JVM垃圾回收篇-案例分析
JVM常用参数
| 含义 | 参数 |
|---|---|
| 堆初始大小 | -Xms |
| 堆最大大小 | -Xmx 或 -XX:MaxHeapSize=size |
| 新生代大小 | -Xmn 或 (-XX:NewSize=size + -XX:MaxNewSize=size ) |
| 幸存区比例（动态） | -XX:InitialSurvivorRatio=ratio 和 -XX:+UseAdaptiveSizePolicy |
| 幸存区比例 | -XX:SurvivorRatio=ratio |
| 晋升阈值 | -XX:MaxTenuringThreshold=threshold |
| 晋升详情 | -XX:+PrintTenuringDistribution |
| GC详情 | -XX:+PrintGCDetails -verbose:gc |
| FullGC 前 MinorGC | -XX:+ScavengeBeforeFullGC |
初始化
import java.util.ArrayList;
/**
* @apiNote -Xms20M -Xmx20M -Xmn10M -XX:+UseSerialGC -XX:+PrintGCDetails -verbose:gc
*/
public class Demo4 {
private static final int _512KB = 512 * 1024;
private static final int _1MB = 1024 * 1024;
private static final int _6MB = 6 * 1024 * 1024;
private static final int _7MB = 7 * 1024 * 1024;
private static final int _8MB = 8 * 1024 * 1024;
public static void main(String[] args) {
}
}
运行结果
Heap
def new generation total 9216K, used 2033K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
eden space 8192K, 24% used [0x00000000fec00000, 0x00000000fedfc658, 0x00000000ff400000)
from space 1024K, 0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
to space 1024K, 0% used [0x00000000ff500000, 0x00000000ff500000, 0x00000000ff600000)
tenured generation total 10240K, used 0K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
the space 10240K, 0% used [0x00000000ff600000, 0x00000000ff600000, 0x00000000ff600200, 0x0000000100000000)
Metaspace used 3245K, capacity 4496K, committed 4864K, reserved 1056768K
class space used 343K, capacity 388K, committed 512K, reserved 1048576K
创建一个7MB的数组
public static void main(String[] args) {
ArrayList<byte[]> list = new ArrayList<>();
list.add(new byte[_7MB]);
}
运行结果
[GC (Allocation Failure) [DefNew: 1869K->689K(9216K), 0.0009946 secs] 1869K->689K(19456K), 0.0010279 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
Heap
def new generation total 9216K, used 8267K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
eden space 8192K, 92% used [0x00000000fec00000, 0x00000000ff366830, 0x00000000ff400000)
from space 1024K, 67% used [0x00000000ff500000, 0x00000000ff5ac488, 0x00000000ff600000)
to space 1024K, 0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
tenured generation total 10240K, used 0K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
the space 10240K, 0% used [0x00000000ff600000, 0x00000000ff600000, 0x00000000ff600200, 0x0000000100000000)
Metaspace used 3368K, capacity 4496K, committed 4864K, reserved 1056768K
class space used 357K, capacity 388K, committed 512K, reserved 1048576K
- 触发了一次
minor gc
[GC (Allocation Failure) [DefNew[发生在新生代]: 1880K->692K(9216K)[gc之前占用内存空间->gc之后占用内存空间(总的新生代内存空间大小)], 0.0018135 secs[回收时间]
1880K->692K(19456K)[堆内存gc前占用大小->堆内存gc后占用大小(堆内存总大小)], 0.0028038 secs[堆内存gc消耗时间] [Times: user=0.00 sys=0.00, real=0.00 secs]
再加入512KB数组
public static void main(String[] args) {
ArrayList<byte[]> list = new ArrayList<>();
list.add(new byte[_7MB]);
list.add(new byte[_512KB]);
}
运行结果
[GC (Allocation Failure) [DefNew: 1869K->689K(9216K), 0.0020982 secs] 1869K->689K(19456K), 0.0021583 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
Heap
def new generation total 9216K, used 8779K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
eden space 8192K, 98% used [0x00000000fec00000, 0x00000000ff3e6840, 0x00000000ff400000)
from space 1024K, 67% used [0x00000000ff500000, 0x00000000ff5ac588, 0x00000000ff600000)
to space 1024K, 0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
tenured generation total 10240K, used 0K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
the space 10240K, 0% used [0x00000000ff600000, 0x00000000ff600000, 0x00000000ff600200, 0x0000000100000000)
Metaspace used 3424K, capacity 4496K, committed 4864K, reserved 1056768K
class space used 365K, capacity 388K, committed 512K, reserved 1048576K
- 还是只触发一次
gc
再加入512KB数组
public static void main(String[] args) {
ArrayList<byte[]> list = new ArrayList<>();
list.add(new byte[_7MB]);
list.add(new byte[_512KB]);
list.add(new byte[_512KB]);
}
运行结果
[GC (Allocation Failure) [DefNew: 1869K->687K(9216K), 0.0015233 secs] 1869K->687K(19456K), 0.0015748 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
[GC (Allocation Failure) [DefNew: 8695K->524K(9216K), 0.0032424 secs] 8695K->8374K(19456K), 0.0032650 secs] [Times: user=0.01 sys=0.00, real=0.00 secs]
Heap
def new generation total 9216K, used 1362K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
eden space 8192K, 10% used [0x00000000fec00000, 0x00000000fecd1840, 0x00000000ff400000)
from space 1024K, 51% used [0x00000000ff400000, 0x00000000ff483070, 0x00000000ff500000)
to space 1024K, 0% used [0x00000000ff500000, 0x00000000ff500000, 0x00000000ff600000)
tenured generation total 10240K, used 7850K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
the space 10240K, 76% used [0x00000000ff600000, 0x00000000ffdaab68, 0x00000000ffdaac00, 0x0000000100000000)
Metaspace used 3420K, capacity 4496K, committed 4864K, reserved 1056768K
class space used 364K, capacity 388K, committed 512K, reserved 1048576K
-
可以看到触发了两次
minor gc -
由于新生代内存不足，一些对象进入了老年代
大对象的直接晋升
public static void main(String[] args) {
ArrayList<byte[]> list = new ArrayList<>();
list.add(new byte[_8MB]);
}
输出结果
Heap
def new generation total 9216K, used 2208K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
eden space 8192K, 26% used [0x00000000fec00000, 0x00000000fee28188, 0x00000000ff400000)
from space 1024K, 0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
to space 1024K, 0% used [0x00000000ff500000, 0x00000000ff500000, 0x00000000ff600000)
tenured generation total 10240K, used 8192K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
the space 10240K, 80% used [0x00000000ff600000, 0x00000000ffe00010, 0x00000000ffe00200, 0x0000000100000000)
Metaspace used 3421K, capacity 4496K, committed 4864K, reserved 1056768K
class space used 364K, capacity 388K, committed 512K, reserved 1048576K
- 当新生代无法容纳下对象时，jvm不会触发gc[因为gc后空间仍然无法容纳下该对象]，而是将对象直接晋升到老年代
OOM
public static void main(String[] args) {
ArrayList<byte[]> list = new ArrayList<>();
list.add(new byte[_8MB]);
list.add(new byte[_8MB]);
}
输出结果文章来源：https://www.toymoban.com/news/detail-636435.html
[GC (Allocation Failure) [DefNew: 2208K->705K(9216K), 0.0014397 secs][Tenured: 8192K->8896K(10240K), 0.0036360 secs] 10400K->8896K(19456K), [Metaspace: 3422K->3422K(1056768K)], 0.0051423 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
[Full GC (Allocation Failure) [Tenured: 8896K->8870K(10240K), 0.0016408 secs] 8896K->8870K(19456K), [Metaspace: 3422K->3422K(1056768K)], 0.0016661 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
Heap
def new generation total 9216K, used 410K [0x00000000fec00000, 0x00000000ff600000, 0x00000000ff600000)
eden space 8192K, 5% used [0x00000000fec00000, 0x00000000fec66800, 0x00000000ff400000)
from space 1024K, 0% used [0x00000000ff500000, 0x00000000ff500000, 0x00000000ff600000)
to space 1024K, 0% used [0x00000000ff400000, 0x00000000ff400000, 0x00000000ff500000)
tenured generation total 10240K, used 8870K [0x00000000ff600000, 0x0000000100000000, 0x0000000100000000)
the space 10240K, 86% used [0x00000000ff600000, 0x00000000ffea9998, 0x00000000ffea9a00, 0x0000000100000000)
Metaspace used 3473K, capacity 4496K, committed 4864K, reserved 1056768K
class space used 371K, capacity 388K, committed 512K, reserved 1048576K
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at com.vmware.chat2.Demo4.main(Demo4.java:19)
- 先进行一次
minor gc发现内存仍然不足后触发了一次full gc,空间依然不足引发了oom
🔖线程内的oom不会导致整个进程结束文章来源地址https://www.toymoban.com/news/detail-636435.html
到了这里，关于JVM垃圾回收篇-案例分析的文章就介绍完了。如果您还想了解更多内容，请在右上角搜索TOY模板网以前的文章或继续浏览下面的相关文章，希望大家以后多多支持TOY模板网！
