JVM CMS Garbage Collecting Issues
- by jlintz
I'm seeing the following symptoms on an application's GC log file with the Concurrent Mark-Sweep collector:
4031.248: [CMS-concurrent-preclean-start]
4031.250: [CMS-concurrent-preclean: 0.002/0.002 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
4031.250: [CMS-concurrent-abortable-preclean-start]
CMS: abort preclean due to time 4036.346: [CMS-concurrent-abortable-preclean: 0.159/5.096 secs] [Times: user=0.00 sys=0.01, real=5.09 secs]
4036.346: [GC[YG occupancy: 55964 K (118016 K)]4036.347: [Rescan (parallel) , 0.0641200 secs]4036.411: [weak refs processing, 0.0001300 secs]4036.411: [class unloading, 0.0041590 secs]4036.415: [scrub symbol & string tables, 0.0053220 secs] [1 CMS-remark: 16015K(393216K)] 71979K(511232K), 0.0746640 secs] [Times: user=0.08 sys=0.00, real=0.08 secs]
The preclean process keeps aborting continously. I've tried adjusting CMSMaxAbortablePrecleanTime to 15 seconds, from the default of 5, but that has not helped. The current JVM options are as follows...
Djava.awt.headless=true
-Xms512m
-Xmx512m
-Xmn128m
-XX:MaxPermSize=128m
-XX:+HeapDumpOnOutOfMemoryError
-XX:+UseParNewGC
-XX:+UseConcMarkSweepGC
-XX:BiasedLockingStartupDelay=0
-XX:+DoEscapeAnalysis
-XX:+UseBiasedLocking
-XX:+EliminateLocks
-XX:+CMSParallelRemarkEnabled
-verbose:gc
-XX:+PrintGCTimeStamps
-XX:+PrintGCDetails
-XX:+PrintHeapAtGC
-Xloggc:gc.log
-XX:+CMSClassUnloadingEnabled
-XX:+CMSPermGenPrecleaningEnabled
-XX:CMSInitiatingOccupancyFraction=50
-XX:ReservedCodeCacheSize=64m
-Dnetworkaddress.cache.ttl=30
-Xss128k
It appears the concurrent-abortable-preclean never gets a chance to run. I read through http://blogs.sun.com/jonthecollector/entry/did_you_know which had a suggestion of enabling CMSScavengeBeforeRemark, but the side effects of pausing did not seem ideal. Could anyone offer up any suggestions?
Also I was wondering if anyone had a good reference for grokking the CMS GC logs, in particular this line:
[1 CMS-remark: 16015K(393216K)] 71979K(511232K), 0.0746640 secs]
Not clear on what memory regions those numbers are referring to.
