Server statistics: Slow Query

Steps to reproduce:
1. Go to Systems->Servers on a system with a lot of rows in mh_jobs (100'000+++)
2. Open inspect in your web browser to see how long the calls take

Actual Results:
Slow performance (6 seconds+ on our system for a single call)

Expected Results:
Fast performance

It is the following query that makes Systems->Servers so slow:

SELECT t0.id, t1.status, COUNT(t1.status), AVG(t1.queue_time), AVG(t1.run_time) FROM mh_service_registration t0, mh_job t1 WHERE (t0.id = t1.processor_service) GROUP BY t0.id, t0.active, t0.error_state_trigger, t0.job_producer, t0.online, t0.online_from, t0.path, t0.service_state, t0.service_type, t0.state_changed, t0.warning_state_trigger, t0.host_registration, t1.status

Note that this does not scale... on our system with 400'000+ entries in mh_jobs, the SQL-query alone takes more than 5 seconds.

Possible solution: Need to limit the number of mh_job rows to a reasonable number so that the query above has a reasonable runtime.