Why do you need to use the JDK 11 instead of 8?


Gonchik in touch. 

As we know Garbage-First is quite a popular garbage collector nowadays. At least more and more articles, product documentation mention G1GC. 

Today, I’d like to share a story about leaked Jira Service Desk DC (3 nodes) with more than 20 apps from the marketplace, quite a lot of groovy scripts (405 files), 6 in-house apps. Also, it's continue of previous article.

One of the instances every night do import files into the “Insight” app, those asset management includes too many assets around 1 mln, as it’s daily import history of objects can grow as well.

Let’s focus only on importing procedure, we had 1 dedicated instance with 32GB heap for jdk8u282-b08 and G1GC. During import find out the next behaviour:

# cat atlassian-jira-gc.0.current| grep -i "full"

2021-03-30T21:13:19.462+0300: 934.828: [Full GC (Allocation Failure)  31309M->23165M(32768M), 58.7721842 secs]
2021-03-30T21:14:31.997+0300: 1007.363: [Full GC (Allocation Failure)  28965M->23085M(32768M), 53.9423610 secs]
2021-03-30T21:15:58.527+0300: 1093.893: [Full GC (Allocation Failure)  29277M->23233M(32768M), 55.0332227 secs]
2021-03-30T21:17:18.147+0300: 1173.513: [Full GC (Allocation Failure)  29249M->23469M(32768M), 56.4150710 secs]
2021-03-30T21:18:28.114+0300: 1243.480: [Full GC (Allocation Failure)  29253M->23540M(32768M), 56.5262454 secs]


After just updating the  jdk to jdk-11.0.10+9, we can find improvement only for the full GC activity. 

# cat atlassian-jira-gc.1.log.0 | grep -i "full "

[2021-04-07T07:58:29.710+0300] GC(3745) Using 11 workers of 11 for full compaction
[2021-04-07T07:58:29.710+0300] GC(3745) Pause Full (G1 Evacuation Pause)
[2021-04-07T07:58:39.163+0300] GC(3745) Pause Full (G1 Evacuation Pause) 32768M->24074M(32768M) 9452.818ms
[2021-04-07T08:54:55.518+0300] GC(6005) Using 11 workers of 11 for full compaction
[2021-04-07T08:54:55.518+0300] GC(6005) Pause Full (G1 Evacuation Pause)
[2021-04-07T08:55:05.032+0300] GC(6005) Pause Full (G1 Evacuation Pause) 32734M->25724M(32768M) 9513.629ms
[2021-04-07T08:55:32.812+0300] GC(6070) Using 11 workers of 11 for full compaction
[2021-04-07T08:55:32.812+0300] GC(6070) Pause Full (G1 Evacuation Pause)
[2021-04-07T08:55:41.549+0300] GC(6070) Pause Full (G1 Evacuation Pause) 32714M->25595M(32768M) 8736.933ms

So especially did not change the parameters in that article, to make GC improvements with next parameters: InitiatingHeapOccupancyPercent, UseCompressedClassPointers, UseCompressedOops, MaxGCPauseMillis, OmitStackTraceInFastThrow, UseStringDeduplication.

What’s happened, why does Full GC on JDK8 work so slow? If you look on htop, you can see only 1 CPU is busy. 


After looking at the picture, the next JEP-307 (ParallelGC for FullGC), https://openjdk.java.net/jeps/307 is a motivating upgrade to Java 11. 

And, please, don’t forget to checkout compatibility on the Supported platforms page.

In conclusion, if you’re using G1GC in JRE 8, you can meet with small problems once Full GC will be called and your system can be freezed for a long time instead of JRE 11.


Hope it helps to make a decision.




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