➜ Contents java -XX:+PrintCommandLineFlags -version
-XX:InitialHeapSize=536870912
-XX:MaxHeapSize=8589934592 -XX:+PrintCommandLineFlags
-XX:+UseCompressedClassPointers -XX:+UseCompressedOops
-XX:+UseParallelGC
java version "1.8.0_261"
Java(TM) SE Runtime Environment (build 1.8.0_261-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.261-b12, mixed mode)
UseParallelGC 即 Parallel Scavenge + Parallel Old,再查看详细信息
➜ Contents java -XX:+PrintGCDetails -version
java version "1.8.0_261"
Java(TM) SE Runtime Environment (build 1.8.0_261-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.261-b12, mixed mode)
Heap
PSYoungGen total 153088K, used 5263K [0x0000000715580000, 0x0000000720000000, 0x00000007c0000000)
eden space 131584K, 4% used [0x0000000715580000,0x0000000715aa3ef8,0x000000071d600000)
from space 21504K, 0% used [0x000000071eb00000,0x000000071eb00000,0x0000000720000000)
to space 21504K, 0% used [0x000000071d600000,0x000000071d600000,0x000000071eb00000)
ParOldGen total 349696K, used 0K [0x00000005c0000000, 0x00000005d5580000, 0x0000000715580000)
object space 349696K, 0% used [0x00000005c0000000,0x00000005c0000000,0x00000005d5580000)
Metaspace used 2245K, capacity 4480K, committed 4480K, reserved 1056768K
class space used 243K, capacity 384K, committed 384K, reserved 1048576K
从JDK7u4开始,就对 “-XX:+UseParallelGC” 默认的老年代收集器进行了改进,改进使得HotSpot VM在选择使用 “-XX:+UseParallelGC” 时,会默认开启 " -XX:+UseParallelOldGC “,也就是说默认的老年代收集器是 Parallel Old。 综上,JDK8中默认的选择是”-XX:+UseParallelGC",是 Parallel Scavenge + Parallel Old组合。
参考