Blocking queries in ci_commits: SELECT FOR UPDATE
At times we see Sidekiq queues growing large, we have also seen a lot of SELECT FOR UPDATE
queries on the ci_commits table:
https://gitlab.slack.com/files/stanhu/F2S398BNF/20161020-query.log
This may relate to the source of slowness in #584 (moved), but it's not for certain.
/cc: @ayufan, @pcarranza