JVM 的内存模型及jstat命令的使用

港控/mmm° 2023-10-07 08:12 1阅读 0赞

**目录**

--------------------

JVM的内存模型

jdk1.7的内存模型

jdk1.8的内存模型

为什么要废弃1.7中的永久代？

通过jstat命令查看堆内存使用情况

查看class加载统计

查看编译统计

垃圾回收统计

--------------------

## JVM的内存模型 ##

![20200115124239217.png][]

### jdk1.7的内存模型 ###

> new出来的对象，首先会存放在年轻代的Eden区；
> 
> 经过多次YGC后依然存活的对象会移进老年代；
> 
> new出来的如果是一个大对象的话会直接进入老年代。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly96aGFuZ3h1ZWxpYW5nLmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly96aGFuZ3h1ZWxpYW5nLmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70 1][]

### jdk1.8的内存模型 ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly96aGFuZ3h1ZWxpYW5nLmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70 2][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly96aGFuZ3h1ZWxpYW5nLmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70 3][]

> Metaspace元数据区占用的是服务器的内存空间，也就是本地内存空间，因为它不在虚拟机内部。这也是与1.7永久代的最大区别所在。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly96aGFuZ3h1ZWxpYW5nLmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70 4][]

### 为什么要废弃1.7中的永久代？ ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly96aGFuZ3h1ZWxpYW5nLmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70 5][]

### 通过jstat命令查看堆内存使用情况 ###

![20200115131520399.png][]

#### 查看class加载统计 ####

![20200115132649132.png][]

![20200115132802282.png][]

#### 查看编译统计 ####

![20200115133212123.png][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly96aGFuZ3h1ZWxpYW5nLmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70 6][]

#### 垃圾回收统计 ####

> jstat -gc 进程ID

![2020011516410672.png][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly96aGFuZ3h1ZWxpYW5nLmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70 7][]

> 每1000ms打印一次GC信息，一共打印10次：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly96aGFuZ3h1ZWxpYW5nLmJsb2cuY3Nkbi5uZXQ_size_16_color_FFFFFF_t_70 8][]

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