G1 - Mixed and Full GC's
Gopal, Prasanna CWK
prasanna.gopal at blackrock.com
Thu Dec 15 12:29:25 UTC 2016
Hi Wolfgang
Thanks for your reply. Yes I agree we have high CPU overhead. We have the following settings for CPU-Cores / GC Threads.
virtualProcessorCount=48
ParallelGCThreads=8
> AFAIR humongous regions are only collected during mixed/full GC in your version.
This is my understanding as well, but I am not sure why these objects were not collected during Mixed GC cycles. The Mixed cycle is seeing only 29 MB as claimable, but the Full GC was able to claim 4041.8 MB within 100 ms
45349.970: [G1Ergonomics (Mixed GCs) do not start mixed GCs, reason: reclaimable percentage not over threshold, candidate old regions: 46 regions, reclaimable: 31277496 bytes (0.42 %), threshold: 10.00 %]
Regards
Prasanna
-----Original Message-----
From: hotspot-gc-use [mailto:hotspot-gc-use-bounces at openjdk.java.net] On Behalf Of Wolfgang Pedot
Sent: 15 December 2016 12:10
To: hotspot-gc-use at openjdk.java.net
Subject: Re: G1 - Mixed and Full GC's
Hi,
not sure about my "expert"-ness but something caught my eye:
you do have a pretty high GC overhead there (recent GC overhead: 30.14 %), it is possible that G1 can simply not keep up with your allocations and that leads to a full GC. How many CPU-cores does your machine have and how many GC threads are used?
Can you determine the size of your humongous objects? Getting rid of those by increasing the region-size could help, AFAIR humongous regions are only collected during mixed/full GC in your version.
regards
Wolfgang Pedot
Am 15.12.2016 um 10:44 schrieb Gopal, Prasanna CWK:
>
> Hi Experts
>
> We have one of our application running G1 with following
> configuration
>
> -Xmx7G
>
> -Xms7G
>
> -XX:+UseG1GC
>
> -XX:+UnlockExperimentalVMOptions
>
> -XX:InitiatingHeapOccupancyPercent=60
>
> -XX:G1ReservePercent=20
>
> -XX:G1MixedGCLiveThresholdPercent=85
>
> -XX:MaxGCPauseMillis=500
>
> -XX:+ParallelRefProcEnabled
>
> -XX:+PrintAdaptiveSizePolicy
>
> -XX:+PrintHeapAtGC
>
> -XX:+PrintReferenceGC
>
> -XX:+PrintGCDateStamps
>
> -XX:+PrintTenuringDistribution
>
> -XX:+PrintGCApplicationConcurrentTime
>
> -XX:+PrintGCApplicationStoppedTime
>
> -Duser.timezone=America/Los_Angeles
>
> -d64 -Dserver
>
> JDK : jdk_7u40_x64 ( Yes we need to move to latest JDK)
>
> We are seeing the following behaviour
>
> End of a concurrent cycle
>
> 2016-12-14T12:59:01.307-0500: 45342.193: Total time for which
> application threads were stopped: 0.0189970 seconds
>
> 2016-12-14T12:59:01.307-0500: 45342.193: Application time: 0.0001190
> seconds
>
> 2016-12-14T12:59:01.308-0500: 45342.193: *[GC cleanup
> 5093M->3488M(7168M), 0.0075650 secs] *
>
> [Times: user=0.06 sys=0.00, real=0.01 secs]
>
> 2016-12-14T12:59:01.315-0500: 45342.201: Total time for which
> application threads were stopped: 0.0081250 seconds
>
> 2016-12-14T12:59:01.315-0500: 45342.201: [GC concurrent-cleanup-start]
>
> 2016-12-14T12:59:01.318-0500: 45342.203: [GC concurrent-cleanup-end,
> 0.0022490 secs]
>
> After 8 Seconds, Minor GC kicks in and decides not to do any Mixed
> GC's
>
> 2016-12-14T12:59:09.083-0500: 45349.969: [PhantomReference, 0 refs,
> 0.0001880 secs]2016-12-14T12:59:09.083-0500: 45349.969: [JNI Weak
> Reference, 0.0000050 secs] 45349.970: [G1Ergonomics (Heap Sizing)
> attempt heap expansion, reason: recent GC overhead higher than
> threshold after GC, recent GC overhead: 30.14 %, threshold: 10.00 %,
> uncommitted: 0 bytes, calculated expansion amount: 0 bytes (20.00 %)]
>
> *45349.970: [G1Ergonomics (Concurrent Cycles) do not request
> concurrent cycle initiation, reason: still doing mixed collections,
> occupancy: 6926893056 bytes, allocation request: 0 bytes, threshold:
> 4509715620 bytes (60.00 %), source: end of GC]*
>
> *45349.970: [G1Ergonomics (Mixed GCs) do not start mixed GCs, reason:
> reclaimable percentage not over threshold, candidate old regions: 46
> regions, reclaimable: 31277496 bytes (0.42 %), threshold: 10.00 %]*
>
> , 0.0765450 secs]
>
> [Parallel Time: 74.1 ms, GC Workers: 8]
>
> [GC Worker Start (ms): Min: 45349894.0, Avg: 45349894.1, Max:
> 45349894.2, Diff: 0.3]
>
> [Ext Root Scanning (ms): Min: 4.3, Avg: 5.1, Max: 6.4, Diff:
> 2.1, Sum: 41.2]
>
> [Update RS (ms): Min: 64.6, Avg: 66.2, Max: 67.1, Diff: 2.5,
> Sum: 529.2]
>
> [Processed Buffers: Min: 324, Avg: 363.8, Max: 524, Diff:
> 200, Sum: 2910]
>
> [Scan RS (ms): Min: 0.0, Avg: 0.5, Max: 0.6, Diff: 0.6, Sum:
> 3.7]
>
> [Object Copy (ms): Min: 1.6, Avg: 2.0, Max: 2.3, Diff: 0.7, Sum:
> 15.9]
>
> [Termination (ms): Min: 0.0, Avg: 0.0, Max: 0.0, Diff: 0.0, Sum:
> 0.0]
>
> [GC Worker Other (ms): Min: 0.0, Avg: 0.0, Max: 0.1, Diff: 0.0,
> Sum: 0.4]
>
> [GC Worker Total (ms): Min: 73.7, Avg: 73.8, Max: 73.9, Diff:
> 0.2, Sum: 590.3]
>
> [GC Worker End (ms): Min: 45349967.8, Avg: 45349967.9, Max:
> 45349967.9, Diff: 0.0]
>
> [Code Root Fixup: 0.0 ms]
>
> [Clear CT: 0.1 ms]
>
> [Other: 2.3 ms]
>
> [Choose CSet: 0.0 ms]
>
> [Ref Proc: 1.2 ms]
>
> [Ref Enq: 0.2 ms]
>
> [Free CSet: 0.6 ms]
>
> [Eden: 310.0M(1382.0M)->0.0B(352.0M) Survivors: 4096.0K->6144.0K
> Heap: 6603.4M(7168.0M)->6297.9M(7168.0M)]
>
> Heap after GC invocations=4395 (full 207):
>
> garbage-first heap total 7340032K, used 6449092K
> [0x000000063ae00000, 0x00000007fae00000, 0x00000007fae00000)
>
> region size 2048K, 3 young (6144K), 3 survivors (6144K)
>
> compacting perm gen total 77824K, used 77354K [0x00000007fae00000,
> 0x00000007ffa00000, 0x0000000800000000)
>
> the space 77824K, 99% used [0x00000007fae00000,
> 0x00000007ff98a840, 0x00000007ff98aa00, 0x00000007ffa00000)
>
> No shared spaces configured.
>
> }
>
> [Times: user=0.60 sys=0.00, real=0.08 secs]
>
> Immediately after this another concurrent cycle kicks in
>
> 45349.974: [G1Ergonomics (Concurrent Cycles) request concurrent cycle
> initiation, reason: occupancy higher than threshold, occupancy:
> 6943670272 bytes, allocation request: 15728656 bytes, threshold:
> 4509715620 bytes (60.00 %), source: concurrent humongous allocation]
>
> 2016-12-14T12:59:09.088-0500: 45349.974: Application time: 0.0004930
> seconds
>
> 45349.974: [G1Ergonomics (Concurrent Cycles) request concurrent cycle
> initiation, reason: requested by GC cause, GC cause: G1 Humongous
> Allocation]
>
> Before the concurrent cycle can complete, Full GC kicks in
>
> 2016-12-14T12:59:09.195-0500: 45350.081: [*Full
> GC2016-12-14T12:59:11.445-0500: 45352.331*: [SoftReference, 765 refs,
> 0.0001920 secs]2016-12-14T12:59:11.445-0500: 45352.331:
> [WeakReference, 2417 refs, 0.0004400
> secs]2016-12-14T12:59:11.446-0500: 45352.331: [FinalReference, 898
> refs, 0.0001680 secs]2016-12-14T12:59:11.446-0500: 45352.332:
> [PhantomReference, 10 refs, 0.0000060
> secs]2016-12-14T12:59:11.446-0500: 45352.332: [JNI Weak Reference,
> 0.0000190 secs] 6557M->2515M(7168M), 6.1312980 secs]
>
> [Eden: 2048.0K(348.0M)->0.0B(3070.0M) Survivors: 10.0M->0.0B Heap/:
> 6557.1M(7168.0M)->2515.3M(7168.0M)]/
>
> It will be helpful for us to understand,
>
> 1)Why If Full GC can clean up nearly 4 GB (:
> 6557.1M(7168.0M)->2515.3M(7168.0M)]) , why didn't the mixed GC kicked
> in earlier ?. Does this mean all our old regions are tightly packed
> (greater than G1MixedGCLiveThresholdPercent=85 ) ?
>
> 2)We also see , high amount of Humongous object allocation. Could it
> be the case that Only Full GC's can remove the Humongous objects ?
>
> 3)Is there any other tuning parameters we can use to mitigate this
> scenario ?
>
> Please do let me know, if you need any more information. Thanks in
> advance for your help.
>
> Regards
>
> Prasanna
>
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