Merge branch 'fix/use-fewer-queries-for-mr-notes' into 'master'
Reduce number of queries made for merge_requests/:id/diffs ## What does this MR do? It reduces the number of DB queries made while processing and rendering MR notes. ## Are there points in the code the reviewer needs to double check? N/A ## Why was this MR needed? For `https://staging.gitlab.com/gitlab-org/gitlab-ce/merge_requests/3142/diffs.json`, for each note we make number of DB queries, almost all of them are handled by the AR caching layer, but they seem to add up a few seconds. Testing on staging, calling `merge_requests/3142/diffs.json` was reduced to ~5.5 seconds from ~8 seconds. ## What are the relevant issue numbers? N/A ## Screenshots (if relevant) N/A ## Does this MR meet the acceptance criteria? - [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added - [ ] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~ - [ ] ~~API support added~~ - ~~Tests~~ - [ ] ~~Added for this feature/bug~~ - [ ] ~~All builds are passing~~ - [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides) - [x] Branch has no merge conflicts with `master` (if you do - rebase it please) - [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits) See merge request !5551
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