JVM参数和jvm.log

参数说明:

-Xms    初始堆大小

-Xmx    最大堆大小

-Xmn    年轻代大小 eden + 2 survivor space

-XX:SurvivorRatio=8     Eden区与Survivor区的大小比值

-XX:PermSize    设置持久代(perm gen)初始值

-XX:MaxPermSize    设置持久代最大值

-Xss    每个线程的堆栈大小

-XX:CMSInitiatingOccupancyFraction=    年老代使用空间比达到这个值时开始cms gc



-XX:+PrintGCApplicationStoppedTime    打印垃圾回收期间程序暂停的时间

-XX:+PrintGCApplicationConcurrentTime    打印每次垃圾回收前,程序未中断的执行时间

-XX:+PrintHeapAtGC    打印GC前后的详细堆栈信息

 

测试配置:

-Xms1000m -Xmx1000m -Xmn400m 

-XX:PermSize=128m -XX:MaxPermSize=128m

-Xss512k

-XX:+UseConcMarkSweepGC -XX:+UseParNewGC 

-XX:SurvivorRatio=8 

-XX:+PrintGCApplicationStoppedTime -XX:+PrintGCApplicationConcurrentTime -XX:+PrintHeapAtGC 

-XX:+PrintGCDetails -XX:+PrintGCDateStamps -Xloggc:/data/lxx.jvm

-XX:CMSInitiatingOccupancyFraction=80

 

 

Young GC:
    日志:
        2015-01-15T16:04:24.237+0800: 1691.665: [GC 1691.665: [ParNew: 350110K->22406K(368640K), 0.0055010 secs] 430492K->105988K(983040K), 0.0055690 secs] [Times: user=0.02 sys=0.00, real=0.01 secs]
    日志说明:

2015-01-15T16:04:24.237+0800: 1691.665: [

        GC 1691.665: [      # (Young GC) 时间戳

            ParNew:                     # ParNew(使用ParNew作为年轻代的垃圾回收期)

            350110K->22406K(368640K),   # 年轻代 回收前大小->回收后大小(年轻代容量)

            0.0055010 secs              # 回收时间

        ] 

        430492K->105988K(983040K),      # 堆 回收前大小->回收后大小(堆容量)

        0.0055690 secs                  # 回收时间

    ] [

        Times: user=0.02 sys=0.00, real=0.01 secs   # Young GC用户耗时, Young GC系统耗时, Young GC实际耗时

    ] 

    内存容量

        年轻代: 368640K(360M) = 400M / (8 + 1 + 1) * (8 + 1) (始终闲置着40M)

        堆:     983040K(960M) = 1000M - 40M

    内存变化:

        年轻代: 368640K(360M)   350110K - 22406K  = 327704K

        堆:     983040K(960M)   430492K - 105988K = 324504K

                                327704K - 324504K = 3200K 被移动到了Old Gen

 

Full GC
    日志:
        2015-01-15T16:29:53.894+0800: 3221.322: [Full GC 3221.322: [CMS: 614343K->614234K(614400K), 0.4258390 secs] 982961K->973059K(983040K), [CMS Perm : 121449K->121449K(131072K)], 0.4259380 secs] [Times: user=0.43 sys=0.00, real=0.42 secs]
        2015-01-15T16:28:49.218+0800: 3156.645: [Full GC (System) 3156.645: [CMS2015-01-15T16:28:49.377+0800: 3156.805: [CMS-concurrent-mark: 0.165/0.166 secs] [Times: user=0.19 sys=0.00, real=0.17 secs]
    日志说明:
            

Full GC (System)    # 显式调用System.gc产生的



    2015-01-15T16:29:53.894+0800: 3221.322: [

        Full GC 3221.322: [     # (Full GC) 时间戳

            CMS: 

            614343K->614234K(614400K),  # old区 回收前大小->回收后大小(old区容量)

            0.4258390 secs              # 回收时间

        ] 

        982961K->973059K(983040K),  [   # 堆 回收前大小->回收后大小(堆容量)

            CMS Perm : 121449K->121449K(131072K)    # Perm区 回收前大小->回收后大小(Perm区容量)

        ], 0.4259380 secs               # 回收时间

    ] [

        Times: user=0.43 sys=0.00, real=0.42 secs

    ] 

    内存容量

        Old区:  614400K(600M) = 1000M - 400M = 960M - 360M

        堆:     983040K(960M)

    内存变化:

        Old区:  614400K(600M)   614343K - 614234K = 109K

        堆:     983040K(960M)   982961K - 973059K = 9902K

 

ParNew (promotion failed)
    发生在新生代晋升老年代时,老年代空间不够或连续空间不够却还没达到old区的触发值,引发Full Gc.
    2015-01-15T16:26:07.003+0800: 2994.431: [GC 2994.431: [ParNew (promotion failed): 351815K->349784K(368640K), 0.0095780 secs]2994.441: [CMS2015-01-15T16:26:07.074+0800: 2994.502: [CMS-concurrent-mark: 1.043/1.166 secs] [Times: user=4.25 sys=0.03, real=1.16 secs]

concurrent mode failure
    发生在CMS GC 运行过程中,老年代空间不足，引发MSC
    2015-01-15T16:26:07.003+0800: 2994.431: [GC 2994.431: [ParNew (promotion failed): 351815K->349784K(368640K), 0.0095780 secs]2994.441: [CMS2015-01-15T16:26:07.074+0800: 2994.502: [CMS-concurrent-mark: 1.043/1.166 secs] [Times: user=4.25 sys=0.03, real=1.16 secs]
    (concurrent mode failure): 614155K->614338K(614400K), 0.5011370 secs] 960545K->632140K(983040K), [CMS Perm : 121434K->121434K(131072K)], 0.5108440 secs] [Times: user=0.52 sys=0.00, real=0.51 secs]

 

[参考] http://hot66hot.iteye.com/blog/2075819