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:
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:
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