Sustained high CPU on java server while doing nothing.

{{
PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND
66419 minecraft 44 52 0 3906M 2044M uwait 0 18.5H 100.05% java
}}

At this time, no one is using this server at all.
Restarting has approximately the same performance after the "preparing spaw area" peak.