Logstash keeps hanging


We are having an issue where logstash just hangs. When we strace -f the PID it starts working again. We tried upping the memory, but that did not fix it. We also tried kill -3 (see output below) and jstack, but still can't find the cause. Has anyone else seen this?


Sending logstash logs to /var/log/logstash/logstash.log.
The error reported is:
pattern %{NGUSERNAME} not defined

What does your config look like? What version are you on?