Specify the GC as the CMS when jdk version less 9.

[aloneboat]

What is the purpose of the change

When Jdk version less than 9 , for example 8, the GC default is Parallel GC，the application threads will be pause for long time (as I understand it) ,that is not we want。
I find this change Support JDK 11，recovered some code

Brief changelog

Specify the GC as the CMS when jdk version less that 9.

[CLAassistant]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

Merging #10343 (a02dc6d) into develop (bbf1bd8) will increase coverage by 0.01%.
The diff coverage is n/a.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #10343      +/-   ##
=============================================
+ Coverage      54.31%   54.32%   +0.01%     
- Complexity      5435     5438       +3     
=============================================
  Files            879      879              
  Lines          27832    27832              
  Branches        3083     3083              
=============================================
+ Hits           15117    15121       +4     
+ Misses         11391    11386       -5     
- Partials        1324     1325       +1     

see 3 files with indirect coverage changes

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[iJIAJIA]

看了下gc配置, 有个疑惑点想讨论下, 这里为什么去除 -XX:-UseParNewGC. 我这边8c20g的3节点集群,跟默认使用UseParNewGC进行了3000的并发心跳压测对比, 吞吐量有10k左右的差距. 同时gc的频率也有差距.
启动时jvm也给了警告. 不推荐 cms 跟DefNew 搭配使用.

[iJIAJIA]

对比下来, cms + ParNewGC的gc频次是远低于 cms + DefNew 的

[iJIAJIA]

@aloneboat

[aloneboat]

@iJIAJIA Sorry for the late reply. you should be right, I just restored the earlier code，the purpose is simply to use the CMS garbage collector when jdk version less than 9, I didn't look closely at whether it was a plus or a minus before "ParNewGC",actually I agree with you.