java -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -version
-XX:InitialHeapSize=132304640 -XX:MaxHeapSize=2116874240 -XX:ParallelGCThreads=4 -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseCompressedOops -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC
java version "1.7.0_01"
Java(TM) SE Runtime Environment (build 1.7.0_01-b08)
Java HotSpot(TM) 64-Bit Server VM (build 21.1-b02, mixed mode)
Heap
PSYoungGen total 37696K, used 1293K [0x00000007d5eb0000, 0x00000007d88c0000, 0x0000000800000000)
eden space 32320K, 4% used [0x00000007d5eb0000,0x00000007d5ff3408,0x00000007d7e40000)
from space 5376K, 0% used [0x00000007d8380000,0x00000007d8380000,0x00000007d88c0000)
to space 5376K, 0% used [0x00000007d7e40000,0x00000007d7e40000,0x00000007d8380000)
PSOldGen total 86144K, used 0K [0x0000000781c00000, 0x0000000787020000, 0x00000007d5eb0000)
object space 86144K, 0% used [0x0000000781c00000,0x0000000781c00000,0x0000000787020000)
PSPermGen total 21248K, used 2032K [0x000000077ca00000, 0x000000077dec0000, 0x0000000781c00000)
object space 21248K, 9% used [0x000000077ca00000,0x000000077cbfc288,0x000000077dec0000)
You don't need to enable experimental options to turn on the G1 collector any more, though:
> java -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseG1GC -version
-XX:InitialHeapSize=132304640 -XX:MaxHeapSize=2116874240 -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseCompressedOops -XX:+UseG1GC -XX:-UseLargePagesIndividualAllocation
java version "1.7.0_01"
Java(TM) SE Runtime Environment (build 1.7.0_01-b08)
Java HotSpot(TM) 64-Bit Server VM (build 21.1-b02, mixed mode)
Heap
garbage-first heap total 130048K, used 0K [0x000000077ca00000, 0x0000000784900000, 0x00000007fae00000)
region size 1024K, 1 young (1024K), 0 survivors (0K)
compacting perm gen total 20480K, used 2032K [0x00000007fae00000, 0x00000007fc200000, 0x0000000800000000)
the space 20480K, 9% used [0x00000007fae00000, 0x00000007faffc288, 0x00000007faffc400, 0x00000007fc200000)
用此方法查看我机器上的jdk7u5,发现默认默认GC还是原来的CMS,并非G1.
Oracle官方文档:
http://docs.oracle.com/javase/7/docs/technotes/guides/vm/G1.html
看来java7u4及其以后版本只是完全支持G1回收器,而非默认就是G1,如果需要使用G1还是需要添加参数 -XX:+UseG1GC
