WIP: Improve participants performance

Open username-removed-7736 requested to merge hiroponz/gitlab-ce:new-participants into master

What does this MR do?

Improve participants performance

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?


Edited by username-removed-7736