1 files changed, 29 insertions, 3 deletions

diff --git a/app/finders/merge_requests/oldest_per_commit_finder.rb b/app/finders/merge_requests/oldest_per_commit_finder.rb
index f50db43d7d2..5360f301036 100644
--- a/app/finders/merge_requests/oldest_per_commit_finder.rb
+++ b/app/finders/merge_requests/oldest_per_commit_finder.rb
@@ -15,19 +15,45 @@ module MergeRequests
     # Returns a Hash that maps a commit ID to the oldest merge request that
     # introduced that commit.
     def execute(commits)
+      mapping = {}
+      shas = commits.map(&:id)
+
+      # To include merge requests by the commit SHA, we don't need to go through
+      # any diff rows.
+      #
+      # We can't squeeze all this into a single query, as the diff based data
+      # relies on a GROUP BY. On the other hand, retrieving MRs by their merge
+      # SHAs separately is much easier, and plenty fast.
+      @project
+        .merge_requests
+        .preload_target_project
+        .by_merge_commit_sha(shas)
+        .each do |mr|
+          # Merge SHAs can't be in the merge request itself. It _is_ possible a
+          # newer merge request includes the merge commit, but in that case we
+          # still want the oldest merge request.
+          mapping[mr.merge_commit_sha] = mr
+        end
+
+      remaining = shas - mapping.keys
+
+      return mapping if remaining.empty?
+
       id_rows = MergeRequestDiffCommit
-        .oldest_merge_request_id_per_commit(@project.id, commits.map(&:id))
+        .oldest_merge_request_id_per_commit(@project.id, remaining)
 
       mrs = MergeRequest
         .preload_target_project
         .id_in(id_rows.map { |r| r[:merge_request_id] })
         .index_by(&:id)
 
-      id_rows.each_with_object({}) do |row, hash|
+      id_rows.each do |row|
         if (mr = mrs[row[:merge_request_id]])
-          hash[row[:sha]] = mr
+          mapping[row[:sha]] = mr
         end
       end
+
+      mapping
     end
   end
 end