-verbose:gc
-XX:+printGC
可以打印GC的简要信息
[GC 4790K->374K(15872K), 0.0001606 secs]
[GC 4790K->374K(15872K), 0.0001474 secs]
[GC 4790K->374K(15872K), 0.0001563 secs]
[GC 4790K->374K(15872K), 0.0001682 secs]
-XX:+PrintGCDetails 打印GC详细信息
例 [GC[DefNew: 4416K->0K(4928K), 0.0001897 secs] 4790K->374K(15872K), 0.0002232 secs] [Times: user= 0.00 sys= 0.00 , real= 0.00 secs]
-XX:+PrintGCTimeStamps 打印CG发生的时间戳,这个时间是相对于JVM启动时间的一个相对时间.
0.346 : [GC0. 346 : [DefNew: 4416K->512K(4928K), 0.0047316 secs] 4416K->1189K(15872K), 0.0050057 secs] [Times: user= 0.00 sys= 0.02 , real= 0.02 secs]
0.604 : [GC0. 604 : [DefNew: 4928K->512K(4928K), 0.0047917 secs] 5605K->2042K(15872K), 0.0049892 secs] [Times: user= 0.00 sys= 0.00 , real= 0.00 secs]
0.862 : [GC0. 862 : [DefNew: 4928K->512K(4928K), 0.0043302 secs] 6458K->2547K(15872K), 0.0045277 secs] [Times: user= 0.02 sys= 0.00 , real= 0.02 secs]
1.097 : [GC1. 097 : [DefNew: 4928K->511K(4928K), 0.0035988 secs] 6963K->2942K(15872K), 0.0037924 secs] [Times: user= 0.00 sys= 0.02 , real= 0.02 secs]
1.332 : [GC1. 332 : [DefNew: 4927K->511K(4928K), 0.0036309 secs] 7358K->3295K(15872K), 0.0038239 secs] [Times: user= 0.01 sys= 0.00 , real= 0.01 secs]
1.501 : [Full GC1. 501 : [Tenured: 2783K->2593K(10944K), 0.0277544 secs] 6493K->2593K(15872K), [Perm : 4095K->4095K(4096K)], 0.0279980 secs] [Times: user= 0.03 sys= 0.00 , real= 0.03 secs]
1.529 : [Full GC1. 529 : [Tenured: 2593K->2593K(10944K), 0.0228733 secs] 2593K->2593K(15936K), [Perm : 4095K->4095K(4096K)], 0.0229870 secs] [Times: user= 0.02 sys= 0.00 , real= 0.02 secs]
1.555 : [Full GC1. 555 : [Tenured: 2593K->999K(10944K), 0.0235103 secs] 2678K->999K(15936K), [Perm : 4095K->4095K(4096K)], 0.0236762 secs] [Times: user= 0.02 sys= 0.00 , real= 0.02 secs]
1.579 : [Full GC1. 579 : [Tenured: 999K->983K(10944K), 0.0265414 secs] 1045K->983K(15936K), [Perm : 4095K->4092K(4096K)], 0.0267126 secs] [Times: user= 0.01 sys= 0.00 , real= 0.03 secs]
Heap
def new generation total 4992K, used 175K [ 0x26720000 , 0x26c80000 , 0x2bc70000 )
eden space 4480K, 3 % used [ 0x26720000 , 0x2674bd48 , 0x26b80000 )
from space 512K, 0 % used [ 0x26b80000 , 0x26b80000 , 0x26c00000 )
to space 512K, 0 % used [ 0x26c00000 , 0x26c00000 , 0x26c80000 )
tenured generation total 10944K, used 983K [ 0x2bc70000 , 0x2c720000 , 0x36720000 )
the space 10944K, 8 % used [ 0x2bc70000 , 0x2bd65ce0 , 0x2bd65e00 , 0x2c720000 )
compacting perm gen total 4096K, used 4094K [ 0x36720000 , 0x36b20000 , 0x36b20000 )
the space 4096K, 99 % used [ 0x36720000 , 0x36b1f948 , 0x36b1fa00 , 0x36b20000 )
ro space 10240K, 44 % used [ 0x36b20000 , 0x36f97e30 , 0x36f98000 , 0x37520000 )
rw space 12288K, 52 % used [ 0x37520000 , 0x37b6eb58 , 0x37b6ec00 , 0x38120000 )
-XX:+PrintGCDateStamps 打印CG发生的时间戳,是一个阅读性好的,普通的日期时间.
java -jar -XX:+PrintGCDateStamps -XX:+PrintGCDetails -verbose:gc yed.jar
2011 - 05 -11T17: 49 : 43.959 + 0800 : [GC [PSYoungGen: 15360K->2464K(17856K)] 15360K->8417K(58688K), 0.0260480 secs] [Times: user= 0.05 sys= 0.00 , real= 0.02 secs]
2011 - 05 -11T17: 49 : 44.612 + 0800 : [GC [PSYoungGen: 17824K->2484K(33216K)] 23777K->10471K(74048K), 0.0156130 secs] [Times: user= 0.03 sys= 0.00 , real= 0.02 secs]
2011 - 05 -11T17: 49 : 44.724 + 0800 : [GC [PSYoungGen: 33204K->2466K(33216K)] 41191K->10509K(74048K), 0.0088430 secs] [Times: user= 0.02 sys= 0.00 , real= 0.01 secs]
2011 - 05 -11T17: 49 : 44.771 + 0800 : [GC [PSYoungGen: 33186K->2466K(63936K)] 41229K->10509K(104768K), 0.0069690 secs] [Times: user= 0.02 sys= 0.00 , real= 0.01 secs]
2011 - 05 -11T17: 49 : 44.911 + 0800 : [GC [PSYoungGen: 63906K->2482K(63936K)] 71949K->10525K(104768K), 0.0071580 secs] [Times: user= 0.02 sys= 0.00 , real= 0.01 secs]
2011 - 05 -11T17: 49 : 47.282 + 0800 : [GC [PSYoungGen: 63922K->8765K(130048K)] 71965K->16807K(170880K), 0.0409860 secs] [Times: user= 0.07 sys= 0.01 , real= 0.04 secs]
-XX:+PrintGCDetails的输出
Heap 12288K+ 1536K [低边界 当前边界 最高边界]
def new generation total 13824K, used 11223K [ 0x27e80000 , 0x28d80000 , 0x28d80000 ) （ 0x28d80000 - 0x27e80000 )/ 1024 / 1024 =15M
eden space 12288K, 91 % used [ 0x27e80000 , 0x28975f20 , 0x28a80000 )
from space 1536K, 0 % used [ 0x28a80000 , 0x28a80000 , 0x28c00000 )
to space 1536K, 0 % used [ 0x28c00000 , 0x28c00000 , 0x28d80000 )
tenured generation total 5120K, used 0K [ 0x28d80000 , 0x29280000 , 0x34680000 )
the space 5120K, 0 % used [ 0x28d80000 , 0x28d80000 , 0x28d80200 , 0x29280000 )
compacting perm gen total 12288K, used 142K [ 0x34680000 , 0x35280000 , 0x38680000 )
the space 12288K, 1 % used [ 0x34680000 , 0x346a3a90 , 0x346a3c00 , 0x35280000 )
ro space 10240K, 44 % used [ 0x38680000 , 0x38af73f0 , 0x38af7400 , 0x39080000 )
rw space 12288K, 52 % used [ 0x39080000 , 0x396cdd28 , 0x396cde00 , 0x39c80000 )
-Xloggc:log/gc.log 指定GC log的位置，以文件输出 帮助开发人员分析问题
目录可以是一个相对当前目录的相对地址，但是目录要存在，否则没有输出文件.
