Hello Vitaly,
On 8/24/2016 3:55 PM, Vitaly Davidovich wrote:
On Wed, Aug 24, 2016 at 6:29 PM, Poonam Bajaj Parhar
<poonam.ba...@oracle.com <mailto:poonam.ba...@oracle.com>> wrote:
Also, do you see entries like "/[G1Ergonomics (Mixed GCs) do not
start mixed GCs, reason:" /in the GC logs which mean that the
mixed GCs are not happening due to some reason. What is the reason
listed with these log entries?
Hi Poonam,
Yes, I do see a few those, but only very early in the process
lifetime, and nowhere near the Full GCs.
2016-08-24T10:33:04.733+0000: 8.460: [SoftReference, 0 refs, 0.0010108
secs]2016-08-24T10:33:04.734+0000: 8.461: [WeakReference, 383 refs,
0.0006608 secs]2016-08-24T10:33:04.735+0000: 8.462: [FinalReference,
4533 refs, 0.0020491 secs]2016-08-24T10:33:04.737+0000: 8.464:
[PhantomReference, 0 refs, 15 refs, 0.0011945
secs]2016-08-24T10:33:04.738+0000: 8.465: [JNI Weak Reference,
0.0000360 secs] 8.467: [G1Ergonomics (Mixed GCs) do not start mixed
GCs, reason: concurrent cycle is about to start]
2016-08-24T10:35:22.846+0000: 146.574: [SoftReference, 0 refs,
0.0011450 secs]2016-08-24T10:35:22.847+0000: 146.575: [WeakReference,
440 refs, 0.0006071 secs]2016-08-24T10:35:22.848+0000: 146.575:
[FinalReference, 7100 refs, 0.0018074
secs]2016-08-24T10:35:22.850+0000: 146.577: [PhantomReference, 0 refs,
76 refs, 0.0013148 secs]2016-08-24T10:35:22.851+0000: 146.579: [JNI
Weak Reference, 0.0000443 secs] 146.584: [G1Ergonomics (Mixed GCs) do
not start mixed GCs, reason: concurrent cycle is about to start]
2016-08-24T10:35:56.507+0000: 180.234: [SoftReference, 0 refs,
0.0010184 secs]2016-08-24T10:35:56.508+0000: 180.235: [WeakReference,
138 refs, 0.0006883 secs]2016-08-24T10:35:56.508+0000: 180.236:
[FinalReference, 3682 refs, 0.0023152
secs]2016-08-24T10:35:56.511+0000: 180.238: [PhantomReference, 0 refs,
45 refs, 0.0012558 secs]2016-08-24T10:35:56.512+0000: 180.239: [JNI
Weak Reference, 0.0000197 secs] 180.247: [G1Ergonomics (Mixed GCs) do
not start mixed GCs, reason: concurrent cycle is about to start]
The above entries should be okay.
2016-08-24T10:37:33.387+0000: 277.114: [SoftReference, 0 refs,
0.0010965 secs]2016-08-24T10:37:33.388+0000: 277.115: [WeakReference,
5 refs, 0.0006378 secs]2016-08-24T10:37:33.388+0000: 277.116:
[FinalReference, 3440 refs, 0.0028640
secs]2016-08-24T10:37:33.391+0000: 277.119: [PhantomReference, 0 refs,
0 refs, 0.0011392 secs]2016-08-24T10:37:33.392+0000: 277.120: [JNI
Weak Reference, 0.0000148 secs] 277.130: [G1Ergonomics (Mixed GCs) do
not start mixed GCs, reason: candidate old regions not available]
If these appear only during the startup, I won't worry about these too.
Do you see mixed GCs happening later during the run? If yes, then it's
just that the mixed GCs are not quite enough to keep pace with the
allocations/promotions into the old regions.
To increase the number of old regions included into the cset, you could
try increasing the value of /G1MixedGCLiveThresholdPercent.
/Thanks,
Poonam
Does that tell you anything?
Thanks,
Poonam
On 8/24/2016 3:18 PM, Jenny Zhang wrote:
More comments about the questions
Thanks
Jenny
On 8/24/2016 11:43 AM, Vitaly Davidovich wrote:
Right before the Full GC, ergonomics report a failure to expand
the heap due to an allocation request of 32 bytes. Is this
implying that a mutator tried to allocate 32 bytes but couldn't?
How do I reconcile that with Eden+Survivor occupancy reported
right above that?
Yes, it means the mutator tries to allocate 32byte but can not
get it. Heap won't expand as it already reaches max heap.
Do you see any humongous objects allocatoin?
Young gen is sized to 30GB, total heap is 96GB. Allocation rate
of the application is roughly 1GB/s. Am I correct in assuming
that allocation is outpacing concurrent marking, based on the
above? What tunable(s) would you advise to tweak to get G1 to
keep up with the allocation rate? I'm ok taking some throughput
hit to mitigate 90s+ pauses.
The entire log might give a better picture. Especially if the
marking cycle is triggered, how well the mixed gc cleans up the
heap.
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