Increased activity of mirroring leading to higher GitLab.com load

As of 14:00 UTC today we're seeing an increase in mirroring activity:

Screenshot_from_2017-02-09_17-30-11

A similar pattern is shown for the other mirroring queues/jobs. The pattern also repeats itself every hour, which is less than ideal. As a result the project_mirror queue is currently throttled at 80% capacity to ensure other jobs are not impacted too much.

@brodock @tiagonbotelho since both of you are involved with mirroring, could you try to look into this to see what change in 8.17 (which we deployed today) might be causing this?