Fred,
Thanks for the clarification. You're totally right that the end of the
individual CMS pauses should not be seen as major GCs.
Tony
On 11/17/2011 9:27 AM, Frederic Parain wrote:
On 11/17/11 3:09 PM, Tony Printezis wrote:
Fred,
I haven't been following this thread closely, but I do have a question
(see below).
On 11/17/2011 8:43 AM, Frederic Parain wrote:
Hi Mandy,
It would have been nice to have notifications providing
detailed information about CMS different phases, but it
doesn't seem easy to do right now. I did the experiments
with CMS using JConsole, and the result is not really
satisfactory:
- several notifications are sent for each CMS cycle
but the notification lacks the information to identify
the CMS phase associated with the notification (worse
than that, they all claim they notify the "end of a major
GC cycle" which is certainly not true for CMS.
Are you referring to notifications at the end of a concurrent cycle
(i.e., at the end of sweeping)? Depends on how you look at it, but a
concurrent cycle is a major cycle given that it collects the entire
heap. In fact, IIRC, the a concurrent cycle should increase the full gc
count.
I'm not referring to the concurrent cycles, but to the different phases
of CMS. It seems that CMS is calling GCMemoryManager::gc_end() after
the initial marking, the final marking and the sweeping phase. The
gc count (_num_collections) is incremented only after the completion of
the sweeping phase. The actual notification code is confused
by the fact that CMS is executing GCMemoryManager::gc_end() several
times during a GC cycle. I made the assumption that calling gc_end()
means that the GC cycle is completed, but this assumption is wrong
with CMS, so the notification message is wrong in this case.
Fred
