JVM family -- heap analysis

One .MAT brief introduction

MAT It's an analysis tool , Installation is omitted .

Two . To configure

appear oom export dump file , Analysis report

3、 ... and . Reactor analysis

1.OOM( out of memory ) reason ：

StackOverFlow Stack ,Stack Area belonging to stack , Private to each thread

HeapOutOfMemory Pile up

ConstantOutOfMemory Constant pool

DirectMemoryOutOfmemory Local memory

2. Heap overflow

public static void main(String args[]){

ArrayList<byte[]> list=new ArrayList<byte[]>();

for(int i=0;i<1024;i++){

list.add(new byte[1024*1024]);

}

} 

Take up a lot of heap space , Direct spillover , resolvent ： Increase heap space , Free memory in time

Generate a large number of classes

public static void main(String[] args) {

for(int i=0;i<100000;i++){

CglibBean bean = new CglibBean("geym.jvm.ch3.perm.bean"+i,new HashMap());

}

}

Caused by: java.lang.OutOfMemoryError: PermGen space

[Full GC[Tenured: 2523K->2523K(10944K), 0.0125610 secs] 2523K->2523K(15936K), 

[Perm : 4095K->4095K(4096K)], 0.0125868 secs] [Times: user=0.02 sys=0.00, real=0.01 secs] 

Heap

def new generation total 4992K, used 89K [0x28280000, 0x287e0000, 0x2d7d0000)

eden space 4480K, 2% used [0x28280000, 0x282966d0, 0x286e0000)

from space 512K, 0% used [0x286e0000, 0x286e0000, 0x28760000)

to space 512K, 0% used [0x28760000, 0x28760000, 0x287e0000)

tenured generation total 10944K, used 2523K [0x2d7d0000, 0x2e280000, 0x38280000)

the space 10944K, 23% used [0x2d7d0000, 0x2da46cf0, 0x2da46e00, 0x2e280000)

compacting perm gen total 4096K, used 4095K [0x38280000, 0x38680000, 0x38680000)

the space 4096K, 99% used [0x38280000, 0x3867fff0, 0x38680000, 0x38680000)

ro space 10240K, 44% used [0x38680000, 0x38af73f0, 0x38af7400, 0x39080000)

rw space 12288K, 52% used [0x39080000, 0x396cdd28, 0x396cde00, 0x39c80000)

resolvent ：

increase Perm District

allow Class Recycling  

3.Java Stack overflow

When creating a thread , You need to allocate stack space for threads , This stack space is requested from the operating system , If the operating system cannot give enough space , Will throw OOM

resolvent ：

Reduce heap memory

Reduce the thread stack size

4. Direct memory overflow

Direct memory overflow

ByteBuffer.allocateDirect() Unable to get enough space from the operating system

resolvent ：

Reduce heap memory

Intentional trigger GC

Four . Dominate the tree

5、 ... and . Shallow pile  

1. The amount of memory occupied by an object structure

2. The object size is in accordance with 8 Byte alignment  

3. The shallow heap size has nothing to do with the content of the object , Only related to the structure of the object  

6、 ... and . Deep pile

1. An object is GC After recycling , The amount of memory that can actually be released

2. Accessible only through objects （ Directly or indirectly ） Sum of all objects in shallow heap （ Dominate the tree ）