java gc日志内容分析-YoungGC-FullGC

環境版本，Java1.8，GC日志參數

-XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintGCApplicationStoppedTime 
-XX:+PrintGCApplicationConcurrentTime -XX:+PrintHeapAtGC
           

YoungGC找到一條輸出的日志：

2335.667: Total time for which application threads were stopped: 0.0042227 seconds, Stopping threads took: 0.0000467 seconds
2335.879: Application time: 0.2122459 seconds
{Heap before GC invocations=741 (full 3):
 def new generation   total 176960K, used 157479K [0x00000000e8000000, 0x00000000f4000000, 0x00000000f4000000)
  eden space 157312K, 100% used [0x00000000e8000000, 0x00000000f19a0000, 0x00000000f19a0000)
  from space 19648K,   0% used [0x00000000f19a0000, 0x00000000f19c9fe8, 0x00000000f2cd0000)
  to   space 19648K,   0% used [0x00000000f2cd0000, 0x00000000f2cd0000, 0x00000000f4000000)
 tenured generation   total 196608K, used 47047K [0x00000000f4000000, 0x0000000100000000, 0x0000000100000000)
   the space 196608K,  23% used [0x00000000f4000000, 0x00000000f6df1ec8, 0x00000000f6df2000, 0x0000000100000000)
 Metaspace       used 67465K, capacity 70294K, committed 70552K, reserved 1110016K
  class space    used 8778K, capacity 9290K, committed 9368K, reserved 1048576K
           

日志分析：

1）2335.667: Total time for which application threads were stopped: 0.0042227 seconds, Stopping threads took: 0.0000467 seconds

2335.667:  這裡表示JVM執行了多久時間，機關是秒。在gc的時候，顯示程式暫停的時間

2）2335.879: Application time: 0.2122459 seconds

表示在發生GC的時候，程式執行的時間，由于是tomcat的日志，這個表示請求響應時間為0.2122459 seconds

3）新生代區gc日志

 def new generation   total 176960K, used 157479K   新生去總共176960K，已使用157479K   

  eden space 157312K, 100% used  //伊甸區

  from space 19648K,   0% used   //From Survivor，占新生代10%

  to   space 19648K,   0% used     //To Surivor，占新生代10%

 Survivor的目的，減少進入老年代的對象，進而減少fullGC的次數

4）老年代占用

tenured generation total 196608K, used 47047K

5）永久區占用

 Metaspace       used 67465K, capacity 70294K, committed 70552K, reserved 1110016K

  class space    used 8778K, capacity 9290K, committed 9368K, reserved 1048576K