I recently ran into a server running Best Practical Request Tracker (RT) version 4.0.8 that was having major performance issues displaying certain pages and causing the system to run out of resources.
What was happening was that when a user would click to view a ticket or navigate around a tickets information, it would take a few minutes for the page to load; on the server the Apache processes (httpd) would be spiked at 100% CPU usage.
Here is the output from top for the httpd process while this was occurring.
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 6593 apache 25 0 2999m 2.5g 4924 R 100.0 16.0 4:31.66 httpd