Difference between pause average time and full gc average time

Hi Rizwan,

1) Difference between pause average time and full GC average time -

Pause average time - It is the average time taken by the stop the world GC event that is total time taken by all stop the world events / number of stop the world events. Say you have total 3 stop the world events and it took total 6 seconds then the average time will be 2 seconds.

Full GC average time - Average time is taken by the full GC events that are the total time taken by all full GC events / number of full GC events

2) Allocation Failure - It is not an error but is a totally normal case in JVM. This is a typical GC event which causes the Java Garbage Collection process to get triggered. "Allocation Failure" means that no more space left in Eden to allocate object. So, it is normal cause of young GC. Garbage Collection removes dead objects, compact reclaimed memory and thus helps in freeing up memory for new object allocations.

3) GCLocker initiated GC - GC started after all threads leave the JNI critical region. For more information on JNI, refer to the Java Native Interface documentation website. GC is blocked when any thread is in the JNI critical region and can start only when all of them outside of it.

Hello Rizwan!

 Greetings.

1. What is the difference between Average GC Pause time and Average Full GC Pause time?

 It's wide misnomer in the industry that minor GC don't pause the JVM. Minor JVM also pause the JVM, but they pause for comparatively smaller duration than Full GC (in most cases).

 Also in one single major GC event there are also multiple phases (like clean, mark, remark, concurrent-mark,....) - not all of the phases pause the JVM. Only few of those phases pause the the JVM.

 When we report  Average GC Pause time - we account only the minor GC and the phases of the major GC that causes the stop-the-world event.

 When we report Average Full GC time - we account entire full GC's time.

 For all practical purpose for your study you can the time reported in the KPI section of the report: