Various GC (G1GC, CMS): Meaning of CollectionTime attribute of MBeans

[Stefan Wachter]

Hi all,

I have a cluster with Tomcat instances running on the nodes. (The 
cluster nodes are 64-Bit Linux machines with 37 GB memory and 8 
processors. Two Tomcat instances run on each machine. Every Tomcat 
instance has 10 GB of heap available. The nodes have Java 1.6.0_24 
installed.)

I would like to compare differenct GC settings and reduce the 
stop-the-world times. Is this possible using the information available 
by JMX?

At the moment I have three different settings with the following MBeans 
being registered:

1. No garbage collection configuration -> "PS MarkSweep" and "PS Scavenge".

2. Option "-XX:+UseG1GC" -> "G1 Old Generation" and "G1 Young Generation".

3. Option "-XX:+UseConcMarkSweepGC" -> "ConcurrentMarkSweep" and "ParNew".

Each of the MBeans has a "CollectionTime" attribute. What is the meaning 
of the attribute for each of the MBeans? Does the attribute reflect 
"stop-the-world" times? Should the attribute values of the two MBeans 
used in each configuration be summed?

If using the information available via JMX is not enough in order to 
determine stop-the-world times, how could this be done?

Thanks you for your attention & best regards

Stefan