[Koha] Slow Koha OPAC login process

[Michael Kuhn]

Hi

We're running a new host with Debian GNU/Linux 8 and Koha 16.11.04.

Usually the Koha OPAC login process is quick as expected. But sometimes 
when trying to login it takes 10 to 40 seconds until the login process 
finally comes to an end. At such occasions the following process can be 
seen with "top", taking 99% of the CPU resources:

phsh-ko+ 59422 56031 11 16:30 ?        00:00:35 
/usr/share/koha/opac/cgi-bin/opac/opac-user.pl

This happens more often when trying to login from the internal network, 
and less often when trying to login from the external network (i. e. the 
internet).

Has anyone experienced this problem before and can maybe give us a hint 
how to tame "opac-user.pl"?

Best wishes and Happy Easter: Michael