Problem

Confluence becomes unresponsive for an extended period of time seemingly due to garbage collection.

Diagnosis

In the log files for garbage collection, lines similar to the following will be found where the 'real' time taken to complete a full GC is significantly longer then the 'user' and 'sys' time.

604483.041: [Full GC [PSYoungGen: 6423K->0K(330816K)] [ParOldGen: 696445K->351646K(699072K)] 702869K->351646K(1029888K) [PSPermGen: 215670K->213733K(262144K)], 1044.1092830 secs] [Times: user=5.99 sys=7.58, real=1044.05 secs]

Cause

This is likely caused by a process called memory ballooning in Virtual environments.  What is happening is that the information in physical memory in use by the virtual machine is written out to a hard drive so that the same physical memory can be used by another virtual machine.  The result for Confluence is a long time waiting for the system to become available while all of the stored information is read off of the hard drive and back into physical memory so that garbage collecting can be done for the JVM.

Resolution

Disable memory ballooning for the virtual machine hosting Confluence, following the steps described in this KB article: https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1002586