android 常用JVM配置参数

Trace跟踪参数-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-XX:+PrintGCTimeStamps打印CG发生的时间戳例[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:+PrintGCDetails的输出Heapdef new generation   total 13824K, used 11223K [0x27e80000, 0x28d80000, 0x28d80000)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-XX:+PrintHeapAtGC每次一次GC后，都打印堆信息{Heap before GC invocations=0 (full 0): def new generation   total 3072K, used 2752K [0x33c80000, 0x33fd0000, 0x33fd0000)eden space 2752K, 100% used [0x33c80000, 0x33f30000, 0x33f30000)from space 320K,   0% used [0x33f30000, 0x33f30000, 0x33f80000)to   space 320K,   0% used [0x33f80000, 0x33f80000, 0x33fd0000)tenured generation   total 6848K, used 0K [0x33fd0000, 0x34680000, 0x34680000)the space 6848K,   0% used [0x33fd0000, 0x33fd0000, 0x33fd0200, 0x34680000)compacting perm gen  total 12288K, used 143K [0x34680000, 0x35280000, 0x38680000)the space 12288K,   1% used [0x34680000, 0x346a3c58, 0x346a3e00, 0x35280000)ro space 10240K,  44% used [0x38680000, 0x38af73f0, 0x38af7400, 0x39080000)rw space 12288K,  52% used [0x39080000, 0x396cdd28, 0x396cde00, 0x39c80000)[GC[DefNew: 2752K->320K(3072K), 0.0014296 secs] 2752K->377K(9920K), 0.0014604 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]Heap after GC invocations=1 (full 0):def new generation   total 3072K, used 320K [0x33c80000, 0x33fd0000, 0x33fd0000)eden space 2752K,   0% used [0x33c80000, 0x33c80000, 0x33f30000)from space 320K, 100% used [0x33f80000, 0x33fd0000, 0x33fd0000)to   space 320K,   0% used [0x33f30000, 0x33f30000, 0x33f80000)tenured generation   total 6848K, used 57K [0x33fd0000, 0x34680000, 0x34680000)the space 6848K,   0% used [0x33fd0000, 0x33fde458, 0x33fde600, 0x34680000)compacting perm gen  total 12288K, used 143K [0x34680000, 0x35280000, 0x38680000)the space 12288K,   1% used [0x34680000, 0x346a3c58, 0x346a3e00, 0x35280000)ro space 10240K,  44% used [0x38680000, 0x38af73f0, 0x38af7400, 0x39080000)rw space 12288K,  52% used [0x39080000, 0x396cdd28, 0x396cde00, 0x39c80000)}-XX:+TraceClassLoading监控类的加载[Loaded java.lang.Object from shared objects file][Loaded java.io.Serializable from shared objects file][Loaded java.lang.Comparable from shared objects file][Loaded java.lang.CharSequence from shared objects file][Loaded java.lang.String from shared objects file][Loaded java.lang.reflect.GenericDeclaration from shared objects file][Loaded java.lang.reflect.Type from shared objects file]跟踪调试的时候 那些类被加载出来-XX:+PrintClassHistogram按下Ctrl+Break后，打印类的信息：num     #instances         #bytes  class name----------------------------------------------   1:        890617      470266000  [B   2:        890643       21375432  java.util.HashMap$Node   3:        890608       14249728  java.lang.Long   4:            13        8389712  [Ljava.util.HashMap$Node;   5:          2062         371680  [C   6:           463          41904  java.lang.Class分别显示：序号、实例数量、总大小、类型堆的分配参数Xmx –Xms指定最大堆和最小堆VM options: -Xmx20m -Xms5m 运行代码：    public static void main(String[] args)  {        System.out.print("Xmx=");        System.out.println(Runtime.getRuntime().maxMemory()/1024.0/1024+"M");        System.out.print("free mem=");        System.out.println(Runtime.getRuntime().freeMemory()/1024.0/1024+"M");        System.out.print("total mem=");        System.out.println(Runtime.getRuntime().totalMemory()/1024.0/1024+"M");    }结果：Xmx=18.0Mfree mem=4.660301208496094Mtotal mem=5.5M    public static void main(String[] args)  {        byte[] b= new byte[4 * 1024 * 1024];        System.out.print("Xmx=");        System.out.println(Runtime.getRuntime().maxMemory()/1024.0/1024+"M");        System.out.print("free mem=");        System.out.println(Runtime.getRuntime().freeMemory()/1024.0/1024+"M");        System.out.print("total mem=");        System.out.println(Runtime.getRuntime().totalMemory()/1024.0/1024+"M");    }结果：Xmx=18.0Mfree mem=5.074928283691406Mtotal mem=10.0M总内存变多    public static void main(String[] args)  {        System.gc();        System.out.print("Xmx=");        System.out.println(Runtime.getRuntime().maxMemory()/1024.0/1024+"M");        System.out.print("free mem=");        System.out.println(Runtime.getRuntime().freeMemory()/1024.0/1024+"M");        System.out.print("total mem=");        System.out.println(Runtime.getRuntime().totalMemory()/1024.0/1024+"M");    }结果：Xmx=18.0Mfree mem=5.9815826416015625Mtotal mem=6.5M

空闲内存变多

-Xmn
设置新生代大小
-XX:NewRatio
新生代（eden+2*s）和老年代（不包含永久区）的比值
4 表示新生代:老年代=1:4，即年轻代占堆的1/5
-XX:SurvivorRatio
设置两个Survivor区和eden的比
8表示两个Survivor :eden=2:8，即一个Survivor占年轻代的1/10

    public static void main(String[] args) {        byte[] b=null;        for(int i=0;i<10;i++)            b=new byte[1*1024*1024];    }VM options: -Xmx20m -Xms20m -Xmn3m -XX:+PrintGCDetails输出：Heap PSYoungGen      total 2560K, used 1490K [0x00000007bfd00000, 0x00000007c0000000, 0x00000007c0000000)  eden space 2048K, 72% used [0x00000007bfd00000,0x00000007bfe748a8,0x00000007bff00000)  from space 512K, 0% used [0x00000007bff80000,0x00000007bff80000,0x00000007c0000000)  to   space 512K, 0% used [0x00000007bff00000,0x00000007bff00000,0x00000007bff80000) ParOldGen       total 17408K, used 10240K [0x00000007bec00000, 0x00000007bfd00000, 0x00000007bfd00000)  object space 17408K, 58% used [0x00000007bec00000,0x00000007bf6000a0,0x00000007bfd00000) Metaspace       used 3054K, capacity 4496K, committed 4864K, reserved 1056768K  class space    used 334K, capacity 388K, committed 512K, reserved 1048576K

没有触发GC
全部分配在老年代

VM options: -Xmx20m -Xms20m -Xmn15m -XX:+PrintGCDetails输出：Heap PSYoungGen      total 13824K, used 11966K [0x00000007bf100000, 0x00000007c0000000, 0x00000007c0000000)  eden space 12288K, 97% used [0x00000007bf100000,0x00000007bfcaf8d0,0x00000007bfd00000)  from space 1536K, 0% used [0x00000007bfe80000,0x00000007bfe80000,0x00000007c0000000)  to   space 1536K, 0% used [0x00000007bfd00000,0x00000007bfd00000,0x00000007bfe80000) ParOldGen       total 5120K, used 0K [0x00000007bec00000, 0x00000007bf100000, 0x00000007bf100000)  object space 5120K, 0% used [0x00000007bec00000,0x00000007bec00000,0x00000007bf100000) Metaspace       used 3051K, capacity 4496K, committed 4864K, reserved 1056768K  class space    used 334K, capacity 388K, committed 512K, reserved 1048576K

没有触发GC
全部分配在eden
老年代没有使用

VM options: -Xmx20m -Xms20m -Xmn15m -XX:+PrintGCDetails输出[GC (Allocation Failure) [PSYoungGen: 5797K->496K(6656K)] 6861K->2604K(19968K), 0.0011469 secs] [Times: user=0.01 sys=0.00, real=0.00 secs] Heap PSYoungGen      total 6656K, used 1622K [0x00000007bf900000, 0x00000007c0000000, 0x00000007c0000000)  eden space 6144K, 18% used [0x00000007bf900000,0x00000007bfa19ab8,0x00000007bff00000)  from space 512K, 96% used [0x00000007bff80000,0x00000007bfffc010,0x00000007c0000000)  to   space 512K, 0% used [0x00000007bff00000,0x00000007bff00000,0x00000007bff80000) ParOldGen       total 13312K, used 2108K [0x00000007bec00000, 0x00000007bf900000, 0x00000007bf900000)  object space 13312K, 15% used [0x00000007bec00000,0x00000007bee0f030,0x00000007bf900000) Metaspace       used 2947K, capacity 4496K, committed 4864K, reserved 1056768K  class space    used 325K, capacity 388K, committed 512K, reserved 1048576K进行了1次新生代GCs0 s1 太小需要老年代担保VM options: -Xmx20m -Xms20m -Xmn6m -XX:SurvivorRatio=2 -XX:+PrintGCDetails[GC (Allocation Failure) [PSYoungGen: 2357K->1520K(4608K)] 2357K->1560K(18944K), 0.0010973 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC (Allocation Failure) [PSYoungGen: 3658K->1504K(4608K)] 3698K->1552K(18944K), 0.0009730 secs] [Times: user=0.01 sys=0.00, real=0.00 secs] [GC (Allocation Failure) [PSYoungGen: 3621K->1504K(4608K)] 3669K->1576K(18944K), 0.0004732 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC (Allocation Failure) [PSYoungGen: 3604K->1520K(4608K)] 3676K->1608K(18944K), 0.0004172 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC (Allocation Failure) [PSYoungGen: 3623K->1520K(4608K)] 3711K->1616K(18944K), 0.0004710 secs] [Times: user=0.01 sys=0.00, real=0.01 secs] Heap PSYoungGen      total 4608K, used 2619K [0x00000007bfa00000, 0x00000007c0000000, 0x00000007c0000000)  eden space 3072K, 35% used [0x00000007bfa00000,0x00000007bfb12e48,0x00000007bfd00000)  from space 1536K, 98% used [0x00000007bfd00000,0x00000007bfe7c020,0x00000007bfe80000)  to   space 1536K, 0% used [0x00000007bfe80000,0x00000007bfe80000,0x00000007c0000000) ParOldGen       total 14336K, used 96K [0x00000007bec00000, 0x00000007bfa00000, 0x00000007bfa00000)  object space 14336K, 0% used [0x00000007bec00000,0x00000007bec18000,0x00000007bfa00000) Metaspace       used 2929K, capacity 4496K, committed 4864K, reserved 1056768K  class space    used 319K, capacity 388K, committed 512K, reserved 1048576K进行了5次新生代GCs0 s1 增大-XX:+HeapDumpOnOutOfMemoryErrorOOM时导出堆到文件-XX:+HeapDumpPath导出OOM的路径-XX:OnOutOfMemoryError在OOM时，执行一个脚本"-XX:OnOutOfMemoryError=D:/tools/jdk1.7_40/bin/printstack.bat %p“当程序OOM时，在D:/a.txt中将会生成线程的dump可以在OOM时，发送邮件，甚至是重启程序总结根据实际事情调整新生代和幸存代的大小官方推荐新生代占堆的3/8幸存代占新生代的1/10在OOM时，记得Dump出堆，确保可以排查线程永久区分配参数-XX:PermSize -XX:MaxPermSize

设置永久区的初始空间和最大空间
他们表示，一个系统可以容纳多少个类型
使用CGLIB等库的时候，可能会产生大量的类，这些类，有可能撑爆永久区导致OOM

for(int i=0;i<100000;i++){    CglibBean bean = new CglibBean("geym.jvm.ch3.perm.bean"+i,new HashMap());}

不断产生新的类

打开堆的Dump
堆空间实际占用非常少
但是永久区溢出一样抛出OOM

如果堆空间没有用完也抛出了OOM，有可能是永久区导致的
栈大小分配
通常只有几百K
决定了函数调用的深度
每个线程都有独立的栈空间
局部变量、参数分配在栈上

    private static int count=0;    public static void recursion(long a,long b,long c){        long e=1,f=2,g=3,h=4,i=5,k=6,q=7,x=8,y=9,z=10;        count++;        recursion(a,b,c);    }    public static void main(String args[]){        try{            recursion(0L,0L,0L);        }catch(Throwable e){            System.out.println("deep of calling = "+count);            e.printStackTrace();        }    }VM options: -Xss160Kdeep of calling = 235java.lang.StackOverflowError...VM options: -Xss280Kdeep of calling = 662java.lang.StackOverflowError

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