jvm-3-jvm参数

来源：互联网发布：博客营销软件编辑：程序博客网时间：2024/05/17 03:09

跟踪参数

 1）-XX:+printGC   a： -verbose:gc    - [GC 4690 ->374K(15872K),0.0001606secs]      清除前堆大小 清除后  容量  2）-XX:+PrintGCDetails      打印GC详细信息     -XX:+PrintGCTimeStamps     打印GC发生的时间戳 3）指定GC位置     -Xloggc:log/gc.log  //当前目录下的log目录下的文件中 4) -XX:+PrintHeapAtGc     每次一次GC后都打印堆信息 5）-XX:+TraceClassLoading     监控类的加载  6）-XX:+PrintClassHistogram    -按下ctrl + Break 后 打印类的信息   -分别显示： 序号、实例数量、总大小、类型

###堆的分配参数

  1）-Xms20m -Xms5m       指定最大堆20m 最小堆5m  2）-Xmn15m    设置新生代大小15m  3）-XX:NewRatio    设置新生代（eden + 2 * s）和老年代（不包含永久区）的比值        如 4 则表示 新生代：老年代 1：4 即年轻代占堆的 1/5  4）-XX:SurvivorRato       设置两个Survivor区和eden的比    如 8 则表示 2个Survivor：eden = 2:8   5）-XX:+HeapDumpOnOutMemmoryError    oom时导出堆到文件  6）-XX:+HeapDumpPath        导出OOM的路径    如 -Xmx20m -Xms5m -XX:+HeapDumpOnOutOfMemoryError -XX:+HeapDumpPath=d:/a.dump  7) -XX:OnOutOfMemoryError     在OOM时，执行一个脚本     如-XX:OnOutOfMemoryEoor=D:/tools/jdk1.7_40/bin/printstack.bat %p        printstack.bat:D:/tools/jdk1.7_40/bin/jstack -F 1%

###永久区分配参数

   1)-XX:PermSize     永久区初始空间   2）-XX:MaxPermSize       永久区最大空间

###栈大小分配

   -Xss 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。

案例

  //JVM参数  -Xmx20m -Xms5m （最大堆内存20m，最小堆内存5m）public static void main(String[] args) {        byte[] bArr=new byte[1 * 1024 * 1024];  //1m内存         //byte[] bArr=new byte[4 * 1024 * 1024];  //4m内存        System.out.println(" heap is 1 M");        //System.gc();   //手动GC        System.out.print("Xmx = ");        System.out.print(Runtime.getRuntime().maxMemory()/1024.0/1024 + "M");        System.out.println();        System.out.print("free mem = ");        System.out.print(Runtime.getRuntime().freeMemory()/1024.0/1024 + "M");        System.out.println();        System.out.print("total mem =");        System.out.print(Runtime.getRuntime().totalMemory()/1024.0/1024 + "M");    }    //输出1    //heap is 1 M    //Xmx = 18.0M  最大可用内存    //free mem = 3.626312255859375M  空闲内存    //输出2  //开启4m内存    //heap is 4 M     //Xmx = 18.0M    //free mem = 4.5825958251953125M     //total mem =10.0M   增多    //输出3 开启4M 后 手动gc    //heap is 1 M    //Xmx = 18.0M    //free mem = 5.04815673828125M  空闲内存增多    //total mem =10.0M

//JVM参数 -Xmx20m -Xms20m -Xmn1m -XX:+PrintGCDetails public static void main(String[] args) {         byte [] bArr = null ;         for( int i = 0 ; i < 10 ; i ++) {             bArr=new byte[1 * 1024 * 1024];         }         //jvm参数 -Xmx20m -Xms20m -Xmn1m -XX:+PrintGCDetails         //输出：新生代GC频繁，对象较大，直接进入老年大，老年代内存大。    //[GC (Allocation Failure) [PSYoungGen: 512K->504K(1024K)] 512K->504K(19968K), 0.0009776 secs] [Times: user=0.00 sys=0.00, real=0.02 secs]    //[GC (Allocation Failure) [PSYoungGen: 1007K->504K(1024K)] 1007K->632K(19968K), 0.0015814 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]    //[GC (Allocation Failure) [PSYoungGen: 1008K->504K(1024K)] 1136K->786K(19968K), 0.0008114 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]    //[GC (Allocation Failure) [PSYoungGen: 1016K->504K(1024K)] 1298K->890K(19968K), 0.0008174 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]    //[GC (Allocation Failure) [PSYoungGen: 1016K->504K(1024K)] 7546K->7090K(19968K), 0.0015194 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]    //Heap    //Java HotSpot(TM) 64-Bit Server VM warning: NewSize (1536k) is greater than the MaxNewSize (1024k). A new max generation size of 1536k will be used.    //PSYoungGen      total 1024K, used 549K [0x00000000ffe80000, 0x0000000100000000, 0x0000000100000000)    //eden space 512K, 8% used [0x00000000ffe80000,0x00000000ffe8b400,0x00000000fff00000)    //from space 512K, 98% used [0x00000000fff00000,0x00000000fff7e010,0x00000000fff80000)    //to   space 512K, 0% used [0x00000000fff80000,0x00000000fff80000,0x0000000100000000)    //ParOldGen       total 18944K, used 10682K [0x00000000fec00000, 0x00000000ffe80000, 0x00000000ffe80000)    //object space 18944K, 56% used [0x00000000fec00000,0x00000000ff66e970,0x00000000ffe80000)    //Metaspace       used 3448K, capacity 4494K, committed 4864K, reserved 1056768K    //class space    used 380K, capacity 386K, committed 512K, reserved 1048576K    }//调整jvm参数-Xmx20m -Xms20m -Xmn15m（修改为15m） -XX:+PrintGCDetails//相同效果：-Xmx20m -Xms20m -XX:NewRatio=1（新生代老年代比）-XX:SurvivorRatio=2 -XX:+PrintGCDetails //输出：新生代大，新生代发生一次GC，对象在新生代积累后GC，进入老年代的内存占比少。[GC (Allocation Failure) [PSYoungGen: 12254K->1528K(13824K)] 12254K->1962K(18944K), 0.0032452 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] Heap PSYoungGen      total 13824K, used 2798K [0x00000000ff100000, 0x0000000100000000, 0x0000000100000000)  eden space 12288K, 10% used [0x00000000ff100000,0x00000000ff23d8a0,0x00000000ffd00000)  from space 1536K, 99% used [0x00000000ffd00000,0x00000000ffe7e040,0x00000000ffe80000)  to   space 1536K, 0% used [0x00000000ffe80000,0x00000000ffe80000,0x0000000100000000) ParOldGen       total 5120K, used 434K [0x00000000fec00000, 0x00000000ff100000, 0x00000000ff100000)  object space 5120K, 8% used [0x00000000fec00000,0x00000000fec6c8a0,0x00000000ff100000) Metaspace       used 3464K, capacity 4494K, committed 4864K, reserved 1056768K  class space    used 382K, capacity 386K, committed 512K, reserved 1048576K//JVM参数 -Xmx20m -Xms20m -Xmn7m（调整为7m）   -XX:SurvivorRatio=2（调整存活区比例） -XX:+PrintGCDetails//输出：调整新生代与存活区为1：1，GC相对增加[GC (Allocation Failure) [PSYoungGen: 3660K->971K(5632K)] 3660K->2003K(18944K), 0.0023069 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC (Allocation Failure) [PSYoungGen: 4121K->1528K(5632K)] 5153K->2856K(18944K), 0.0010785 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] [GC (Allocation Failure) [PSYoungGen: 4793K->1504K(5632K)] 6121K->2936K(18944K), 0.0007354 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] Heap PSYoungGen      total 5632K, used 4717K [0x00000000ff900000, 0x0000000100000000, 0x0000000100000000)  eden space 4096K, 78% used [0x00000000ff900000,0x00000000ffc23430,0x00000000ffd00000)  from space 1536K, 97% used [0x00000000ffd00000,0x00000000ffe78040,0x00000000ffe80000)  to   space 1536K, 0% used [0x00000000ffe80000,0x00000000ffe80000,0x0000000100000000) ParOldGen       total 13312K, used 1432K [0x00000000fec00000, 0x00000000ff900000, 0x00000000ff900000)  object space 13312K, 10% used [0x00000000fec00000,0x00000000fed66010,0x00000000ff900000) Metaspace       used 3454K, capacity 4494K, committed 4864K, reserved 1056768K  class space    used 380K, capacity 386K, committed 512K, reserved 1048576K

//JVM参数 -Xmx20m -Xms5m -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=d:/a.dump public static void main(String[] args) {        Vector vector=new Vector();         for( int i = 0 ; i < 30 ; i ++) {             vector.add(new byte[1 * 1024 * 1024]);         }    }//输出  jvm内存逃逸生成的内存dump文件分析    java.lang.OutOfMemoryError: Java heap spaceDumping heap to d:/a.dump ...Heap dump file created [16420586 bytes in 0.065 secs]Exception in thread "main" java.lang.OutOfMemoryError: Java heap space    at com.mybatis.datasources.common.jvm.TestJvm2.main(TestJvm2.java:13)

“`

阅读全文

0 0