JVM常用参数配置

今天药忘吃喽~ 2024-04-18 20:29 84阅读 0赞

> 本文涉及：gc、堆、栈、永久区、元数据区的常用参数

**GC基本参数**

打印gc简要信息：-XX:+PrintGC

[GC (System.gc())  198247K->197248K(261632K), 0.0178572 secs]	
    [Full GC (System.gc())  197248K->197184K(261632K), 0.0842625 secs]

上方结果描述：

分别是GC和Full GC释放的空间以及所用的时间

打印gc的详细信息 : -XX:+PrintGCDetails

Heap	
     PSYoungGen      total 18944K, used 164K [0x00000000eb200000, 0x00000000ec700000, 0x0000000100000000)	
      eden space 16384K, 1% used [0x00000000eb200000,0x00000000eb2290d0,0x00000000ec200000)	
      from space 2560K, 0% used [0x00000000ec200000,0x00000000ec200000,0x00000000ec480000)	
      to   space 2560K, 0% used [0x00000000ec480000,0x00000000ec480000,0x00000000ec700000)	
     ParOldGen       total 292352K, used 246336K [0x00000000c1600000, 0x00000000d3380000, 0x00000000eb200000)	
      object space 292352K, 84% used [0x00000000c1600000,0x00000000d0690290,0x00000000d3380000)	
     Metaspace       used 2866K, capacity 4486K, committed 4864K, reserved 1056768K	
      class space    used 308K, capacity 386K, committed 512K, reserved 1048576K

上方结果描述：

*  第2行：新生代总内存和已用内存
 *  第3、4、5行：新生代各个区总内存和已用内存，这里eden:from:to的比例为8:1:1
 *  第6行：老年代总内存和已用内存

指定gc日志的位置： -Xloggc:D:\\appLog\\app.log

打印gc前后的堆栈信息： -XX:+PrintHeapAtGC

{Heap before GC invocations=1 (full 0):	
     PSYoungGen      total 18944K, used 1639K [0x00000000eb200000, 0x00000000ec700000, 0x0000000100000000)	
      eden space 16384K, 10% used [0x00000000eb200000,0x00000000eb399c28,0x00000000ec200000)	
      from space 2560K, 0% used [0x00000000ec480000,0x00000000ec480000,0x00000000ec700000)	
      to   space 2560K, 0% used [0x00000000ec200000,0x00000000ec200000,0x00000000ec480000)	
     ParOldGen       total 491008K, used 442368K [0x00000000c1600000, 0x00000000df580000, 0x00000000eb200000)	
      object space 491008K, 90% used [0x00000000c1600000,0x00000000dc600090,0x00000000df580000)	
     Metaspace       used 2860K, capacity 4486K, committed 4864K, reserved 1056768K	
      class space    used 307K, capacity 386K, committed 512K, reserved 1048576K	
     [Full GC (System.gc())  443064K->442944K(509952K), 0.1634157 secs]	
    Heap after GC invocations=1 (full 0):	
     PSYoungGen      total 18944K, used 664K [0x00000000eb200000, 0x00000000ec700000, 0x0000000100000000)	
      eden space 16384K, 0% used [0x00000000eb200000,0x00000000eb200000,0x00000000ec200000)	
      from space 2560K, 25% used [0x00000000ec200000,0x00000000ec2a6030,0x00000000ec480000)	
      to   space 2560K, 0% used [0x00000000ec480000,0x00000000ec480000,0x00000000ec700000)	
     ParOldGen       total 491008K, used 442376K [0x00000000c1600000, 0x00000000df580000, 0x00000000eb200000)	
      object space 491008K, 90% used [0x00000000c1600000,0x00000000dc602090,0x00000000df580000)	
     Metaspace       used 2860K, capacity 4486K, committed 4864K, reserved 1056768K	
      class space    used 307K, capacity 386K, committed 512K, reserved 1048576K	
    }

上方结果描述：

*  1-9行是gc之前的新生代、老年代和元空间（这是jdk8更新的，之前是永久区）信息
 *  第10行打印了一次full gc的相关信息

监控类的加载：-XX:+TraceClassLoadingPreorder

[Opened C:\Program Files (x86)\Java\jdk1.8.0_181\jre\lib\rt.jar]	
    [Loaded java.lang.Object from C:\Program Files (x86)\Java\jdk1.8.0_181\jre\lib\rt.jar]	
    [Loaded java.io.Serializable from C:\Program Files (x86)\Java\jdk1.8.0_181\jre\lib\rt.jar]	
    [Loaded java.lang.Comparable from C:\Program Files (x86)\Java\jdk1.8.0_181\jre\lib\rt.jar]	
    [Loaded java.lang.CharSequence from C:\Program Files (x86)\Java\jdk1.8.0_181\jre\lib\rt.jar]	
    [Loaded java.lang.String from C:\Program Files (x86)\Java\jdk1.8.0_181\jre\lib\rt.jar]	
    [Loaded java.lang.reflect.AnnotatedElement from C:\Program Files (x86)\Java\jdk1.8.0_181\jre\lib\rt.jar]	
    [Loaded java.lang.reflect.GenericDeclaration from C:\Program Files (x86)\Java\jdk1.8.0_181\jre\lib\rt.jar]	
    [Loaded java.lang.reflect.Type from C:\Program Files (x86)\Java\jdk1.8.0_181\jre\lib\rt.jar]	
    [Loaded java.lang.Class from C:\Program Files (x86)\Java\jdk1.8.0_181\jre\lib\rt.jar]	
    。。。。。。。

**堆栈参数**

堆最大值： -Xmx20m

堆的最小值： -Xms5m

获取系统堆内存信息

System.out.println("堆最大空间：" + Runtime.getRuntime().maxMemory() / 1024 / 1024 + "M");	
    System.out.println("空闲空间：" + Runtime.getRuntime().freeMemory() / 1024 / 1024 + "M");	
    System.out.println("可用空间：" + Runtime.getRuntime().totalMemory() / 1024 / 1024 + "M");

新生代的内存： -Xmn10m

eden区和两个s区的和，正常情况下是eden:s0:s1=8:1:1

新生代占老年的的比值：-XX:NewRatio=6

新生代与老年代的比率为1:6，正常情况下是新生代:老年代=3:8

两个s区与eden的比值：-XX:SurvivorRatio=6

一个s区与eden的比率为1:6

发生堆溢出时异常文件路径：

\-XX:HeapDumpPath=d:\\appLog\\a.dump

发生堆溢出时候执行的脚本：

\-XX:OnOutOfMemoryError=d:\\a.sh

栈的大小-Xss10m

永久区的初始大小：-XX:PermSize5m

永久区的最大大小：-XX:MaxPermSize5m

元数据区大小：-XX:MaxMetaspaceSize=5m

点击下方“阅读原文”查看所有参数的示例使用代码！！！

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