Hi Adam, Its a technical term & it just came to my mind by looking at the log, so dont worry much about it. (Basically hashMaps are used in the code.)
I think as suggested by everyone, now what you could do is: Follow these steps (before restarting the servers or tomcat) whenever occur this again. So we can dig up into source of the problem.
I found a well written article on SO about it, so you can easily follow it: http://code.nomad-labs.com/2010/11/18/identifying-which-java-thread-is-consuming-most-cpu/
In short what you need to do is.
- run
top -H(on *nix terminal) - get PID of the thread with highest CPU
- get stack dump of java process:
jstack <Chosen PID>: it would be better to get multiple dumps in regular intervals. I have updated the instructions here: https://wiki.openmrs.org/display/docs/Troubleshooting+High+CPU+Utilization#Getting stack dump of Java process. - convert the chosen PID to HEX : 0x + http://www.binaryhexconverter.com/decimal-to-hex-converter
- in stack dumps look for thread with the matching HEX PID.
After that you can report us with your findings / File a ticket on OpenMRS jira. Otherwise its very difficult to exactly say what causing this problem. Other than OpenMRS system issues, it also could be your Ubuntu server configuration error/issues of other installed applications/Java-JRE issue/etc.
HTH, Harsha