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Java虚拟机 5：Java垃圾回收（GC）机制详解(四)
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Serial Old收集器串行回收 |
该选项可以手动指定Serial收集器+Serial Old收集器组合执行内存回收 |
| -XX:+UseParNewGC |
ParNew收集器并行回收 |
Serial Old收集器串行回收 |
该选项可以手动指定ParNew收集器+Serilal Old组合执行内存回收 |
| -XX:+UseParallelGC |
Parallel收集器并行回收 |
Serial Old收集器串行回收 |
该选项可以手动指定Parallel收集器+Serial Old收集器组合执行内存回收 |
| -XX:+UseParallelOldGC |
Parallel收集器并行回收 |
Parallel Old收集器并行回收 |
该选项可以手动指定Parallel收集器+Parallel Old收集器组合执行内存回收 |
| -XX:+UseConcMarkSweepGC |
ParNew收集器并行回收 |
缺省使用CMS收集器并发回收，备用采用Serial Old收集器串行回收 |
该选项可以手动指定ParNew收集器+CMS收集器+Serial Old收集器组合执行内存回收。优先使用ParNew收集器+CMS收集器的组合，当出现ConcurrentMode Fail或者Promotion Failed时，则采用ParNew收集器+Serial Old收集器的组合 |
| -XX:+UseConcMarkSweepGC-XX:-UseParNewGC |
Serial收集器串行回收 |
| -XX:+UseG1GC |
G1收集器并发、并行执行内存回收 |
暂无 |
GC日志
每种收集器的日志形式都是由它们自身的实现所决定的，换言之，每种收集器的日志格式都可以不一样。不过虚拟机为了方便用户阅读，将各个收集器的日志都维持了一定的共性，就以最前面的对象间相互引用的那个类ReferenceCountingGC的代码为例：
虚拟机参数为“-XX:+PrintGCDetails -XX:+UseSerialGC”，使用Serial+Serial Old组合进行垃圾回收的日志
[GC [DefNew: 310K->194K(2368K), 0.0269163 secs] 310K->194K(7680K), 0.0269513 secs] [Times: user=0.00 sys=0.00, real=0.03 secs]
[GC [DefNew: 2242K->0K(2368K), 0.0018814 secs] 2242K->2241K(7680K), 0.0019172 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System) [Tenured: 2241K->193K(5312K), 0.0056517 secs] 4289K->193K(7680K), [Perm : 2950K->2950K(21248K)], 0.0057094 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
Heap
def new generation total 2432K, used 43K [0x00000000052a0000, 0x0000000005540000, 0x0000000006ea0000)
eden space 2176K, 2% used [0x00000000052a0000, 0x00000000052aaeb8, 0x00000000054c0000)
from space 256K, 0% used [0x00000000054c0000, 0x00000000054c0000, 0x0000000005500000)
to space 256K, 0% used [0x0000000005500000, 0x0000000005500000, 0x0000000005540000)
tenured generation total 5312K, used 193K [0x0000000006ea0000, 0x00000000073d0000, 0x000000000a6a0000)
the space 5312K, 3% used [0x0000000006ea0000, 0x0000000006ed0730, 0x0000000006ed0800, 0x00000000073d0000)
compacting perm gen total 21248K, used 2982K [0x000000000a6a0000, 0x000000000bb60000, 0x000000000faa0000)
the space 21248K, 14% used [0x000000000a6a0000, 0x000000000a989980, 0x000000000a989a00, 0x000000000bb60000)
No shared spaces configured.
虚拟机参数为“-XX:+PrintGCDetails -XX:+UseParNewGC”，使用ParNew+Serial Old组合进行垃圾回收的日志
[GC [ParNew: 310K->205K(2368K), 0.0006664 secs] 310K->205K(7680K), 0.0007043 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC [ParNew: 2253K->31K(2368K), 0.0032525 secs] 2253K->2295K(7680K), 0.0032911 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[Full GC (System) [Tenured: 2264K->194K(5312K), 0.0054415 secs] 4343K->194K(7680K), [Perm : 2950K->2950K(21248K)], 0.0055105 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
Heap
par new generation total 2432K, used 43K [0x0000000005550000, 0x00000000057f0000, 0x0000000007150000)
eden space 2176K, 2% used [0x0000000005550000, 0x000000000555aeb8, 0x0000000005770000)
from space 256K, 0% used [0x0000000005770000, 0x0000000005770000, 0x00000000057b0000)
to space 256K, 0% used [0x00000000057b0000, 0x00000000057b0000, 0x00000000057f0000)
tenured generation total 5312K, used 194K [0x0000000007150000, 0x0000000007680000, 0x000000000a950000)
the space 5312K, 3% used [0x0000000007150000, |