GC日志分析

# GC日志参数分析

public class _01PrintGCDetails {
    public static void main(String[] args) {
        ArrayList<byte[]> list = new ArrayList<>();
        for (int i = 0; i < 500; i++) {
            byte[] arr = new byte[1024 * 1024];
            list.add(arr);
        }
    }
}

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[GC (Allocation Failure) [DefNew: 3843K->512K(4928K), 0.0034569 secs] 3843K->2649K(15872K), 0.0043457 secs] [Times: user=0.02 sys=0.00, real=0.00 secs] 
[GC (Allocation Failure) [DefNew: 4738K->0K(4928K), 0.0038790 secs] 6875K->6745K(15872K), 0.0039024 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 
[GC (Allocation Failure) [DefNew: 4205K->0K(4928K), 0.0024967 secs] 10950K->10841K(15872K), 0.0025230 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 
[GC (Allocation Failure) [DefNew: 4220K->1K(4928K), 0.0038292 secs][Tenured: 14937K->14938K(15056K), 0.0015664 secs] 15061K->14938K(19984K), [Metaspace: 2252K->2252K(4480K)], 0.0055458 secs] [Times: user=0.02 sys=0.00, real=0.01 secs] 
[GC (Allocation Failure) [DefNew: 9435K->1027K(11264K), 0.0091230 secs] 24374K->24158K(36164K), 0.0091612 secs] [Times: user=0.00 sys=0.00, real=0.01 secs] 
[GC (Allocation Failure) [DefNew: 10447K->1024K(11264K), 0.0075598 secs][Tenured: 32350K->32350K(33124K), 0.0017955 secs] 33578K->33374K(44388K), [Metaspace: 2279K->2279K(4480K)], 0.0095590 secs] [Times: user=0.00 sys=0.01, real=0.01 secs] 
[GC (Allocation Failure) [DefNew: 21373K->2072K(24320K), 0.0132403 secs] 53724K->52855K(78240K), 0.0132947 secs] [Times: user=0.00 sys=0.02, real=0.01 secs] 
[GC (Allocation Failure) [DefNew: 22954K->2048K(24320K), 0.0126333 secs][Tenured: 71288K->71288K(71396K), 0.0020584 secs] 73738K->73336K(95716K), [Metaspace: 2283K->2283K(4480K)], 0.0150118 secs] [Times: user=0.02 sys=0.00, real=0.01 secs] 
[GC (Allocation Failure) [DefNew: 46984K->5120K(53568K), 0.0272463 secs] 118272K->117369K(172384K), 0.0273079 secs] [Times: user=0.02 sys=0.01, real=0.03 secs] 
[GC (Allocation Failure) [DefNew: 52101K->5120K(53568K), 0.0294453 secs][Tenured: 158330K->158302K(158908K), 0.0266126 secs] 164350K->163422K(212476K), [Metaspace: 2283K->2283K(4480K)], 0.0563373 secs] [Times: user=0.05 sys=0.02, real=0.06 secs] 
[GC (Allocation Failure) [DefNew: 69947K->69947K(78656K), 0.0000182 secs][Tenured: 158302K->174687K(174784K), 0.0243151 secs] 228249K->227936K(253440K), [Metaspace: 2283K->2283K(4480K)], 0.0243971 secs] [Times: user=0.03 sys=0.00, real=0.03 secs] 
[Full GC (Allocation Failure) [Tenured: 174687K->174687K(174784K), 0.0027962 secs] 252803K->252513K(253440K), [Metaspace: 2283K->2283K(4480K)], 0.0028338 secs] [Times: user=0.02 sys=0.00, real=0.00 secs] 
[Full GC (Allocation Failure) [Tenured: 174687K->174670K(174784K), 0.0309642 secs] 252513K->252496K(253440K), [Metaspace: 2283K->2283K(4480K)], 0.0310148 secs] [Times: user=0.03 sys=0.00, real=0.03 secs] 
Heap
 def new generation   total 78656K, used 78148K [0x05600000, 0x0ab50000, 0x0ab50000)
  eden space 69952K, 100% used [0x05600000, 0x09a50000, 0x09a50000)
  from space 8704K,  94% used [0x09a50000, 0x0a251168, 0x0a2d0000)
  to   space 8704K,   0% used [0x0a2d0000, 0x0a2d0000, 0x0ab50000)
 tenured generation   total 174784K, used 174670K [0x0ab50000, 0x15600000, 0x15600000)
   the space 174784K,  99% used [0x0ab50000, 0x155e3850, 0x155e3a00, 0x15600000)
 Metaspace       used 2303K, capacity 2344K, committed 2368K, reserved 4480K
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
    at gc.logs._01PrintGCDetails.main(_01PrintGCDetails.java:14)

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【参数解析】

GC、Full GC： GC的类型
- GC只在新生代上进行
- Full GC包括永久代(元空间)，新生代，老年代
Allocation Failure： GC发生的原因，即内存分配失败
21373K->2072K：堆在GC前的使用大小和GC后的使用大小
78656K：堆空间的总大小
0.0273079 secs： GC耗时
PSYoungGen：表示当前使用了Parallel Scavenge并行垃圾收集器进行新生代回收
ParOldGen：表示当前使用了Parallel Old并行垃圾收集器进行老年代回收
Metaspace：元数据区GC前后大小的变化，JDK1.8中引入了元数据区以替代永久代
Times： user：指的是垃圾收集器花费的所有CPU时间，sys：花费在等待系统调用或系统事件的时间，real：GC从开始到结束的时间，包括其他进程占用时间片的实际时间
Heap：整个堆内存的详细使用以及回收情况