All GC in HotSpot uses generation, and a critical part in understand performance is often to understand what objects survive and are promoted to the old space.

To keep overhead low events are only created for objects that are directly promoted or if a new PLAB is required, in a similar fashion as the allocation event. This supported GCs are CMS, Parallel an G1. The serial collector and promotion of objects in CMS will not be included as these GC (or parts of) do not use PLABs and tracing all promoted objects would be too costly.

The event will capture the object type, object age, if it was copied to a PLAB (size of PLAB) or if it was directly to the heap, and if the object was aged in survivor area or promoted to the tenured generation. The event will also capture the thread promoting the object and hence help detect if the GC threads are unbalanced. There will not be any stacktrace collected as the trace would not give any further information about the allocation site or usage of the object being aged/promoted.