This page describes a singular cause for Out Of Memory Heap Space Errors. Refer to JIRA Crashes Due to OutOfMemoryError Java heap space for a general discussion.
JIRA crashes or behaves unpredictably. Logs contain errors like:
Occasionally people write their own services, which can cause memory problems if (as is often the case) they iterate over large numbers of issues.
The CVS service is an example of one service that can cause memory problems, if used with a huge CVS repository (in this case, simply increase the allocated memory).
A symptom of a CVS (or general services-related) problem is that JIRA will run out of memory just minutes after startup.