unicorn_stderr.log; worker timeout; killing

Hello,

for two days now I have severe problems with Gitlab, because it becomes very slow and unresponsive.

Looking at the Gitlab Log afterwards I always find logs that look similar to the following. The following log extract is from 5 minutes ago:

==> /var/log/gitlab/unicorn/unicorn_stderr.log <== I, [2016-03-29T12:28:19.050743 #24382] INFO -- : worker=4 spawned pid=24382 I, [2016-03-29T12:28:19.051384 #24382] INFO -- : worker=4 ready E, [2016-03-29T13:15:25.480071 #1309] ERROR -- : worker=4 PID:24382 timeout (61s > 60s), killing E, [2016-03-29T13:15:26.744892 #1309] ERROR -- : reaped #<Process::Status: pid 24382 SIGKILL (signal 9)> worker=4 I, [2016-03-29T13:15:27.638015 #30867] INFO -- : worker=4 spawned pid=30867 I, [2016-03-29T13:15:27.843049 #30867] INFO -- : worker=4 ready E, [2016-03-29T13:18:15.443496 #1309] ERROR -- : worker=4 PID:30867 timeout (61s > 60s), killing E, [2016-03-29T13:18:15.652487 #1309] ERROR -- : reaped #<Process::Status: pid 30867 SIGKILL (signal 9)> worker=4 I, [2016-03-29T13:18:15.677140 #31308] INFO -- : worker=4 spawned pid=31308 I, [2016-03-29T13:18:15.678138 #31308] INFO -- : worker=4 ready

I am currently running the following software:

Ubuntu 14.04.4 with Kernel 3.13.0-83-generic
Gitlab 8.5.6

What do you think causes those problems? I am just curious. I think that I am switching the whole Gitlab to Debian tomorrow, because last time I did not have good experiences with Ubuntu.

Kind regards,
Stefan