java - 升级失败时gc log的含义

Question

发生promotion failure时出现以下gc日志是什么意思？

2019-07-24T23:58:32.113+0800: 1731400.358: [ParNew 
(0: promotion failure size = 3)
(1: promotion failure size = 2)  
(2: promotion failure size = 2)
(3: promotion failure size = 2)  
(4: promotion failure size = 3)
(6: promotion failure size = 2)  
(7: promotion failure size = 65538)
(8: promotion failure size = 2)  
(9: promotion failure size = 9)
(0: promotion failure size = 3)  
(1: promotion failure size = 2)
(2: promotion failure size = 2)  
(3: promotion failure size = 2)
(4: promotion failure size = 3)
(6: promotion failure size = 2)
(7: promotion failure size = 65538)
(8: promotion failure size = 2)
(9: promotion failure size = 9)
(0: promotion failure size = 3)
(1: promotion failure size = 2)
(2: promotion failure size = 2)
(3: promotion failure size = 2)
(4: promotion failure size = 3)
(6: promotion failure size = 2)
(7: promotion failure size = 65538)
(8: promotion failure size = 2)
(9: promotion failure size = 9)
(0: promotion failure size = 3)
(1: promotion failure size = 2)
(2: promotion failure size = 2)
(3: promotion failure size = 2)
(4: promotion failure size = 3)
(6: promotion failure size = 2)
(7: promotion failure size = 65538)
(8: promotion failure size = 2)
(9: promotion failure size = 9)
(0: promotion failure size = 3)
(1: promotion failure size = 2)
(2: promotion failure size = 2)
(3: promotion failure size = 2)
(4: promotion failure size = 3)
(6: promotion failure size = 2)
(7: promotion failure size = 65538)
(8: promotion failure size = 2)
(9: promotion failure size = 9)
(0: promotion failure size = 3)
(1: promotion failure size = 2)
(2: promotion failure size = 2)
(3: promotion failure size = 2)
(4: promotion failure size = 3)
(6: promotion failure size = 2)
(7: promotion failure size = 65538)
(8: promotion failure size = 2)
(9: promotion failure size = 9)
(0: promotion failure size = 3) 

我使用parNew + CMS。

JDK 1.8_102

Answer 1

提升失败是指垃圾收集在旧代中找不到足够的(连续)空间来将对象从新一代提升到其中时发生。

简单的解决方案是增加老年代堆大小。 This doc对你有帮助。

另一种解决方案，使用带 -XX:+UseG1GC 标志的 GC1 算法。因为在老年代碎片方面，G1 GC比CMS更成功。 Oracle doc说:

The G1 GC reduces heap fragmentation by incremental parallel copying of live objects from one or more sets of regions (called Collection Set (CSet)) into different new region(s) to achieve compaction. The goal is to reclaim as much heap space as possible, starting with those regions that contain the most reclaimable space, while attempting to not exceed the pause time goal (garbage first).