Speed up `all_commit_shas` for new merge requests

For merge requests created after 9.4, we have a `merge_request_diff_commits` table we can get all the SHAs from very quickly. We just need to exclude these when we load from the legacy format, by ignoring diffs with no serialised commits. Once these have been migrated in the background, every MR will see this improvement.

Speed up `all_commit_shas` for new merge requests
4c0864fd · Sean McGivern · d40445e4 · 4c0864fd · 4c0864fd · 4c0864fd
Commit 4c0864fd authored Jul 07, 2017 by Sean McGivern
3 changed files
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -849,7 +849,10 @@ class MergeRequest < ActiveRecord::Base
  #
  def all_commit_shas
    if persisted?
-      merge_request_diffs.preload(:merge_request_diff_commits).flat_map(&:commit_shas).uniq
+      column_shas = MergeRequestDiffCommit.where(merge_request_diff: merge_request_diffs).pluck('DISTINCT(sha)')
+      serialised_shas = merge_request_diffs.where.not(st_commits: nil).flat_map(&:commit_shas)
+
+      (column_shas + serialised_shas).uniq
    elsif compare_commits
      compare_commits.to_a.reverse.map(&:id)
    else

--- a/changelogs/unreleased/speed-up-merge-request-all-commits-shas.yml
+++ b/changelogs/unreleased/speed-up-merge-request-all-commits-shas.yml
+---
+title: Make loading new merge requests (those created after the 9.4 upgrade) faster
+merge_request:
+author:
--- a/spec/models/merge_request_spec.rb
+++ b/spec/models/merge_request_spec.rb
@@ -803,7 +803,7 @@ describe MergeRequest, models: true do
      shared_examples 'returning all SHA' do
        it 'returns all SHA from all merge_request_diffs' do
          expect(subject.merge_request_diffs.size).to eq(2)
-          expect(subject.all_commit_shas).to eq(all_commit_shas)
+          expect(subject.all_commit_shas).to match_array(all_commit_shas)
        end
      end