1

One of our java application is taking big pause while doing GC, it seems because of "ParNew (promotion failed)" it takes time.

Java version:

$ java -version
java version "1.6.0_21"
Java(TM) SE Runtime Environment (build 1.6.0_21-b06)
Java HotSpot(TM) 64-Bit Server VM (build 17.0-b16, mixed mode)

GC setting:

JAVA_OPTS="$JAVA_OPTS -XX:+PrintGCApplicationConcurrentTime -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintTenuringDistribution -Dsun.rmi.dgc.client.gcInterval=86400000 -Dsun.rmi.dgc.server.gcInterval=86400000 -verbose:gc -Xloggc:/path/to/gc/gc.log"
JAVA_OPTS="$JAVA_OPTS  -XX:NewSize=5g -XX:MaxNewSize=5g -Xms10g -Xmx10g -XX:PermSize=512m -XX:MaxPermSize=512m -XX:SurvivorRatio=30 -XX:TargetSurvivorRatio=90 -XX:MaxTenuringThreshold=15"
# Parallel setting
JAVA_OPTS="$JAVA_OPTS -XX:+UseParNewGC -XX:ParallelGCThreads=16"
# CMS setting
JAVA_OPTS="$JAVA_OPTS  -XX:+UseConcMarkSweepGC -XX:+CMSParallelRemarkEnabled -XX:+CMSCompactWhenClearAllSoftRefs -XX:CMSInitiatingOccupancyFraction=85 -XX:+CMSScavengeBeforeRemark -XX:+CMSConcurrentMTEnabled -XX:ParallelCMSThreads=2"

Here is gc.log output for few long pauses:

2015-06-04T10:02:28.988+0000: 129998.706: [GC[YG occupancy: 1904924 K (5079040 K)]2015-06-04T10:02:28.988+0000: 129998.706: [GC 129998.706: [ParNew (promotion
 failed)
Desired survivor size 150994944 bytes, new threshold 10 (max 15)
- age   1:   39557704 bytes,   39557704 total
- age   2:   23752968 bytes,   63310672 total
- age   3:   11024200 bytes,   74334872 total
- age   4:   10529816 bytes,   84864688 total
- age   5:    9602712 bytes,   94467400 total
- age   6:    9621976 bytes,  104089376 total
- age   7:   27355240 bytes,  131444616 total
- age   8:    6326944 bytes,  137771560 total
- age   9:    7153592 bytes,  144925152 total
- age  10:    6944200 bytes,  151869352 total
- age  11:    7226592 bytes,  159095944 total
- age  12:    6674048 bytes,  165769992 total
: 1904924K->1904924K(5079040K), 84.3892780 secs] 6687900K-     >7143259K(10321920K), 84.3894730 secs] [Times: user=241.33 sys=9.83,  real=84.39 secs]
130083.096: [Rescan (parallel) , 1.0518870 secs]130084.148: [weak refs     processing, 0.0056350 secs] [1 CMS-remark: 5238334K(5242880K)]   7143259K(10321920K), 85.
4473940 secs] [Times: user=249.44 sys=10.00, real=85.44 secs]
Total time for which application threads were stopped: 85.4485540 seconds

2015-06-09T01:36:38.354+0000: 531648.072: [GC[YG occupancy: 3444075 K (5079040 K)]2015-06-09T01:36:38.354+0000: 531648.072: [GC 531648.072: [ParNew (promotion
 failed)
Desired survivor size 150994944 bytes, new threshold 6 (max 15)
- age   1:  118719600 bytes,  118719600 total
- age   2:   20791640 bytes,  139511240 total
- age   3:    2411752 bytes,  141922992 total
- age   4:    3146888 bytes,  145069880 total
- age   5:    3595160 bytes,  148665040 total
- age   6:    3950560 bytes,  152615600 total
- age   7:    2455960 bytes,  155071560 total
- age   8:    2780536 bytes,  157852096 total
- age   9:    2346000 bytes,  160198096 total
- age  10:    2952600 bytes,  163150696 total
- age  11:    1078304 bytes,  164229000 total
- age  12:    1857992 bytes,  166086992 total
- age  13:    1093752 bytes,  167180744 total
: 3444075K->3444075K(5079040K), 53.3528910 secs] 7494225K->8679897K(10321920K), 53.3531460 secs] [Times: user=168.75 sys=10.21, real=53.36 secs]
531701.426: [Rescan (parallel) , 1.2041260 secs]531702.630: [weak refs processing, 0.0002920 secs] [1 CMS-remark: 5235821K(5242880K)] 8679897K(10321920K), 54.
5583950 secs] [Times: user=178.02 sys=10.43, real=54.57 secs]
Total time for which application threads were stopped: 54.5615990 seconds
2015-06-09T01:37:32.913+0000: 531702.631: [CMS-concurrent-sweep-start]


2015-06-10T12:58:53.687+0000: 658983.405: [GC 658983.405: [ParNew (promotion failed)
Desired survivor size 150994944 bytes, new threshold 11 (max 15)
- age   1:   62173384 bytes,   62173384 total
- age   2:    4913808 bytes,   67087192 total
- age   3:   10095568 bytes,   77182760 total
- age   4:   12476376 bytes,   89659136 total
- age   5:    8521376 bytes,   98180512 total
- age   6:     985064 bytes,   99165576 total
- age   7:    8824120 bytes,  107989696 total
- age   8:    9991888 bytes,  117981584 total
- age   9:   23527832 bytes,  141509416 total
- age  10:    5438928 bytes,  146948344 total
- age  11:    6171880 bytes,  153120224 total
- age  12:    6983376 bytes,  160103600 total
- age  13:    1196080 bytes,  161299680 total
- age  14:    5357040 bytes,  166656720 total
: 5079040K->5079040K(5079040K), 31.3569910 secs]659014.762: [CMS: 5239285K->5242879K(5242880K), 11.5386160 secs] 9441788K->5341454K(10321920K), [CMS Perm : 42
6919K->426638K(524288K)], 42.8959280 secs] [Times: user=120.92 sys=7.35, real=42.90 secs]
Total time for which application threads were stopped: 42.8996760 seconds
Application time: 0.0001030 seconds
2015-06-10T12:59:36.587+0000: 659026.305: [GC [1 CMS-initial-mark: 5242879K(5242880K)] 5343035K(10321920K), 0.0946190 secs] [Times: user=0.09 sys=0.00, real=0.09 secs]
Total time for which application threads were stopped: 0.0979600 seconds
2015-06-10T12:59:36.682+0000: 659026.400: [CMS-concurrent-mark-start]
Application time: 0.2920200 seconds

How can I troubleshoot this, it there something wrong in GC settings?

3

Updating to a newer version of Java 1.6 may help. Some of the patches related to GC behavior.

It appears the new size is extremely excessive. You have generally a few Mb surviving a new generation GC, and that seems to be destined for Old Generation. Try dropping the -XX:NewSize to somewhere between to 128m to 512m. It likely won't hurt to remove the -XX:MaxNewSize=5g setting.

These setting are likely causing an issue -XX:SurvivorRatio=30 -XX:TargetSurvivorRatio=90 -XX:MaxTenuringThreshold=15". Try just setting -XX:SurvivorRatio=32. These settings will cause the GC routines to continually try to resize the Survivor ratio. You are getting survivor ratios around 10 to 15. Monitor the survivor occupancy and adjust so that it is close to full.

You likely want a -XX:MaxTenuringThreshold setting of 4 or less. The more objects you have in new generation during the slower concurrent GC will be. You want new generation as close to empty as possible during the initial mark. From my tests all objects in the new generation are considered live during the concurrent mark process. As the time taken by the marking process is proportional to the number of live objects this can be a heavy penalty. With a lower setting you may be able to increase the survivor ratio.

The setting -XX:+PrintGCApplicationConcurrentTime -XX:+PrintGCApplicationStoppedTime tend to clutter the log and may not yield much useful information. I would remove them.

You may want to increase the number of threads used for Concurrent GC. Consider 25% of the CPU threads.

Consider dropping the -XX:CMSInitiatingOccupancyFraction to the range of 70 to 75. Because of the size of the memory allocation you may be OK with 85%. If memory gets too fragmented, you will get a long pause while memory is compacted.

Consider dropping overall memory specified in -Xms -Xmx to 5g or 6g. You may want to target having old generation GCs every 1 to 4 hours. If memory gets paged out between GC cycles, you may have wait for it to be paged in. This is can significantly increase GC times. You may need more old generation to support the lower initiating occupancy.

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