Interpreting Concurrent Mark Sweep GC-Log

Question

Hi.
I am trying to extract some metrics from the garbage collector log of the concurrent mark sweep garbage collector. I have found a nice walkthrough a this site:
[http://www.sun.com/bigadmin/content/submitted/cms_gc_logs.html |http://www.sun.com/bigadmin/content/submitted/cms_gc_logs.html ]
I'm using CMS in incremental mode and that's where I am having interpretation problems. The site above states that the incremental mode takes over the job of the "concurrent mark"-phase. If this is correct (is it?) that means that I have two different statistics that state how long the "concurrent mark"-phase took. First the incremental CMS statistics and second the ordinary CMS statistics.
The first incremental stats look like this:
2803.125: [GC 2803.125: [ParNew: 408832K->0K(409216K), 0.5371950 secs]
           611130K->206985K(1048192K) icms_dc=4 , 0.5373720 secs]
2824.209: [GC 2824.209: [ParNew: 408832K->0K(409216K), 0.6755540 secs]
           615806K->211897K(1048192K) icms_dc=4 , 0.6757740 secs] The second ordinary statistics look like this:
40.683: [CMS-concurrent-mark: 0.521/0.529 secs]I'm wondering wether the second (ordinary) statistics are still valid when using incremental mode.
Kind regards
Frank

Answer 1

40.683: [CMS-concurrent-mark: 0.521/0.529 secs]
Yes, these logs are still valid. icms_dc indicates the time in percentage that the concurrent work took between two young GCs.
e.g. for the following logs:
-->1.289: [GC 1.289: [DefNew: 1984K->191K(1984K), 0.1952985 secs] 5695K->5714K(7648K) icms_dc=55 , 0.1956749 secs] [Times: user=0.19 sys=0.00, real=0.20 secs]
1.488: [CMS-concurrent-reset-start]
1.494: [CMS-concurrent-reset: 0.006/0.006 secs] [Times: user=0.00 sys=0.00, real=0.01 secs]
1.503: [GC [1 CMS-initial-mark: 5522K(9208K)] 6715K(11192K), 0.0191550 secs] [Times: user=0.02 sys=0.00, real=0.02 secs]
1.522: [CMS-concurrent-mark-start]
-->1.531: [GC 1.531: [DefNew: 1710K->192K(1984K), 0.1260654 secs] 7232K->7220K(11192K) icms_dc=70 , 0.1265609 secs] [Times: user=0.10 sys=0.02, real=0.13 secs]
2.051: [CMS-concurrent-mark: 0.401/0.528 secs] [Times: user=0.50 sys=0.03, real=0.53 secs]
Concurrent work took around 70% of the time between the two young GCs at 1.531 and 1.289. Here, some part of CMS-concurrent-mark work was done before the second young GC and rest after that. And overall CMS-concurrent-mark phase ran for 0.401s out of total (2.051-1.522=) 0.529s.