：1，OK)

1.Parallel Scavenge + Serial Old(-XX:+UseParallelGC)

Heap

PSYoungGen total 9216K, used 7159K [0x00000007ff600000, 0x0000000800000000, 0x0000000800000000)

eden space 8192K, 87% used [0x00000007ff600000,0x00000007ffcfde20,0x00000007ffe00000)

from space 1024K, 0% used [0x00000007fff00000,0x00000007fff00000,0x0000000800000000)

to space 1024K, 0% used [0x00000007ffe00000,0x00000007ffe00000,0x00000007fff00000)

ParOldGen total 10240K, used 4096K [0x00000007fec00000, 0x00000007ff600000, 0x00000007ff600000)

object space 10240K, 40% used [0x00000007fec00000,0x00000007ff000010,0x00000007ff600000)

PSPermGen total 21504K, used 2611K [0x00000007f9a00000, 0x00000007faf00000, 0x00000007fec00000)

object space 21504K, 12% used [0x00000007f9a00000,0x00000007f9c8cc78,0x00000007faf00000)

//前三個物件allocation1,allocation2,allocation3都分配到了，Eden區，第四個4M的直接去了老生代。。。 //-XX：+PretenureSizeThreshold 直接晉升老生代的物件的大小，設定這個引數後，大於這個引數的物件直接在老生代分配。但是！！！請注意！！！PretenureSizeThreshold這個引數只對Serial和parNew有用，Parallel Scavenge不認識他。。

2.Serial+Serial Old(-XX:+UseSerialGC)

[GC[DefNew: 6995K->240K(9216K), 0.0044170 secs] 6995K->6384K(19456K), 0.0044380 secs] [Times: user=0.01 sys=0.01, real=0.01 secs]

Heap

def new generation total 9216K, used 4666K [0x00000007f9a00000, 0x00000007fa400000, 0x00000007fa400000)

eden space 8192K, 54% used [0x00000007f9a00000, 0x00000007f9e527b0, 0x00000007fa200000)

from space 1024K, 23% used [0x00000007fa300000, 0x00000007fa33c198, 0x00000007fa400000)

to space 1024K, 0% used [0x00000007fa200000, 0x00000007fa200000, 0x00000007fa300000)

tenured generation total 10240K, used 6144K [0x00000007fa400000, 0x00000007fae00000, 0x00000007fae00000)

the space 10240K, 60% used [0x00000007fa400000, 0x00000007faa00030, 0x00000007faa00200, 0x00000007fae00000)

compacting perm gen total 21248K, used 2614K [0x00000007fae00000, 0x00000007fc2c0000, 0x0000000800000000)

the space 21248K, 12% used [0x00000007fae00000, 0x00000007fb08d840, 0x00000007fb08da00, 0x00000007fc2c0000)

No shared spaces configured.

這對組合就是中規中矩的，Eden發現4MB放不下了，觸發MinorGC,GC期間發現3個2MB全部無法放到Survivor裡面，所以只好通過擔保機制提前轉移到老年代中去。然後Eden放進了4MB的物件。

3.ParNew + Serial Old(-XX:+UseParNewGC)

[GC[ParNew: 6995K->282K(9216K), 0.0039460 secs] 6995K->6426K(19456K), 0.0039770 secs] [Times: user=0.01 sys=0.01, real=0.00 secs]

Heap

par new generation total 9216K, used 4708K [0x00000007f9a00000, 0x00000007fa400000, 0x00000007fa400000)

eden space 8192K, 54% used [0x00000007f9a00000, 0x00000007f9e527b0, 0x00000007fa200000)

from space 1024K, 27% used [0x00000007fa300000, 0x00000007fa346a50, 0x00000007fa400000)

to space 1024K, 0% used [0x00000007fa200000, 0x00000007fa200000, 0x00000007fa300000)

tenured generation total 10240K, used 6144K [0x00000007fa400000, 0x00000007fae00000, 0x00000007fae00000)

the space 10240K, 60% used [0x00000007fa400000, 0x00000007faa00030, 0x00000007faa00200, 0x00000007fae00000)

compacting perm gen total 21248K, used 2614K [0x00000007fae00000, 0x00000007fc2c0000, 0x0000000800000000)

the space 21248K, 12% used [0x00000007fae00000, 0x00000007fb08d840, 0x00000007fb08da00, 0x00000007fc2c0000)

No shared spaces configured.

跟上面的差不多。。。

4.Parallel Scavenge + Parallel Old(-XX:+UseParallelOldGC)