Make ExplicitGCInvokesConcurrent default for Jira

Problem Definition

If you use the Garbage-First (G1) garbage collector, we recommend configuring your JVM parameters to avoid the risk of explicit STW (stop the world) GC, which causes Jira to become unavailable while the garbage collection cycle runs.

See Health Check: Explicit Garbage Collection for more details

Suggested Solution

Add '-XX:+ExplicitGCInvokesConcurrent' by default to Jira.

• It will be used by G1GC and CMS.
  • https://bugs.openjdk.java.net/browse/JDK-8160392
• It will be ignored by ParallelGC since there is no Concurrent phase for OldGen.

Context:

Other causes than Allocation Failure for a Full GC typically indicate that either the application or some external tool causes a full heap collection. If the cause is System.gc(), and there is no way to modify the application sources, the effect of Full GCs can be mitigated by using -XX:+ExplicitGCInvokesConcurrent

from https://docs.oracle.com/javase/9/gctuning/garbage-first-garbage-collector-tuning.htm#JSGCT-GUID-2428DA90-B93D-48E6-B336-A849ADF1C552

Workaround

None