Merge branch 'performance-improvements' into 'master'

Performance improvements

Push 1k commits cause 1k sql queries to collect commit author. But this variable was used only in 20 commits (from 1000).
So we did 980 sql queries without using it. This MR fixes it.

See merge request !1250

app/services/git_push_service.rb

@@ -83,9 +83,14 @@ class GitPushService
       # closing regex. Exclude any mentioned Issues from cross-referencing even if the commits are being pushed to
       # a different branch.
       issues_to_close = commit.closes_issues(project)
-      author = commit_user(commit)
 
-      if !issues_to_close.empty? && is_default_branch
+      # Load commit author only if needed.
+      # For push with 1k commits it prevents 900+ requests in database
+      author = nil
+
+      if issues_to_close.present? && is_default_branch
+        author ||= commit_user(commit)
+
         issues_to_close.each do |issue|
           Issues::CloseService.new(project, author, {}).execute(issue, commit)
         end
@@ -96,8 +101,13 @@ class GitPushService
       # being pushed to a different branch).
       refs = commit.references(project) - issues_to_close
       refs.reject! { |r| commit.has_mentioned?(r) }
-      refs.each do |r|
-        Note.create_cross_reference_note(r, commit, author, project)
+
+      if refs.present?
+        author ||= commit_user(commit)
+
+        refs.each do |r|
+          Note.create_cross_reference_note(r, commit, author, project)
+        end
       end
     end
   end