使用DirectByteBuffer分配 Off-Heap 内存: importjava.nio.ByteBuffer;publicclassOffHeapMemoryExample{publicstaticvoidmain(String[] args){// 分配 10 MB 的堆外内存ByteBufferbuffer=ByteBuffer.allocateDirect(10*1024*1024);// 向堆外内存中写数据for(inti=0; i < buffer.capacity(); i++) { buffer.put((...
测试用例3:设置JVM参数-Xmx256m -XX:MaxDirectMemorySize=100M,运行异常,分配的直接内存128M超过限定的100M。 Exception in thread "main" java.lang.OutOfMemoryError: Direct buffer memory at java.nio.Bits.reserveMemory(Bits.java:658) at java.nio.DirectByteBuffer.<init>(DirectByteBuffer.java:123) at...
2. 堆外内存(off-heap memory) 2.1 堆外内存的产生 为了解决堆内内存过大带来的长时间的GC停顿的问题,以及操作系统对堆内内存不可知的问题,java虚拟机开辟出了堆外内存(off-heap memory)。堆外内存意味着把一些对象的实例分配在Java虚拟机堆内内存以外的内存区域,这些内存直接受操作系统(而不是虚拟机)管理。这...
# 正常运行时dumpjmap -dump:format=b,file=/tmp/heap.bin pid jmap -dump:live,format=b,file=/tmp/heap.bin pid# OOM 时自动dump-XX:+HeapDumpOnOutOfMemoryError# FullGC 前dump-XX:+HeapDumpBeforeFullGC# FullGC 后dump-XX:+HeapDumpAfterFullGC 可达性(Reachability),JVM 的垃圾收集器通过可达性分...
写道 Off heap memory provides; Scalability to large memory sizes e.g. over 1 TB and larger than main memory. Notional impact on GC pause times.
一、使用ByteBuffer.allocateDirect分配的off heap内存大小 本机进程 在Jvisualvm中安装 Mbeans插件。然后查看java.nio/BufferPool/direct 进程内使用代码获取 MBeanServermbs=ManagementFactory. getPlatformMBeanServer() ;ObjectNameobjectName=newObjectName("java.nio:type=BufferPool,name=direct") ;MBeanInfoinfo=mb...
如果排除DirectByteBuffer,那就是应用程序直接用Unsafe类的allocateMemory分配的内存,例如Spark的off heap memory[1]。此时可排查代码所有Unsafe.allocateMemory的地方。 Java调用C++组件 例如RocksDB采用C++实现,并通过JNI提供给Java调用的接口,如果Java通过JNI创建了新的RocksDB实例,RocksDB会启动若干后台线程申请、释放内存...
Version of Slice before 2.0 support off-heap memory and can be backed by any Java primitive array type. These features were rarely used, and were removed in version 2.0 to simplify the codebase. If you need these versions, they are available in therelease-0.xbranch. ...
Almost every Java application uses some native (off-heap) memory. For most apps, this amount is relatively modest. However, in some situations, you may discover that your app's RSS (total memory used by the process) is much bigger than its heap size. If this is not something that you ...
With a Java heap size constrained to be very small (say, 16 MB) you can create an in-memory, off-heap data store that holds gigabytes of data—or even more. Here’s the story: I developed a basic storage solution for a project using Java’sMappedByteBufferclass coupled with aRandomAcce...