我在Java 8上运行了一个服务器应用程序:
:-XX:GCLogFileSize=2097152 -XX:InitialBootClassLoaderMetaspaceSize=33554432 -XX:InitialHeapSize=1610612736 -XX:MaxHeapSize=1610612736 -XX:MaxMetaspaceSize=1073741824 -XX:MetaspaceSize=536870912 -XX:NumberOfGCLogFiles=5 -XX:+PrintGC -XX:+PrintGCApplicationConcurrentTime -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseGCLogFileRotation -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC
Metaspace的起始值为512m,最大值为1GB。
在GC日志中,我看到的Metaspace值与上述标志值不同。我的日志样本如下:
{Heap before GC invocations=1 (full 0):
PSYoungGen total 458752K, used 393216K [0x00000000e0000000, 0x0000000100000000, 0x0000000100000000)
eden space 393216K, 100% used [0x00000000e0000000,0x00000000f8000000,0x00000000f8000000)
from space 65536K, 0% used [0x00000000fc000000,0x00000000fc000000,0x0000000100000000)
to space 65536K, 0% used [0x00000000f8000000,0x00000000f8000000,0x00000000fc000000)
ParOldGen total 1048576K, used 0K [0x00000000a0000000, 0x00000000e0000000, 0x00000000e0000000)
object space 1048576K, 0% used [0x00000000a0000000,0x00000000a00003a0,0x00000000e0000000)
Metaspace used 26975K, capacity 54120K, committed 54400K, reserved 1114112K
class space used 3346K, capacity 4426K, committed 4480K, reserved 1048576K
2016-12-21T16:41:10.569+0300: 1.423: [GC (GCLocker Initiated GC) [PSYoungGen: 393216K->29645K(458752K)] 393216K->29734K(1507328K), 0.0241803 secs] [Times: user=0.11 sys=0.00, real=0.02 secs]
Heap after GC invocations=1 (full 0):
PSYoungGen total 458752K, used 29645K [0x00000000e0000000, 0x0000000100000000, 0x0000000100000000)
eden space 393216K, 0% used [0x00000000e0000000,0x00000000e0000000,0x00000000f8000000)
from space 65536K, 45% used [0x00000000f8000000,0x00000000f9cf3460,0x00000000fc000000)
to space 65536K, 0% used [0x00000000fc000000,0x00000000fc000000,0x0000000100000000)
ParOldGen total 1048576K, used 88K [0x00000000a0000000, 0x00000000e0000000, 0x00000000e0000000)
object space 1048576K, 0% used [0x00000000a0000000,0x00000000a00163b0,0x00000000e0000000)
Metaspace used 26975K, capacity 54120K, committed 54400K, reserved 1114112K
class space used 3346K, capacity 4426K, committed 4480K, reserved 1048576K
}
所以我的问题是:为什么我不在GC日志中看到Metaspace的512m和1GB值?日志值是否与标志直接相关?
,如"高级垃圾收集选项"中所述:
- -XX:METASPACESIZE = size
设置了分配的类元数据空间的大小,该大小将在第一次超过垃圾时触发垃圾收集。根据所使用的元数据的数量,增加或减少了垃圾收集的阈值。默认大小取决于平台。
换句话说,它没有指定初始大小,而是第一次GC阈值,因此它与您观察到的行为不具有完整的GC,而实际的Metaspace大小小于指定的大小。
一旦第一次超过阈值,JVM可能会根据实际用法选择新的阈值。