Continuous CMS Collections Followed By Concurrent Mode Failure

Srinivas Ramakrishna ysr1729 at gmail.com
Tue Jul 8 00:37:45 UTC 2014


Haven't looked at yr log, but from yr description I suspect you need to
enable class unloading. That's one thing STW GC does by default that CMS
doesn't (at least until 7uXX) do by default.

-XX:+CMSClassUnoadingEnabled

-- ramki


On Mon, Jul 7, 2014 at 10:39 AM, Elliot Barlas <Elliot.Barlas at citrix.com>
wrote:

>  Hi all, I have a question about CMS collections and I'm hoping you can
> help.
>
>  The GC log for my Java application indicates continuous CMS GC followed
> by a concurrent mode failure stop-the-world collection that reclaims nearly
> the entire heap.
>
>  Why are the CMS collections failing to clear the old generation? Why is
> a concurrent mode failure stop-the-world collection required?
>
>  CMS collections like the one below occurred continuously for several
> days before a concurrent mode failure finally forced a stop-the-world
> collection that cleared space. Notice how the CMS collections recover
> almost no space, while the collection following the promotion failure
> reduces the old generation from 1.92 GB to 50.7 MB.
>
>  Is it due to objects kept alive by dead, uncollected objects in the
> permanent generation, which are only discarded during a STW collection?
> Should I consider using ‑XX:+CMSClassUnloadingEnabled to address this?
>
>
>  ----- Complete CMS collection in GC log -----
>
>  2014-06-10T22:54:45.999-0700: 4999434.771: [GC [1 CMS-initial-mark:
> 1920327K(1926784K)] 2050302K(2080128K), 0.3369430 secs] [Times: user=0.34
> sys=0.00, real=0.33 secs]
> 2014-06-10T22:54:46.338-0700: 4999435.111: [CMS-concurrent-mark-start]
> 2014-06-10T22:54:50.543-0700: 4999439.315: [CMS-concurrent-mark:
> 4.204/4.204 secs] [Times: user=4.21 sys=0.08, real=4.20 secs]
> 2014-06-10T22:54:50.543-0700: 4999439.315: [CMS-concurrent-preclean-start]
> 2014-06-10T22:54:50.573-0700: 4999439.345: [CMS-concurrent-preclean:
> 0.023/0.030 secs] [Times: user=0.02 sys=0.00, real=0.04 secs]
> 2014-06-10T22:54:50.573-0700: 4999439.346:
> [CMS-concurrent-abortable-preclean-start]
> 2014-06-10T22:54:54.599-0700: 4999443.371:
> [GC2014-06-10T22:54:54.599-0700: 4999443.372:    [ParNew
> Desired survivor size 8716288 bytes, new threshold 6 (max 6)
> - age   1:    1410440 bytes,    1410440 total
> - age   2:     181888 bytes,    1592328 total
> - age   3:     117864 bytes,    1710192 total
> - age   4:     136792 bytes,    1846984 total
> - age   5:     161296 bytes,    2008280 total
> - age   6:    2488416 bytes,    4496696 total
> : 141989K->5449K(153344K), 0.1317090 secs] 2062317K->1925911K(2080128K),
> 0.1321970 secs]    [Times: user=0.23 sys=0.01, real=0.14 secs]
>  CMS: abort preclean due to time 2014-06-10T22:54:55.606-0700:
> 4999444.378: [CMS-concurrent-abortable-preclean: 2.600/5.033 secs] [Times:
> user=2.88 sys=0.08, real=5.03 secs]
> 2014-06-10T22:54:55.611-0700: 4999444.384: [GC[YG occupancy: 10356 K
> (153344 K)]2014-06-10T22:54:55.612-0700: 4999444.384: [Rescan (parallel) ,
> 0.1665620 secs]2014-06-10T22:54:55.778-0700: 4
> 999444.550: [weak refs processing, 0.0000440
> secs]2014-06-10T22:54:55.778-0700: 4999444.551: [scrub string table,
> 0.0010220 secs] [1 CMS-remark: 1920462K(1926784K)] 1930818K(2080128K),
> 0.1678710 secs] [Times: user=0.28 sys=0.00, real=0.17 secs]
> 2014-06-10T22:54:55.780-0700: 4999444.552: [CMS-concurrent-sweep-start]
> 2014-06-10T22:54:57.554-0700: 4999446.326: [CMS-concurrent-sweep:
> 1.775/1.775 secs]    [Times: user=1.82 sys=0.01, real=1.78 secs]
> 2014-06-10T22:54:57.554-0700: 4999446.327: [CMS-concurrent-reset-start]
> 2014-06-10T22:54:57.564-0700: 4999446.336: [CMS-concurrent-reset:
> 0.009/0.009 secs] [Times: user=0.01 sys=0.01, real=0.01 secs]
>
>
>  ----- Concurrent mode failure GC log ------
>
>  2014-06-10T22:56:18.793-0700: 4999527.565: [GC [1 CMS-initial-mark:
> 1920286K(1926784K)] 2051254K(2080128K), 0.3388330 secs] [Times: user=0.33
> sys=0.00, real=0.33 secs]
> 2014-06-10T22:56:19.132-0700: 4999527.904: [CMS-concurrent-mark-start]
> 2014-06-10T22:56:23.112-0700: 4999531.884: [CMS-concurrent-mark:
> 3.976/3.980 secs] [Times: user=4.07 sys=0.04, real=3.99 secs]
> 2014-06-10T22:56:23.112-0700: 4999531.885: [CMS-concurrent-preclean-start]
> 2014-06-10T22:56:23.141-0700: 4999531.914: [CMS-concurrent-preclean:
> 0.022/0.029 secs] [Times: user=0.01 sys=0.01, real=0.03 secs]
> 2014-06-10T22:56:23.141-0700: 4999531.914:
> [CMS-concurrent-abortable-preclean-start]
> 2014-06-10T22:56:26.242-0700: 4999535.014:
> [GC2014-06-10T22:56:26.242-0700: 4999535.014:
> [ParNew2014-06-10T22:56:26.256-0700: 4999535.028:
> [CMS-concurrent-abortable-preclean: 1.948/3.114 secs] [Times: user=1.93
> sys=0.12, real=3.11 secs]
>  (promotion failed)
> Desired survivor size 8716288 bytes, new threshold 6 (max 6)
> - age   1:    1036320 bytes,    1036320 total
> - age   2:     825248 bytes,    1861568 total
> - age   3:     119024 bytes,    1980592 total
> - age   4:     113784 bytes,    2094376 total
> - age   5:     129024 bytes,    2223400 total
> - age   6:     154976 bytes,    2378376 total
> : 141769K->140729K(153344K), 0.3807730 secs]2014-06-10T22:56:26.623-0700:
> 4999535.395: [CMS
>  (concurrent mode failure): 1920816K->50773K(1926784K), 28.3938140 secs]
> 2062055K->50773K(2080128K), [CMS Perm : 48657K->41071K(262144K)],
> 28.7750370 secs] [Times: user=1.65 sys=0.03, real=28.78 secs]
>
>
>  ----- Background -----
>
>  $ /usr/java/jdk1.7.0_51/bin/java -version
>
> java version "1.7.0_51"
>
> Java(TM) SE Runtime Environment (build 1.7.0_51-b13)
>
> Java HotSpot(TM) 64-Bit Server VM (build 24.51-b03, mixed mode)
>
>
>  -Xms2048m
>
> -Xmx2048m
>
> -XX:PermSize=256m
>
> -XX:MaxPermSize=256m
>
> -XX:+UseConcMarkSweepGC
>
> -XX:+PrintClassHistogram
>
> -XX:+DisableExplicitGC
>
> -XX:+PrintGCDateStamps
>
> -XX:+PrintGCDetails
>
> -XX:+PrintTenuringDistribution
>
> -XX:+HeapDumpOnOutOfMemoryError
>
> -XX:HeapDumpPath=<logs dir>
>
> -Xloggc:<log path>
>
>  Thanks,
> Elliot
>
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